Below is the procedure Rusty Marlin provided. He has continued to update and expand the information to help us all.I have slightly edited it for readability and format.
NOTE: Marlin Firearms warns that these old guns are not safe to shoot using modern ammunition.
– Marauder

See the Video

The following procedures are I take the 1898 series Marlin shotgun apart.There are numerous models that follow the basic building blocks of the original 1889 patents (yes, that date is correct).I have also included a plethora of detail on inspection and cleaning for the first time you take the gun apart.Most of these old girls are getting on toward the 100-year mark and there are lots of things to check that are not normally required during a standard cleaning.

Working at a steady pace, plan on taking a couple of evenings

Disclaimer

-I am not a certified gunsmith. I am an avid shooter that has taken the time and effort required to know how my guns work, all my guns. How to repair them and how to provide the preventive maintenance they require. I am very proud of the fact that I have never needed to leave a firearm with a gunsmith for a problem. To explain this, let me give you some background. I am a degreed Mechanical Engineer, a Manufacturing Engineer by trade, a former Tool Maker, a former machine tool assembler and a very patient tinkerer that is willing to admit ignorance and not afraid to ask questions of those with more knowledge and experience. My humble opinion is this: if we need to individually access our ability for this type of work. Am I capable of doing adequately and safely or should I find a qualified individual to do it for me. You don’t want to mess with something that could take your fool head off if you screw it up.

-If you don’t know the names of the basic parts of the gun, please don’t do this. Or to say it in another way - DON”T FRIGGIN’ TOUCH NOTHIN’! If that sounds pretty crude, Tough. If there is a box of parts in front of you and you can’t tell the difference between the extractor and the ejector, you have no business, whatsoever, taking your gun apart! Period. There is a pile of parts in these things that you may never have seen or heard of before; you should at least be able to pick out the parts that are common to, virtually all, modern firearms. I’m not worried about you knowing what the “secondary sear” is or where the “forward slide stop” is. These things I will explain in the text. But you ought to know what the “hammer” is and what the “shell carrier” does and where they can be found.

Generally you want to reassemble subassemblies before you go on to something else. The bolt assembly is a prime example. There are 14 parts in the bolt assembly, do you really want to try and figure out how they go back together a week after you get them apart?

Where I felt it warranted I also include the operating theory on how various assemblies work together.While you might not want all this information, I find it fascinating. You may need it some day when a less enlightened individual informs you that Marlin shotguns are “Widow makers” and should all be relegated to the den wall.Hopefully you will be able to educate this poor soul on the mechanical operating theory and genius of the action and even manage do so politely.

Before I tell you what you need to know about tearing apart your favorite Marlin 1898 shotgun there are some items that I want to get out of the way so we are all on the same page of music, so to speak.

-First and Foremost

Read this all the way through to make sure you really want to do this.

Safety Issue.

Make absolutely sure the gun is unloaded, both the chamber and magazine before proceeding with the disassembly.If this is a new purchase you will want to go through the following safety checks to give you an idea of any current problems.

Safety Checks

The Marlin shotguns have several safety devices inside to prevent the gun from firing out of battery. There are four checks that can be done without taking the gun apart that will tell you immediately if the gun has any chance of firing out of battery and throwing the bolt out the back of the receiver.(Notice I didn't mention the possibility of a cracked receiver or you if are planning on shooting magnum turkey loads.)

1) With an empty gun, hold the trigger back and gently slide the bolt forward with the pump arm until the bolt clears the top of the hammer.If the hammer follows along behind, STOP. It means the secondary sear spring could be broken and the gun could (BIG MAYBE) slam fire without the breech locked. If the hammer top is worn or it was excessively polished to help smooth the action, the secondary sear may not pick up its sear ledge on the hammer, which could cause the same problem. To determine if this is the case open the action up fully and then pull the hammer back more by hand. If you hear a click and the hammer stays back while the trigger is pulled, and the bolt slid forward, this is the root cause. To fix this you can weld up the top of the hammer and file it back to fit or you can take a file swipe or two across the sear nose on the secondary sear.Make sure the angle is kept at 90 degrees.There is a section in the text that deals specifically with the secondary sear’s function and how to get to it.

