Check for any burrs and polish the sides and any burnished areas. Do not remove any metal or change the shape.
Place the bolt back in the action and slowly slide it back and forth. It should move smoothly through out its length. Check for any burrs on the bolt and in the receiver and polish them out if you find any. Pay attention to the slot in the side of the bolt where the ejector rides and carefully polish the slot's sides and bottom. Wrapping a small piece of the 600-grit paper around a narrow file or Popsicle stick easily does this. Carefully polish the cam on the bottom of the bolt where it rides over the hammer nose. Do not reduce the height of the cam. Polish it only.
McPherson's gives detailed instruction on how to narrow this cam to reduce the friction as the bolt rides over the hammer. This modification, in my opinion, is not for the faint of heart and should only be attempted by the advanced amateur or professional gunsmith. Bolts are not cheap should you have to replace it.
Like the objection to the two-piece trigger/sear, some object to the two-piece firing pin. Theory is that the two-piece pin requires more force from the hammer to fire the primer, especially when the hammer spring has been reduced. After market one-piece firing pins are also available. In his book, McPherson details how to modify the existing firing pin to lighten it so I will leave it at that.
HAMMER & HAMMER SPRING
Remove ¾ of a coil from each end of the hammer spring. If you use a grinder to do this, do not get the spring too hot to hold or allow the spring to change color. Go slowly and grind the cut off end flat like it was done at the factory. If you do not have a grinder, use a triangular file to file a groove in the coil and break the end off. Then file it flat. A Dremel tool with a cutoff blade will also work to remove the ¾ coil. In all three cases, do not nick the adjacent coil as this will set up a weak spot for future breakage. The hammer spring, due to its barrel shape, goes away very quickly. Should you remove too much, you will find that it will not reliably, maybe not at all, provide enough force to fire a primer. If this occurs, and you do not have a spare spring, do not despair. Locate, in your parts drawer or at the local hardware store, some small, thin washers that will just freely slip over the hammer strut. Place one on each of end of the spring and try to fire a primer in an empty case. One washer on each end will most likely provide enough power to fire a primer.
* Reduced force after market main springs are available for those who desire to purchase them rather than modifying the existing spring.
* Using the wet or dry paper, polish the hammer strut on both sides and both edges. Check and remove any burrs from the hammer pivot hole. Polish the hammer screw where the hammer pivots.
* Check the sides of the hammer for bright drag spots. A burr in the receiver rubbing against the hammer can slow the hammer fall. Remove any burrs.
Remember the 3/32" hammer over travel referred to above? Some of this can be removed by grinding the nose of the hammer down using a belt sander or fine grinding wheel. If you feel uneasy about removing metal from the hammer, skip this step. You need to remove approximately 1/32" (.031"). Filing the hammer nose is not practical due to radius and the requirement to maintain the exact contour. Carefully grind and polish the hammer nose. I do not recommend removing more than 1/32" (.031"). This will assure that the hammer is sufficiently depressed to be held at full cock. Scribe lines on both sides of the hammer nose following the same contour and remove metal to this line. A better method of assuring that you don't remove too much is to use a vernier caliper and measure from the flat on the bottom of the hammer to the nose. Go slowly, measure often and then polish the nose. Be advised that altering the hammer may void the manufacturer's warranty.
Leave the sides alone. Polish all burnished areas where the lever acts on the carrier. Look for brass colored areas where brass rubbed off and polish those areas as well. Check the screw hole for burrs and remove. Polish the screw where the carrier pivots.
Check for burrs and polish as required. Polish the cam area where the bolt pushes the ejector down into its slot in the receiver. Spring tension on the ejector can be reduced by carefully bending the spring toward the ejector. Again, an after market one piece ejector/spring is available.
MAGAZINE PLUG & SPRING
Remove the magazine tube plug and remove the 10 shot plastic plug from the spring. Replace the magazine tube plug and you can now load 13 rounds in the magazine. I don't recommend that you remove any coils from the magazine spring unless it is hard to load rounds into the magazine. If you do decide to remove any coils, proceed slowly and try often for proper feeding. Be safe, leave this spring alone.
Some people find the orange magazine follower objectionable. Its good point is that it is easy to see through the loading gate to verify that the magazine does not contain any live rounds. Some feel that the plastic follower contributes to rust forming in the magazine tube. While this may be true, a more likely reason has to do with the fact that few people remove the spring and follower and clean the inside of the tube much like they would a shotgun barrel. For those individuals with a lathe, a replacement follower can be made out of aluminum bar stock. It too is easy to see through the loading gate.
Everyone complains about the safety. However, it does have a couple of good traits. One, it allows you to safely cycle rounds through the action to unload the magazine without the danger of an accidental discharge. Two, you can dry fire occasionally without danger of breaking a firing pin.
Five things can be done to the safety.
1. Leave it alone and use it when desired.
2. Replace it with an after market dummy that fills the hole and appears as a bolt.
3. Remove the stock. Turn in the safety set screw enough to lock the safety in the off position so that it can't be applied accidentally.
4. In a lathe, face off the left end of the safety so that it is flush with the left side of the receiver when in the off position. The safety can be applied by pushing on it with the end of a pencil.
5. Remove the safety, go to your friendly hardware store and purchase an "O" ring that fits the grove in the safety. After reinstalling the safety, slip the "O" ring over the left end. This will prevent the safety from being applied accidentally.
I have fired several thousand rounds through my Marlins and have never had my safety accidentally placed in the on position.
Reassemble the rifle in the reverse steps to disassembly. Put a light coat of oil on all parts prior to reassembly. Do not tighten any screw all the way until everything is back together. Then snug up all screws. Cycle the action several times to assure everything is working smoothly. On my Marlin 1894, if the trigger guard plate support screw is too tight, the action will appear sluggish. If this occurs on your rifle, back the screw off very slightly.
Every Marlin I have observed suffers from screws loosing up during heavy shooting. The most common is the carrier screw, but the hammer screw and the trigger guard plate support screw also may loosen. Keep a screwdriver close by when shooting and retighten the screws as required. A better solution is to apply a SMALL drop of blue Loctite to the threads of these screws. Loctite can be easily applied to the threads on the left side of the receiver using a toothpick. DO NOT USE RED Loctite or you may never take it apart again.
You have now tuned up your Marlin and are ready to enjoy a great rifle.