Primer Crimping

fhwiggins · July 21, 2009, 09:53 AM

Since Military Spec. 5.56 primers are crimped, I'm thinking that this is due to the increased pressure and the crimping is designed to prevent the primer from backing out. My question is that if I am trying to reload as close to the military specs as I can, should I be crimping the primers. If so, where would I find a primer crimper and where could I obtain information regarding military specs for 5.56.

ilbob · July 21, 2009, 10:13 AM

Nothing to do with pressure.

It is to prevent the primer from backing out and jamming.

I think it is mostly an anachronism these days as the tolerances on the primer pocket are quite adequate to keep the primer in place. But once something gets into a mil spec, it is all but impossible to get it out.

**Mike Irwin** · July 21, 2009, 10:56 AM

It's more a necessity in automatic weapons where inertia, pressure, and the opening of the action while there's still a fairly high amount of pressure in the system could back the primer out.

As I understand it, the faster the rate of automatic fire, the more likely this is to happen.

Unless you're shooting a SAW or Minigun, there's no need for you to crimp your primers.

fhwiggins · July 23, 2009, 08:47 AM

Thanks for the information! I am just shooting semi-auto and did not want to crimp unless it was necessary to be safe!

Sevens · July 23, 2009, 08:57 AM

And if you are loading for a SAW or minigun, I highly recommend you look at a progressive press!

**Mike Irwin** · July 23, 2009, 09:50 AM

Nope, not a safety issue at all.

I have heard that primer crimping truly became a necessity and common when aircraft began to mount guns where the pilots couldn't clear jams. A primer popping out of the case during cycling has a pretty high liklihood of causing a stoppage within a few rounds, if not immediately.

I've seen several belts of US machine gun ammunition from World War I where the primers were not crimped.

July 21, 2009, 09:53 AM	#1
fhwiggins Member Join Date: July 14, 2009 Posts: 36	Primer Crimping Since Military Spec. 5.56 primers are crimped, I'm thinking that this is due to the increased pressure and the crimping is designed to prevent the primer from backing out. My question is that if I am trying to reload as close to the military specs as I can, should I be crimping the primers. If so, where would I find a primer crimper and where could I obtain information regarding military specs for 5.56.

July 21, 2009, 10:13 AM	#2
ilbob Senior Member Join Date: November 29, 2006 Location: Northern Illinois Posts: 515	Nothing to do with pressure. It is to prevent the primer from backing out and jamming. I think it is mostly an anachronism these days as the tolerances on the primer pocket are quite adequate to keep the primer in place. But once something gets into a mil spec, it is all but impossible to get it out. __________________ bob Disclaimers: I am not a lawyer, cop, soldier, gunsmith, politician, plumber, electrician, or a professional practitioner of many of the other things I comment on in this forum.

July 21, 2009, 10:56 AM	#3
Mike Irwin Staff Join Date: April 13, 2000 Location: Northern Virginia Posts: 41,381	It's more a necessity in automatic weapons where inertia, pressure, and the opening of the action while there's still a fairly high amount of pressure in the system could back the primer out. As I understand it, the faster the rate of automatic fire, the more likely this is to happen. Unless you're shooting a SAW or Minigun, there's no need for you to crimp your primers. __________________ "The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza Baby Jesus cries when the fat redneck doesn't have military-grade firepower.

July 23, 2009, 08:57 AM	#5
Sevens Senior Member Join Date: July 28, 2007 Location: Ohio Posts: 11,756	And if you are loading for a SAW or minigun, I highly recommend you look at a progressive press! __________________ *Attention Brass rats and other reloaders:* I really need .327 Federal Magnum brass, no lot size too small. Tell me what caliber you need and I'll see what I have to swap. PM me and we'll discuss.

July 23, 2009, 09:50 AM	#6
Mike Irwin Staff Join Date: April 13, 2000 Location: Northern Virginia Posts: 41,381	Nope, not a safety issue at all. I have heard that primer crimping truly became a necessity and common when aircraft began to mount guns where the pilots couldn't clear jams. A primer popping out of the case during cycling has a pretty high liklihood of causing a stoppage within a few rounds, if not immediately. I've seen several belts of US machine gun ammunition from World War I where the primers were not crimped. __________________ "The gift which I am sending you is called a dog, and is in fact the most precious and valuable possession of mankind" -Theodorus Gaza Baby Jesus cries when the fat redneck doesn't have military-grade firepower.

July 23, 2009, 08:47 AM	#4
fhwiggins Member Join Date: July 14, 2009 Posts: 36	Thanks for the information! I am just shooting semi-auto and did not want to crimp unless it was necessary to be safe!