2) I'll assume the hammer stayed cocked. Open the receiver and apply pressure to the back of the firing pin with your thumb, it should not move much and come up solid before the firing pin tip protrudes from the breech face. If it protrudes from the breech face, STOP. This means the firing pin locking horn on the rotating breech lock is not functioning. (Read; worn off, broken, tampered with, etc.) Under high speed cycling the firing pin could be thrown forward under inertia and fire the shell in the chamber in a slam fire without the action being in full-locked battery. The best fix is to get a new locking lug. A reasonable fix is to have the horn welded up and refit. I don’t recommend this unless you are very good with a file and know exactly what you are doing.

3) Close the action slowly and deliberately with pressure applied to the rear of the firing pin with your thumb. As the rotating breech lock goes into battery the firing pin will become free to push through the face of the breech. THIS IS NORMAL. It means the breach lock is rotating properly. If the firing pin stays locked back there is a problem most likely with the cam groove that actuates the locking bolt. I have seen some that are highly worn. When the action was closed slowly it would not lock, when slammed closed it would lock. That is not good as eventually it would not lock at all, and possibly fire unlocked.

4) Last, but by no means least, with action closed Gently lower the hammer to rest on the firing pin or use your thumb to depress it, (if its loaded, always use your thumb). The action should NOT open with rearward pressure applied to the forearm.If it opens, STOP. The recoil lock isn’t engaging properly. To get the breech open you have to depress the safety latch and the firing pin simultaneously to open the bolt. The manual override for the recoil safety is up near the hammer on the older models or down near the trigger for newer models. THIS IS NORMAL. This test tells you if the locking lug is rotating completely into battery and that the recoil lock is working. It also may tell you if the lock is broken, or in need of adjustment. (It takes a trained ear to hear it lock in.)

If ANY of those tests failed the gun will need to be repaired, that simple.

If the gun passed all these tests, GREAT!!! - But with the older metals, some frames have failed even after passing the tests.

Remember to go through these checks before every match.

Recommended Requirements

-Get a set of high quality gunsmith screwdrivers before you disassemble anything. They will make your life much more pleasant because you are less likely to strip a screw and put a gouge across the finish of your firearm, or your hide. A decent set of punches will be needed for this job too.

-Work in a place that has good lighting with few shadows.Keep a small flashlight handy for those hidden areas that need a little extra light.

-Remove distractions from your work area; pets, kids, spouse, etc. Trust me there are few things more irritating than having your dog jump on you just as you take the lid off the Hoppes, or your loving spouse interrupting you in the middle of a critical step.

-Make sure your work surface is solid with plenty of area to set aside parts, tools and other materials. Mine is a 4’x 4’ drafting table set at 45 inches off the floor.I prefer to stand.

-In the following instructions I will be telling you how to hold the gun or receiver and in what attitude so that if you need to e-mail me to ask questions we are both doing the same thing in the same way.I take my pump Marlins apart, down to the screws, every three or four matches depending on how much they get used and if I get rained on or not.

The basic directions and labels: “up” is always toward the ceiling, and “down” is always toward the floor, regardless of the attitude of the receiver.

The top of the receiver is the surface you would be looking over when the gun in its normal firing attitude.
The bottom of the receiver is where the shell carrier is.
The left side of the receiver is the side to the left when in the normal firing attitude and the obviously the right side is opposite the left.
The front is where the barrel is attached, and the back is where the stock is attached. These labels are also regardless of what attitude the receiver is in.

- When I say to polish a surface, I don’t mean take the surface down to a smooth shiny mirror. In fact you are better off not removing any material at all. Polishing in this text generally means to clean the 90 or so years of accumulated oil varnish, gunk, and powder residue off the sliding surfaces and bring the under laying steel to a clean luster. Steel or bronze wool works fantastic for much of this.If you feel the need to remove material, use as fine a hard Arkansas stone that you can find. In areas where you might need something more aggressive I have pointed this out.

-Relax, this isn’t brain surgery, it’s a learning experience.Besides my e-mail address is at the end if you get totally confused.

What Model Do You Have?

Generally this is an easy step as Marlin put the model types on the rear tang of the receiver. Some don’t have this however. The original 1898 doesn’t and neither does the “Trap Gun”. From what I have been told by others, the contract guns built by Marlin for other companies to sell didn’t either.

The Trap Gun (synonymous with the Model 24) was built latter than the 1898 and can be differentiated from its parent model by the method of take down.1898’s use the Push Button method and the 24’s use a Pinch Block (a latch) at the muzzle end of the magazine tube.The Pinch Block was a design improvement that was used on the following Models, 19G, “the Trap Gun”, 24, 30, 42 and 42A and the 49. It may have been used on others too, but I haven’t seen all the models to be positive.

