Sticky bolt solutions

[User Name]

I've heard alot of complaints about sticky bolts from Mosin shooters around here lately. So I'm borrowing NotPC's article on fixing this problem. He is a member of another forum I visit, and I wanted to give him credit for this.

I hope this helps.


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First, I will not call this a "sticky bolt" problem, because the bolt is not sticking.

The cartridge case is binding in the chamber and either it will not rotate freely enough to allow the bolt to unlock or it will not allow the bolt to rotate on it with minimal effort.

For review, there are eight steps in the Cycle of Operation of a weapon that uses a metallic cartridge and a chamber, whether it is a single shot or a full automatic weapon. They are:

1 Feeding - either manual or mechanical
2 Chambering
3 Locking
4 Firing
5 Unlocking
6 Extracting
7 Ejecting
8 Cocking

One or more factors can cause difficulty with the unlocking phase. Some are:

1) Chamber dimensions (in spec, or under spec.)

2) Chamber machined smoothness

3) Chamber burrs

4) Chamber internal dimensions reduced from residue (powder fouling - both burned and unburned accumulation, petrified cosmoline, accumulated case coating materials, rust, etc.)

5) Cartridge case dimensions (oversized at either or all - neck, shoulder, or body) and cartridge case wall thickness.

6) Cartridge case material - three things come to mind here: the elasticity of the metal used, the "linear co-efficent of thermal expansion" of the metal used, and the co-efficient of friction between the cartridge case and the chamber; Upon firing, the cartridge case will expand radially to conform to the internal dimensions of the chamber. Brass will shrink back closer to its original dimensions than will steel - this is elasticity. Both brass and steel are alloys - that is to say that they are a mix of materials and the proportion of that mix will determine the physical properties and characteristics of each. Batches will vary. Upon firing, the cartridge case will also lengthen as it conforms to the chamber, as the internal pressure of an explosion acts in all directions. This can cause a tight wedge-like or binding fit between the face of the bolt and the shoulder of the cartridge case. Brass is softer than steel and will have a higher drag factor when it comes to rotating it in the chamber, but it shrinks more than steel. Offsetting characteristics if there aren't any extra factors introduced into the equation, like #7, coatings, which can throw a monkey wrench in the process.

7) Type of cartridge coating (usually lacquer or polymer and its formula - Does it vary from lot to lot? Yes; Does its melting/adhesive temperature vary? Yes; How much out of spec is it over time? No one knows; How fast does it build up to the point of interfering with unlocking? Varies with the individual rifle.)


As some rifles can use coated cartridges without problems, the trouble is not universal.

Remedies:

1) Make sure that your chamber is absolutely clean and free of any residue. It may have to be thoroughly scrubbed by using lacquer thinner and a 20 gauge shotgun brush driven by an electric drill. I recommend stopping at 30 second intervals and cleaning out the trash. One or two minutes time should do the job. Microscopic residue may have been compacted into the grain of the steel over a 60 year period by thousands of "50K p.s.i. poundings". Compacted residue may appear smooth and reflect light, giving the false impression that a chamber is clean. Not necessarily so. In addition, the use of "de-leading wool" wrapped around the brush is an excellent method to hasten the process. Rust removal will require a little more effort.

2) If this does not solve the problem, one may have to use copper-washed steel-cased or brass-cased milsurp ammo. Some folks use commercially available brass cases and manufacture their own ammunition. Also, some commercially-loaded ammunition is brass-cased.

Remember that milsurp ammo is surplused for a reason or reasons - possibly never to be known to us. It is cheap because it is discarded by some country as unservicable. Most of it works very well, but it is usually not factory fresh and poor storage conditions and age can take their toll.