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Why Crimp Semi-Auto Rifle Loads?

© 2014 – Ed Harris

When I was QA Manager for Ruger’s Newport, NH operations in the mid-1980’s the company had received Mini-14 rifles back in customer service having cracked right locking lugs. Usually owners would not admit to use of hand loads, because this would void the warranty. But the mechanics of the Garand type locking system being what it is, for this to occur, pressure would have to be extreme. I had lengthy discussions with Albert Cole, formerly of Springfield Armory (the US Government Facility in Springfield, Massachusetts) during development of the M14 NM Rifle. They Army investigated a few incidents of right locking lugs cracking which occurred at Camp Perry when hand loads were used in which bullets did not have mouth varnish or asphalt bullet sealant.

Therein lies the clue!

Military teams had requested match ammo to be loaded without the sealant. The reason they gave was supposedly because the sealant was felt to be a detriment to accuracy. Extensive testing by the Small Caliber Laboratory at Frankford Arsenal indicated that the sealant indeed improved ballistic uniformity and reduced metal fouling by acting as a lubricant. When the subject was pressed further, the unspoken reason for the request came out.  It was not for reasons of accuracy, that was a ruse, the real reason was they wanted to make it easier to pull the bullets!

Military teams were substituting Sierra 168-grain bullets for the M118 FMJBT bullets, making what shooters called “Mexican Match,” the moniker tagged onto the “GI Reloads” by noted California shooter and several time National Champion Mid Tompkins. 

William C. Davis, Jr., then head of the small caliber lab at Frankford Arsenal, recommended very strongly against any change in M118 ammunition for several reasons. First was the loss of waterproofing which was important for long term shelf life and was absolutely necessary for combat sniper use. 

The second, more important reason is that a real danger arises if an attempt is made to fire a round containing no powder, but having a primer only. That is because case primer blast alone is sufficient to lodge a bullet in the throat just ahead of the origin of rifling. When this occurs, there is usually no audible report. The firer may think that he experienced a short-recoil, accompanied by a failure to eject and may then take immediate action to manually cycle the rifle, eject the spent case and chamber another round and immediately fire it.

If bullets are not securely seated in a tight neck, and either asphalted or crimped, the power of an M1 Garand or M14 action spring in stripping and chambering a round is sufficient to telescope the bullet of the next chambered round back into the case. This causes extreme compression of the powder charge above 100% of load density, increasing pressure from that aspect, but also resulting in firing the rifle with TWO bullets ahead of this dangerously over-compressed powder charge. With M118 ammunition the resulting "double-bullet proof" pressure is about 80,000 psi. or about 15% above normal proof pressure. 

Testing was done at FA in which both M1 and M14 rifles were set up with a bullet lodged in the throat ahead of the chamber, so that upon chambering a standard proof cartridge, the bullet point then rested against the base of bullet obstructing the throat. Upon firing, the broken locking lugs which had been observed at Camp Perry on TRW rifles could be repeatedly and predictably duplicated. Differential heat treatment of the bolt lugs and receiver locking surfaces increased the strength of later M14 rifles, so that they could withstand this double-bullet set-up without breaking locking lugs or setting back locking surfaces to the extent that headspace exceeded field reject limits. 

M141  M142

Broken Lug on USGI M-14 Bolt…

At Ruger, customer service observed the same broken right-lug problems in returned Mini-14 rifles in 5.56mm firing suspected hand loads. Tests following the Frankford Arsenal procedures were more impressive if the case had a soft head below 170 DPH, typical of much commercial brass,  or if there was a draw scratch in the K-L regions of then head-body junction where the case is less supported.

Bottom line, if bullets are tightly seated and adequately sealed and/or crimped, enough that loaded rounds withstand 5 secs of sustained compressive force of 80 pounds "bullet push" against a bathroom scale, without measurable shortening, the rifle should then reliably jam, instead of chambering the subsequent manually cycled round. Hopefully the shooter will then recognize that something is wrong!

The concept we need to ingrain into hand loaders is that when anything abnormal happens:

Clear / Eject
Lock bolt open, 
Engage Safety,
Check bore! 

Ruger published warnings alerting hand loaders to this potential problem in its Mini-14 operator’s manual. As a result of having worked with Ruger engineers investigating this condition, Lee Precision developed and made available to shooters its Factory Crimp Die.


Lee Factory Crimp Die…

I recommend that you buy and use one of these in every caliber in which you reload ammunition for use in a semi-automatic rifle. I do! 

We are not talking accuracy here, Gentlemen, we are talking SAFETY!


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