Assemblies

Removing The Barrel And Magazine Assembly

For full teardown, and to facilitate cleaning and inspection - take the barrel and magazine assembly off the receiver. (If the barrel hasn’t been cut, it is rather long and unwieldy at the bench; it is a fantastic light bulb smasher, shelf sweeper, ceiling scraper and a general a nuisance in a cramped space.) If you have a Model 17 or 26 you are stuck with the inconvenience of the barreled action. These are solid frame guns and hence you cannot remove the barrel from the action.If you have a 17 or 26 please skip ahead to the paragraph titled, Removing the Stock.

All the other models are “Take Down” shotguns that allow the barrel to be removed from the action. Of these types there are two different methods used to retain the magazine tube to the barrel lug. The first and older method found on the 1898, 19, and several other models, uses a pushbutton lock, out at the muzzle end of the magazine tube.The second method has a pinch block at the muzzle end of the magazine tube.

Push Button Version- Start with the action closed and the hammer down.

Push and hold the button in while turning the magazine tube to the left.
When it stops, pull it out of the receiver toward the muzzle and it will snap over the same push button - but in a different hole in the tube.
Now pull the pump arm forward slightly and the fore end slide stop will align with a notch in the top of the pump arm. The slide stop is tight to the front of the receiver and is L shaped; it’s in a notch cut into the side of the barrel.
Flick the stop into the notch on the pump arm with your finger and pull the pump arm all the way forwards so the end that is normally inside the receiver is clear. The slide stop will travel with the pump arm.

Pinch Block Version- Start with the action closed and the hammer down.Pinch the tab at the far end of the magazine tube with thumb and forefinger and pull the magazine tube up and out of the receiver. It will snap over a push button to hold it out. Now move the pump arm all the way forwards so the end that is normally inside the receiver is clear.

Unscrewing the barrel-

Grip the forearm and barrel in the left hand and the grasp the receiver in the right.

Unscrew the barrel by rotating the right hand down and away from you and curling the left hand up and toward you. It’s a left-hand thread.

If you are struggling to get the barrel loose, you can loosen the locking nut slightly. The nut is the ring with the screw in it that is at the very front of the receiver. Loosen the screw and with a brass (or plastic) drift, GENTLY tap it on the side opposite the screw head to loosen it.

Now the barrel should come off with no problems.

Set the assembly aside where it won’t be a hindrance for further operations; we’ll go through magazine tube disassembly and cleaning further down.

Removing the Stock

Pull the large stock retaining screw out of the receiver tang. Now strip the stock off the receiver in a straight back pull, in line with the tang angle. If the gun has never been disassembled the screw could be VERY tight.Use a little Break Free, WD-40 or equivalent on the threaded end. The hole is on the bottom side of the receiver behind the trigger guard and closest to the end of the tang.

Trigger Guard

The hammer needs to be down against the firing pin for this step.

With the receiver lying down on its right side with it’s bottom toward you and the front to your left, pinch the main spring toward the bottom of the gun to clear the hammer roller and push it down and out from under the hammer.

Roll the receiver over so the right side is up and remove the hammer pivot screw. The hammer can be removed or it can stay; its up to you.

Roll the receiver back to the left side up.

Loosen the recoil block screw a couple of turns; don’t remove it yet. The recoil block screw is forward of the hammer pivot screw and behind the front trigger guard screws. It has a head on it that is of similar size to those just mentioned.We loosen it so the frame is not pinching the trigger guard making the guard easier to get out. If you remove it, the recoil block parts will fall out and you won’t get a visual of how they go back together.

Now remove the two forward trigger guard screws. There is one on the left and one on the right, directly opposite one another.Now pull the trigger guard out the bottom of the receiver.

The hammer will fall out the bottom at this time.

Inspect the sear surfaces for wear or damage. There are three.

· Lay the receiver on its right side with the bottom toward you and the front to the left.

· Superimpose the hammer over its home position and rotate it back to full cock. The secondary sear ledge is toward the top of the hammer radius.The safety notch is at about 9 o’clock and the primary sear ledge is at 4 o’clock.

