Military Crimp....Why?

[stonehenge69]

I just spent the afternoon prepping LC brass.
While going through the motions, it got me thinking, just exactly what is the advantage of the military crimp?
Does it make it more water tight? More stable under the rough conditions of war?
Inquiring mind(s) want to know.




Thanks.

 

[blicharski]

i read something about military crimping because of magazines? or magazine setback?

 

[ranger335v]

Are you refering to primer or bullet crimps?

Actually, both were to keep things together in full auto weapons.

 

[nhlivefree]

I beleive it is so the primers do not vibrate loose under rapid or full auto fire.

 

[stonehenge69]

Primer crimps.
Sorry, I should have been more clear.





Trey

 

[Exposure]

Crimped primers are to prevent a primer being blown out of a case and getting jammed up in the action of a fighting weapon.

There are enough things that can go wrong in a gunfight to begin with. So decades ago militaries the world over figured it was easier to just crimp the darn things in place and prevent stoppages from blown primers.

 

[Walkalong]

It is to keep the primers from backing out and causing problems in full auto fire. Jamming, miss fires etc. It does not seal the pocket. That is accomplished with a sealant.

 

[moosehunt]

Simple! I'm fairly confident that it is a stunt intended purely to be a pain in the ass to reloaders!!!!!

 

[Redneck with a 40]

Its so the primers cannot back out of the pocket under recoil and jam full auto machine guns. Simple as that.

 

[jpwilly]

^^^ Yip and if you think it cannot happen your wrong. I had a primer fall right out of the case after firing last range session. The ammo was factory new and the primer pocket was just a bit oversized.

 

[ArchAngelCD]

When you are hunting and a primer fails because it's not seated correctly or it moved a little or backs out when you fired a previous round, you lose the animal you were going to shoot. When it happens in war and what you were aiming at also has a gun, you lose your life. That's why military ammo had crimped primers.

 

[Slamfire]

Crimped primers are to prevent a primer being blown out of a case and getting jammed up in the action of a fighting weapon.

Highpower shooters who use the AR tend to load very hot loads. Cannot tell anyone the number of times I have helped disassemble AR's on the firing line, because a blown primer has jammed between the bolt carrier and the upper.

I remember one year being squadded next to an AMU shooter on Rodriguez Range, Camp Perry. I told him I thought their ammo was too hot. He wanted even hotter ammo.

At 600 yards, he had taken off the lower from his rifle and was pounding it on the ground, trying to dislodge the primer.

When he got his rifle assembled, got back into position, his next shot was an eight. The wind had changed. For him, at his level, he had just wasted a day at the range.

This is 2007 Camp Perry brass I picked up from the Service Rifle Teams. About the only thing holding these primers in is the crimp.

Their loads are too hot!

AMU Brass



USMC Brass




I don't load that hot, so I don't need a crimp.

 

[Grump]

It was specifically developed for full-autos, largely because of the HUGE problems that come from a backed-out primer that gets slammed into the chamber at high speed.

Such true slam-fire events, before the bolt is locked, can destroy not only the weapon, but the firearm/mg that highly-trained weapon is using. Troops don't come cheap!

 

[moosehunt]

I wonder about the full auto explanation. They were crimping '06 ammo before the '06 auto (machine gun) was in much use. It existed, yes, but back then, I wonder if it was in use enough to be the factor? Just wondering.

I don't know what kind of rifles Mr. Slamfire was talking about, and can't say regarding these new "black" rifles that seem to be all the currunt rage, but in a good bolt action, a crimp doesn't mean anything regarding holding the primer in. The bolt face will hold it in as long as the load doesn't blow up the whole damn reciever.

 

[rcmodel]

They were crimping '06 ammo before the '06 auto (machine gun) was in much use.

I don't know about that.

They were crimping 45-70 and 30-40 Krag primers for use in Gatling guns before the 30-06 was invented.
The 30-06 Lewis MG was in wide use in WWI in aircraft & ground roles as well.

Before the war was over, the Browning .30 MG and BAR were standard issue.

Blown primers falling out of a bolt-action Springfield is one thing. More a nuisance that in all probability won't get you killed.

Primers falling out of an M-1, or M-16 can end up in the trigger housing and can stop a rifle cold in it's tracks.

rc

 

[moosehunt]

No disagreement there, Mr. Model. Since I don't shoot autos or semi-autos, just commenting regarding bolt guns. Unless some significant "civil unrest" devlopes here in the USA, I'm a little long in the tooth for combat situations!

