I occasionally do work for Armament Research Service, and they recently published one of my pieces as Research Note #8, on the subject of self-loading rifle durability. Rifles, in general, are pretty durable items, with only a few elements subject to potentially incapacitating damage when in normal use. You can see my complete article on the subject in PDF format at the ARES site.
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Three further points should be made on springs in self-loading rifles: wear and ‘set”:
Self-loading rifle springs are usually guided in holes or on rods. Hole guides often wear material off the OD of springs, reducing their rate and spring force at design length. M-1 Garand operating rod spring is a case in point; a well used M-1 will usually exhibit flat spotting all the way around its OD. This leads to high bolt travel speeds which can fracture the rear of the receiver. Internal blade guides, such as used on the M-14 rifle, create comparable damage on the ID of operating springs. Internal rod guides seem to be the best practice.
Spring steels made before the end of WW II usually had high phosphorous contents and inferior metallurgical processing which leads to the spring taking a ‘set’ over years of storage compressed in an assembled firearm. This also reduces rate and spring force at design length.
The best spring steels are not ‘stainless’ and cannot be protected against corrosion with coatings due to their function, so corrosion is a common cause of field failures in self-loading rifles. Corrosion pits are both stress risers and reducers of beneficial compressive surface stresses which lead to premature breakage.
A good article. Just a FYI the UXO industry and Corps of Engineers (CoE) have simplified “ARMS” to “3Rs”. Recognize, Retreat and Report. It is easier for children to remember. I know not all the world has adopted it but it is getting there.
Other parts can fail too. Here is a thread about a gun range in Vegas that rents full auto AKs and shoots hundreds of thousands of rounds through them. http://www.ar15.com/forums/t_4_64/159106_AK_abuse__home_built_version_update_on_Page_6_.html&page=1
You are getting ahead of me – that is the subject of my post for Friday. 🙂
Sorry, but “Mainspring”, from very early single shot muzzle loaders to date, is the
name of power source giving the impact to ignite the propelling mixture in firearms terminology. Should not to be confused with “Recoil” or “Return” springs.
Considering gas-operated fire-arms: what about elements which has contact with gas? Firing powder always give residue, so it can clog gas-operated firearms, specifically if fire-arm can’t be easily disassembled to clean. On the other hand all Soviet Union self-loading rifles (and machine guns) from 1930s onwards are gas-operated and are considered reliable enough.
I think it’s safe to say that gas operating system has been found overall the best for military rifles and machine guns. There are still some recoil operated machine guns in use, but in almost all cases those are based on pre-WW2 designs (like the MG3 and .50 cal M2 HB). Delayed blowback rifles such as the CETME/G3 and FAMAS are also still in use, but they are being phased out and replaced by gas-operated rifles. Considering that reliability is one of primary design goals of military weapons, I think the proliferation of gas operation indicates that overall it is probably the most reliable system. For good designs clogs causes by powder residue seem to me pretty much a non-issue even when minimal cleaning is performed.
“pre-WW2 designs (like the MG3 and .50 cal M2 HB)”
Soviet Union widely adopted one machine gun which was not recoil-operated: KPV-14.5 (Vladmirov Big-bore machine gun), it is still used in tank variant (KPVT) in Russian AFV.
The example of CMP M1’s is interesting–but maybe not the ideal example, or at least not what one might expect from later guns. They were made by 3 companies in one country in a 20 year period. Nearly all important parts were forged, machined, and heat treated out of specific steel. There are not that many critical tolerances in the design. All parts are 100% interchangeable across all versions. A lot of bugs and failure points were worked out before full production. They were not select fire.
Don’t get me wrong, I have a 1942 vintage CMP myself, and it runs great. I’d place full confidence in it. I’m just not sure that I’d compare it to something made from a stamping, by ten different plants, etc.
Also, all of the CMP M1’s have seen some level of refurbishment with parts taken from many different rifles to make one functioning rifle.
Good point, also most of the rifles showing up at the CMP are from military units that had armorers to maintain the rifles, and when they were stored they got slathered with cosmoline.
Another point might be the extensive set of gauges available to armorers to go / no-go any shape or dimension of importance on that particular rifle.
With gas-operated firearms, there is the ever-present port erosion problem. Many parts are subject to fatigue failure, such as bolt locking lugs, sheet metal receivers and springs. Throats wear out and lead to increased dispersion and keyholing.