· On the primary and secondary sear ledges use a non-scratching scraper and make sure the inside corners are not full of gunk so that the sears (yes, that’s plural) can fully engage on their appropriate ledges. Also check to be sure there is no damage to these surfaces. They should be bright and shiny with no chips, dings, etc.

· Check the safety notch and make sure there is a true notch and that the catch that holds the trigger sear is not broken off. Scrape any gunk out of the notch if needed.

If any of these three surfaces are worn or damaged, get a new hammer! Unless you know exactly what you are doing do not attempt to adjust sear angles or any other alterations to the hammer.

Remove the screw holding the main spring to the trigger guard and inspect the main spring for damage.

Polish it up with steel wool and check for pitting. If there are any rust pits it is best to replace it. Surface stains won’t hurt anything. Feel free to polish the rust away with 400 or 600 emery cloth with a little water to float the fines away. CAUTION: ALWAYS, polish flat springs in the direction they are bent, NEVER across the bend. If you scratch the spring in the direction of bend it’s not a problem. If you scratch it across the bend, the scratch will act as a stress riser and the spring will prematurely fail.

Inspect the trigger sear surface. The trigger is a one-piece unit. If the sear surface is damaged, get a new one. A small pin that is easily driven out holds it in place. While looking at the trigger guard assembly check the trigger return spring for pitting or rust too.

Recoil Lock

The recoil lock mechanism is now visible by looking in the bottom of the receiver.There are three different types that I am aware of:

The OLD style with an integral locking lug hook and one leaf spring,
The IMPROVED style that has a toggling hook and two leaf springs, (one on the hook and one on the block);
The NEW style that has a toggling hook and coil spring driven plunger in the block and no springs on the hook.

The OLD style and the IMPROVED style both use a plunger button up near the hammer, on the right side, to manually disengage them. The NEW style uses a long leg on the hook toggle to disengage it. The leg sticks out the bottom of the receiver just forward of the trigger guard on the right hand side.

<>Pull the screw that holds in the recoil block and toggle, and slide the block out, notice that the hook goes to the rear.If any of the leaf springs are missing they need to be replaced before reassembly. The springs are easily cut from coping saw blades with the teeth ground off.

Set the block over a hole in a piece of anything for an anvil and tap the new spring into the retaining notch. The new spring will drive the broken one out.If there is any rust inside the action or on the springs you may want to change the springs while you in there.

Unless the manual unlock plunger on the two older styles is stiff in the frame there is no reason to pull it out. Give it a drop of oil and let it be.

Inspect the hook end of the action lock. If it is battered and abused change it out for a new one, if you can get it. It is totally acceptable to replace the OLD style with the IMPROVED style. It is also possible to exchange the IMPROVED style inertia block for a NEW style to eliminate one of the leaf springs. If you can’t get a new one, clean up the one you have as best you can. Do not remove any material from the underside of the hook. (If you get a new hook you may need to take a file swipe or two for final fitting so it locks properly) Polish the sliding surfaces lightly with a smooth Arkansas stone if you wish.Also polish the side of the recoil block that rides against the side of the receiver.

There is a spring-loaded cam in the inside face of the recoil block. This cam is what catches the recoil block when the gun is fired and allows the action to open.The mating catch is on the shell carrier. Under recoil the inertia block stays still and the gun jumps back. This movement unlocks the hook from the underside of the bolt lock and forces the cam to snap over a catch on the carrier. When the action is opened and the carrier moves down to pick up the next shell the cam is released from the shell carrier and the spring on the bottom of the inertia block resets it and the hook to home position.When the action is closed the hook snaps into its catch on the bottom of the bolt lock.

The cam is removable with a small punch and hammer applied to a pin. If it is sticky pull it out and clean the hole and the OD of the cam. While it’s out, lightly polish this face of the recoil block too. Remember, you don’t want to remove material when polishing so much as remove 100 years of grime and varnish and other gunk.

The recoil block mechanism is in there to prevent the gun from opening without manual intervention incase of a miss fire. The idea is this; the shooter gets a misfire, and can’t open the gun because the recoil-operated lock hasn’t disengaged from the bolt lock.The shooter has to disengage it manually to open the breech. This is so the shooter has to think about what they are doing and give the shell the prerequisite 30 seconds to sit before being ejected. (Like that will ever happen in Cowboy Shooting). While this mechanism can be removed from the system and nothing horrible will happen, I strongly suggest you leave it in. It is needed to perform one of the safety checks before use. See the section on Safety Checks.