 

[DBR]

When a military spec rifle (generous chamber dimensions to allow for dirt) fires an uncrimped primer actually backs out of the pocket somewhat and is then slammed back into the pocket as the case recoils and hits the bolt face. If the extractor loses its grip on the case rim the primer may come out all the way and end up in the action The crimped primer is intended to help prevent this particularly on M4 carbine type weapons that extract at higher chamber pressure than the original Stoner design 20" rifles.

Also, military ammo is generally loaded to higher pressures than sporting ammo and may be subjected to extreme temperatures either in the chamber or from the environment that can have effects on pressure. The crimped primer gives some insurence that ammo won't malfunction under such conditions.

 

[Bart B.]

DBR claims:

Also, military ammo is generally loaded to higher pressures than sporting ammo.....

Where do you get that idea? 'Tain't so according to arsenal specs for military ammo and SAAMI specs for sporting ammo when the same round's compared.

Be sure you're comparing apples to apples; same pressure measuring method. Copper units of pressure (CUP) are on a different scale than pounds per square inch (PSI) from piezoelectric strain gage systems. 50,000 CUP is approximately 57,900 PSI.

Handloaders often (usually?) make ammo that's got more pressure than SAAMI specs.

 

[DBR]

The Quickload SAAMI pressure table gives 53,664 PSI for Rem 223 and 58,740 PSI for NATO 5.56. I don't think the military has a 223 per se. These are both PSI.

The military uses a different pressure measure method than SAAMI and their results are different.

If you think this is in error, please show me.

It is also generally acknowledged that NATO ammo such as Lake City is hotter than sporting loads. I know my NATO ammo is.

 

[Carl N. Brown]

I cleaned some surface corroded Lake City arsenal 5.56 / .223 by dumping it in a bucket of hot soapy water, letting it soak six hours, then scrubbing the cases with a stiff wire brush as recommended in the memoirs of an old regimental surgeon. Then setting them to air dry. All have fired so far. Military crimped primers (and case mouths sealed with asphalt) tend to be waterproof and robust under harsh handling.

 

[rcmodel]

But it's not the crimp that made the primers waterproof.

It's the red lacquer sealer they use on GI ammo when they seat the primers.

rc

 

[Vern Humphrey]

They were crimping '06 ammo before the '06 auto (machine gun) was in much use.

'06 primers were not crimped until after WWI. Garand's first design used a primer actuated system -- the primer was supposed to blow out a bit and unlock the action. When the Army went to crimped primers, he had to go back to the drawing board.

 

[moosehunt]

Mr. DBR, I don't buy your statement about primers backing out, then being slammed back in when the case recoils. Upon firing, the case expands to chamber size (actually a skosh more, because the chamber expands a bit, too) and grips the chamber walls. After the preasure drops, the case contracts (significantly more than the chamber) and can then be extracted, but the preasure is gone by then. If the case moves back, it does so before the preasure rises and stops at the bolt face and doesn't go back forward. I beleive someone is blowing smoke up your hiney on that!

 

[Slamfire]

Mr. DBR, I don't buy your statement about primers backing out, then being slammed back in when the case recoils. Upon firing, the case expands to chamber size (actually a skosh more, because the chamber expands a bit, too) and grips the chamber walls. After the preasure drops, the case contracts (significantly more than the chamber) and can then be extracted, but the preasure is gone by then. If the case moves back, it does so before the preasure rises and stops at the bolt face and doesn't go back forward. I beleive someone is blowing smoke up your hiney on that!

The primer does back out. The front of the case expands, gripping the case neck to the chamber. Then the case stretches to the bolt face and stuffs the primer back in the pocket.

If you are firing a light load, one that does not stretch the case to the bolt face, you will extract cases and notice that the primer is sticking out.



I came to this conclusion after examining case heads on lubricated cases. Primers on dry, unlubricated cases were flat. Same load, same gun but with lubricated cases, the primers were rounded.

I puzzled over that, and realised that on the dry case, the case was stretching and stuffing the primer back in the pocket. On lubricated cases the whole case and primer moved back to the bolt face at the same speed.

Since then, I not only use a chronograph to develop rifle loads, but I lubricate the cases. The transition from rounded primers to flat primers is clear, and that tells me that pressures are starting to go up.

 

[Vern Humphrey]

Mr. DBR, I don't buy your statement about primers backing out, then being slammed back in when the case recoils.

He is 100% right. The primers back out before the powder ignites.

The phenomenon is more pronounced in revolvers, which require a bit more headspace to make sure the cylinder can rotate freely. That's why primer backed out, coupled with a sooty case is a sign of low, not high pressure in revolvers.