As a side note on this device; it requires a minimum of a 2 ½ dram load to make it function. The Winchester Low Noise/Low Recoil shells work fine. A minimum International Skeet load will also make it function as designed. Don’t lighten the springs in an attempt to make it function with lighter loads.The springs won’t have enough power to lock the hook over the locking lug and hence it could become a safety issue.

The Carrier

The carrier pivot screw is on the left side of the receiver. It passes completely through the action and you can see the hole the screw threads into on the right side. It will probably be very tight.

After removing the screw, roll the receiver so the carrier is up.

Lift up on the tail that you just pulled the screw out of, and slide the carrier to the rear of the action to free its cam track from the cam stud on the locking lug. When it is replaced, you need to reverse this so the cam stud enters the cam track and then the tail goes down into the action where the pivot screw retains it.

Fully inspect and scrub the cam track spotless.If there are any cracks in the walls or any bulges, replace it if possible. As long as the cam stud moves smoothly through this track it’s OK. I use a drop if Moly-Grease in the track to help smooth the action.

Pull the screw in the upper slot of the carrier and remove the Carrier Shell Stop. It looks like a flat spring with a 90 degree foot bent into it. (If you have a 42 or 42A, there is no spring).

The screw will be very tight.

Plan on holding the carrier in a vice. Place pieces of wood, or plastic, block on the sides so you don’t press a bur into the cam track.

Lean real hard on the screwdriver, or back up the part with a block of wood and use an impact driver.

Scrub the slot and the inside of the carrier with an old toothbrush. Make sure the slot the spring sits in is free from rust and is smooth on the side walls.

Lightly stone the sides of the carrier and scrub the inside of the receiver where it rides with steel wool. Don’t remove hardly any material; just ensure there are no sharp protrusions that would make the carrier sticky in operation.

If there is any rust on the shell stop it would be best to replace it. This is the only thing that keeps the shells in the magazine while the action is closed.If it breaks you are stuck with single loading until you get a new one. If the rust is just on the surface and it can be polished out, feel free to do so.Remember the warning on polishing flat springs.

The spring should look like an L with the long leg inside the carrier and the short leg hanging over the front.

The leg should be square across the protruding end with no chips missing.

The front of the short leg needs to be shiny and free of anything would drag on the cartridge heads as the carrier comes down to pick up a new shell.

The backside has a steep ramp that should also be smooth and shiny to make it easier to load rounds in the magazine tube.

When replacing the spring into the carrier coat it lightly with grease to prevent moisture from getting trapped between it and the carrier.

Secondary Sear and Bolt Removal

The secondary sear is one of the primary safety devices to ensure the gun doesn’t fire from an unlocked breech.

Look in the action from the bottom, back toward the tang you will see a small (.125” wide x .375” long) toggle block. This is the secondary sear. You will notice that its top (remember its top forward edge is actually down toward the table) is being pushed on by the locking lug in the bolt.There is a flat leaf spring that is on the side you can’t see that engages it with the hammer when the bolt is all the way to the rear. When the locking lug goes into battery it pushes on the front of the secondary sear and releases the hammer to set it against the primary sear on the trigger.

Read section on Safety Checks.

Before removing the screw that holds the secondary sear we need to release the pressure placed on it by the bolt’s locking lug.Push the firing pin forward with your right index finger.

While the firing pin is forward, push down on the rear of the bolt’s locking lug. The lug will make a “click” sound and rotate into the bolt body, and the tail (sear end) of the secondary sear will lift away from the frame. If it doesn’t, the spring is broken and will need to be replaced. If you wish to observe the action of the secondary sear, push down on the front of the locking lug and the rear will come up and push on the secondary sear.Then repeat the above steps to retract the locking lug.

With the bolt unlocked, hold the receiver in your left hand with the right side facing away from you and the top up.

Use your right hand to slide the bolt back out of the receiver. (The 17’s and 26’s can use the pump arm to slide the bolt back)

When it comes to a stop, give it a slight twist down and away from you while pulling to the rear. The bolt assembly will come right out. Set it aside, we’ll come back to it.

Pull the screw that holds the secondary sear from the right side. It should, at this point, be the only screw left.

Tip the receiver so the top is up and secondary sear will fall out. As mentioned earlier if the spring is broken, replace it, or you may want to replace it just for good measure.

Receiver Shell Stop(s)

If you have a 42 or 42A you have 2 shell stops.All others (that I am aware of) have a single shell stop.

Set the receiver on the table so the bottom is up.

Look down on the receiver and you will see a small diameter hole with a screw head below the surface of the frame on the left edge up near the front. If you can’t see the screw head, clean out the hole.

Using a small screw driver, you may have to grind one to fit, pull this screw. It is threaded on top and has a long straight unthreaded portion that passes through the shell stop(s) and into a bearing hole on the far side. If the spring(s) is broken, you will need to buy a new stop or stops. They are riveted on and there is no way to replace them. If you need a new one it will need to be fitted.

E-mail me if you have to get a new one and I will walk you through the fitting.

The Receiver

The only loose part not removed yet is the ejector.If you can wiggle it out of its recess do so.Don’t break or bend it if it doesn’t want to come out. If the spring is broken then you need to replace it.

At this point the receiver is completely stripped. If it is really dirty soak it for a few hours in Hoppes #9, throw the bolt assembly in the bucket too.

After soaking, go completely through the receiver with brushes, picks, scrapers, whatever is needed and total de-gunk it.You will find saw cuts and crevices that you may never have seen before now. Make sure to get them all cleaned out and the whole inside spotless.

Go over all the inside corners toward the tang with a needle to look for cracks in the back wall where the locking lug rests during firing. Poke, prod, and scratch the needle tip around like a dentist looking for cavities.There is a product available at welding shops that is used to look for cracks. It is a three-step process including an aerosol cleaner, a penetrating die and a developer. I’d say it works great, but I haven’t found a crack in any of my guns. If you find a crack, sorry, but the old girl is nothing but a parts gun. Which isn’t all bad, parts can be hard to come by. E-mail me; I just might be interested in it.

Bolt Assembly & Locking Lug Inspection

To disassemble the locking lug from the bolt body you have to pull the pivot pin that holds them together. It is found in the right side of the bolt, just about in the center. If you have an early 1898 it will have only one screw in the side of the bolt body.All other variants have two. For the older ones pull the single screw out of the bolt body.

For the newer ones, pull the screw that has the full diameter, it is a lock.It’s a little tiny thing, be careful not to lose it.

Now push the other “screw”, really a pin, out from the other side. The slot is there so you can line it up for installing the keeper lock.

Inspect this pin for compression marks that would indicate movement between locking lug and the bolt. If the marks are too bad or the pin is sheared you may have some head spacing problems. I have never had to replace this pin but I have heard of others needing to. The pivot pin is not a load-bearing member of the action, it is purely a pivot for the locking lug. The only place that can be built up to correct this head space problem is the front lower edge of the locking lug. Have a gunsmith do this if you can’t, don’t even think about doing this yourself unless you know exactly what you are doing.

DO NOTHING TO THE LOCKING FACE IN THE REAR.

Under firing the bolt will set back against the forward face of the locking lug that transfers the energy of recoil into the rear of the frame. In a perfect situation the locking lug will be touching the backside of the bolt face and rear of the frame simultaneously before firing so there is no movement relative to the bolt body and the locking lug.Obviously there has to be some tolerance there or the gun would never lock up due to friction between the parts.

After the pivot pin has been removed, grasp the leg attached to the locking lug, depress the firing pin and pull the locking lug out of the bolt body.

Clean all the surfaces on the locking lug thoroughly.The sides where it rubs on the bolt body can be lightly stoned without harming anything.

Scrub the inside of the bolt body with steel wool.

There is a cam groove in the leg on the locking lug, up front, that the pump arm uses for cycling the action and locking/unlocking the breech. Check this groove for excessive wear. Excessive wear would be ragged edges, raised burrs, and obvious galling.

If the top of the groove is badly worn, where it dead-ends, the action may have trouble going into battery. See comments in Safety Checks.

Here’s the bad news, these are virtually impossible to get if you need to replace it. Look for parts on the Internet auctions, buy a parts gun, or rebuild it.

Opposite this cam groove is the cam stud that drives the carrier. Visually check it for roundness. It doesn’t need to be perfectly round, but the closer the better.

On the bottom of the leg that holds the cam groove and the cam stud are two compound angels. Stone these smooth to help the shell stop slide past. Don’t alter the thickness or the shell stop may get in the way of releasing shells onto the carrier.

On the right rear corner of the locking lug there is a cutout the recoil operated unlock hook uses to keep the action closed until the gun has fired.

Clean and scrape this out. Check the horn that sticks up from the top of the recoil lug at the back in the center. This is the firing pin block to prevent the firing pin from moving unless the locking lug is down and in battery. Make sure it hasn’t been altered, (shortened) or that it isn’t battered up from the firing pin striking it.

If the firing pin has struck it, it means at some point in time the locking lug was not in battery and the secondary sear was not working when someone tried to fire the gun. I haven’t seen this yet, but that doesn’t mean it never happened.If the horn has been altered you need a new locking lug or have the old one welded up and re-fit. Have a gunsmith do this if you can’t, don’t even think about doing this yourself unless you know exactly what you are doing. See comments in Safety Checks.

On to the bolt body. Unless you are changing the firing pin or its spring there is no need to pull the firing pin out.

If you need to, the retaining pin is in the back and needs a punch and hammer. On the inside front edge is a spring loaded plunger. This is what went “click” when the locking lug was manually unlocked.

Unless it is sticking, just put a drop of oil on it and forget about it. If it’s sticky, drive out the retaining pin and clean the OD of the plunger and the ID of the hole. If there is rust in the hole, change the spring too.

Oil the plunger and reassemble.

Extractors- Normally you wouldn’t need to pull the extractors unless you are experiencing extraction or ejection failures. The tightness of the outside extractor can have a lot to do with how well the shells eject.The extractors are put in with a couple of different methods depending on the age of the model.

Early Models- Model 1898, and first year 19’s and possibly anything else made prior to 1907, use a vertical pin through the outside (main) extractor and a flat head screw in the face of the breech to retain the inside extractor. I have never been able to get this screw out of mine so I don’t know what is back there. The inside extractor is really just a pusher to keep the shell rim under the main extractor.

Late Models- the extractors on all other models (that I am aware of) are both held in with vertical pins that need to be driven out.

If this is the first time the gun has ever been apart it’s a good idea to pull the extractors and scrape out the holes they are in.If there is built up oil varnish or powder fouling between the extractors and the bolt body they can’t grip the rim as tightly as they should and will give you extraction and ejection problems.On the new models the inside extractor has a slightly rounded hook to grasp the shell, but also let it slip past when the ejector strikes the rim from behind.

It is in a slot and appears to be an extension of the left guide rail. There is a small coil spring under the back end (behind the pivot pin) that keeps pressure on the shell rim. If possible replace this spring; it will help with extraction problems.

The outside one (on all models) is a sharp pointed hook.It is in a hole that needs to be scraped out with a stiff wire and flushed with solvent. The outside extractor has an attached flat spring that is replaceable.

If you need to replace it make sure to get the bends correct or it won’t fit back in the hole.

If you are dressing any burrs off these items do not remove any material from the underside of the hooks where they bear on the rim.

To sharpen a worn outside extractor, stone dress the angled ramp that allows it to snap over a chambered cartridge. Don’t go too far or it won’t have enough reach to get a good grip on the rim. If this occurs you will need to remove a small amount of material from the inside leg of the extractor where it bears against the bolt body in the hole.Generally you want to avoid this as it will weaken the extractor.

Magazine Tube and Barrel Assembly

Push Button Style-

Push in the button that is holding the tube forward, be careful when you push this in, the tube is under spring pressure and may want to launch itself off the barrel lug.Ease the tube back toward the barrel threads to expose the lug screw.

Pull this screw and then lift on the end cap to free it from the barrel lug. Remember the spring tension! You don’t want to launch this across the room.

Pull the tube out of its alignment ring toward the muzzle end of the barrel. Be careful of the pump arm, don’t bend it.

Pinch Tab Style-

Push the button that is holding the tube forward and ease the tube under spring tension back toward the barrel threads.

Look in the button’s hole and stop when you are over a small lock screw that is retaining the large barrel lug screw.Pull the little screw out.

Now let the magazine tube slide completely down to home position and remove the barrel lug screw.

Pick up on the muzzle end of the magazine tube to clear the boss on the barrel lug, and pull the magazine tube free from the alignment ring toward the muzzle end. Be careful of the pump arm, don’t bend it.

Now remove the two small screws opposite one another that retain the pinch tab unit. Remember, everything is under spring pressure.

Pull the pinch tab unit out, the pinch and the lock will come out together.

Remove the magazine spring and the follower.

Thoroughly clean the inside of the magazine tube and lightly grease the spring. I scrub the inside of the tube with a wad of steel wool on a dowel, make it shine.As far as greasing the spring, use a rag about 4” square, put a dollop of grease in the middle (about the size of a marble) and thread the spring down through the grease and through the rag.As the spring picks up grease the rag wipes it off, leaving a nice light coating.

Be sure to also clean and lightly lubricate the follower.

Lubricate the pump handle’s sliding surface on the magazine tube. A couple of shots of WD-40 work good for this. You may also blow some gunk out of there. If you do, keep spraying the WD-40 to it and wiping off the gunk.Eventually it will run clean.

Reassemble the barrel and magazine in reverse order.

Notes on Reassembly

I am not going to give a blow by blow description on how reassemble the shotgun. It is pretty basic if you were paying attention to the tear down. I will however go over some of the sticky spots that will make you scratch your head and wonder what is going wrong.

Models 17 and 26 Specifics:

When putting the bolt back into the 17 and 26 the pump arm must be back.

You will need to move it forward and back a little to find the cam groove in the locking lug.

When the cam stud on the pump arm and the cam groove line up, the bolt will just drop in.

Put the secondary sear in before the bolt.

When the pump arm pulls the bolt forward, it will automatically lock into battery.

Other Models and General

Don’t forget to put the ejector in the receiver before the bolt assembly.

Make sure the locking lug is “up” in the bolt body and the back is not sticking down.

Put the secondary sear in after the bolt, but before it gets locked into battery.

Lock the bolt into battery by pushing on the front of the locking lug before putting the carrier in.

When installing the recoil lock, don’t tighten the screw until the entire gun is reassembled or it will pull the frame sides together and you won’t be able to get the trigger guard in.

Aligning the hammer pivot screw, the hammer hole, the trigger guard holes and the frame holes can be a trick, resist the urge to use a hammer. When they all line up, the pin drops in clean. It will help if you push the hammer down and forward slightly.

General Notes on Models and Other Things Not Mentioned

If you get to this point and decide you are really not ready for taking your Marlin apart, that’s fine. Take it to your favorite gunsmith and give him this paper too. There are very few smiths around that know anything about the Marlins, and maybe this will help him get acquainted with the ol’ girl before he starts in on it.

Avoid the following models for competition, 1898, Model 19 and early production Model 17’s and 21’s. The original 1898 is typically going to have a short chamber (2 5/8”) and most are only proofed for black powder.

All the above models are missing a manufactured feature that is found on every other model that I have looked at. This feature is a tongue that protrudes out the left side of the locking bolt and engages a groove in the receiver. This tongue prevents the locking bolt from going into false battery when the action is opened very quickly; and then the pump arm is snapped forward very quickly (Like in competition).

At high speed the locking bolt’s momentum snaps it down and into a false battery outside the receiver, the pump arm disengages from its cam track and you are stuck with an open breech and no way to close it in a hurry.

If you have this happen to you, this is how you get out of it.

Push the pump arm back down and watch inside the open action for the pump arm cam lug to enter the cam slot on the locking lug.

When it enters, depress the firing pin with your right index finger and pinch the locking lug back up into the bolt body with your thumb and middle finger.

The 19G, N, and S are all OK from what I have seen as are the 24, 26 and 30. The Marlins are fast, quick handling and a joy to shoot.They are smoother than the ’97, but not as nice as a well used Win M12.

The Model 42 and 42A are my favorite for competition. Because these don’t have the carrier mounted shell stop you can slide a round into the magazine tube before closing the breech. I can load two almost as fast as a double barrel, I can discharge it just as fast and it automatically empties itself. This model will positively run circles around the Win ’97.

Here’s the tricky part. You can get parts but you have to know what is interchangeable with other models because no one lists parts or the 42’s. For example the shell stops are interchangeable with the model 31 hammerless Marlin shot gun. The pump arm is also interchangeable with the hammerless models but any other one can be altered to work with a milling machine.

Because of the age and the metallurgy of when they were built, stick to target loads.

I shot all one season with 3 ¼ Dram field loads with no adverse affects, but my 42 was built in 1922. Most of the other models were built between 1905 and 1916. Today I shoot 2 ½ dram international skeet loads. Its cheaper on components and it doesn’t beat the gun or me up.

Contact Information

rusty42marlin@yahoo.com
Rusty Marlin SASS #33284
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