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Slam Fire

3K views 14 replies 11 participants last post by  coz 
#1 ·
Reading my new Speer manual #14 p36-37 about slam fires on AR type rifles. In looking at a normally seated primer as a source of slam fires, I was interested in thoughts of those that reload and shoot lots of 223's in AR platforms.
Speer states: A slam fire can occur even when primers are properly seated. Many AR's have no firing pin retractor and the firing pin is quite heavy. The inertia of the firing pin may cause it to snap forward as the bolt closes, firing the cartridge. If the bolt is not yet fully locked, the case can rupture, potentially damaging the firing pin and/or injuring the shooter. Military primers are less sensitive than commercial primers to address this potentially hazardous condition....no primer can provide 100% protection against slam-fires if the loader doesn't seat the primers deep enough, or rifle has a headspace problem or an out-of-spec firing pin. It spoke of CCI military style primers for 5.56....for an excellent dissertation on slam-fires and solutions, Speer referred to "The US 30 Cal Gas-Operated Service Rifle - A Shop Manual by Jerry Kuhnhausen also found on www.gunbooks.com."
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Rather than assume, since the same 5.56 cases are resized and reloaded for 223. Would those primers for the hotter load of the 5.56 work fine for the 223 AR?
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Looks like there are two volumes in the book at $47. Amazon has it at $40 but it looks like 30 cal stuff (M1, M14 stuff). Not sure how much of this book theory crosses to the 223 AR platform. May be those who have the AR in 223 can refer to an equivalency book that address the same issues.
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Any thoughts on the Speer information?
 
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#2 ·
My first thought is that Speer/CCI makes the harder "military-style" primer, and sells them to the civilian market, and they cost MORE than regular primers. Why would people spend 50 dollars a thousand on mil-spec primers if 35 dollar a thousand CCI400s would work. But SLAM-FIRE!!!!!!!!! Oh My God. Need to buy the mil-spec primers.

My second thought is, if that really is possible with an AR, I'm sure-hell glad I have a Mini. ARs are just too damn dangerous to own.

My third thought is "use a lighter firing pin, and add a spring (like most semi-auto bolts have)".
 
#7 ·
The firing pin doesn't stick out far enough to set off the primer until the bolt is locked, sounds like some people had high primers that were set off by the bolt face and just thought they knew what caused it. Just saw a post on FB of an out of battery on an AR where you could tell that the cartridge was almost 3/16" out of the chamber, no way it was an actual slam-fire. I use 41's in my reloads as they are the same price where I buy them anyways.
 
#8 ·
Thanks everyone for your comments. Good to know. I made a bunch and they shot up ok but I did NOT have the CCI #41 primers. While it sounds ok and it worked out for what I used. I like SteveM comment about cheap insurance. 41's are about close enough the same price as the others I bought so I will convert to them just to be sure.
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After reading SteveM comments I looked up the CCI #41 and here is one of the pages:
http://www.midwayusa.com/product/1301170074/cci-small-rifle-military-primers-41 $37.99/1000
Product Information
Number 41 Mil-spec primers are made to the same specifications of the U.S. Military and reduce the chances of a slam-fire. While designed for you in Military-style semi-auto rifles, they use the same data as CCI magnum primers.
 
#10 ·
I have never had a slam fire either. I usually load my .223's with CCI #400 SRP, or Tula KVB223's. Both have worked outstanding. I haven't figured out how someone can seat a primer high on a .223 case. Mine are always .006"-.011" below the head depending on the head stamp. The Tula primers are slightly bigger than CCI, and I find they work well in cases that have pockets starting to loosen up.
 
#12 ·
I have never seen a slam fire or even read about it on the internet on an AR. But if you want safety then use the CCI 41 primers. If you have done some trigger work there may be a problem with less sensitive CCI 41 primers.

A common thing when doing trigger work on an AR is to install a lower power hammer spring. That puts less energy into the firing pin and the firing pin MAY NOT set off the CCI 41 primer. You need to test for it. Also the warning about the CCI 41 being a Magnum primer means you need to adjust your load level downward and re-do all your testing for the best load level for accuracy.

If your priming is not adjusted correctly (that done on the press) you can install primers too high or totally crush them. Make sure they are seated below flush. Hand priming can be done wrong too. My Dillion RL550B came factory adjusted for both large and small primers to the correct seating depth and I have never had to adjust either size on several different primer bars in my possession. But it is possible for a Dummy to screw it up as it is adjustable to be incorrect for primer seating depth.

I'll stick with my Winchester standard primers, thank you.

LDBennett
 
#13 ·
When someone has a reload that is a dud on the first firing and goes off the second time what is the usual suspect? They didn't fully seat the primer so the first firing pin strike seated the primer then lacked enough energy to set it off. Some how in the history of slam fires (I have done a lot of reading on it) the primer being seated too high suddenly becomes a common culprit for inadvertent detonation by a floating firing pin traveling with only a fraction of its normal force. Doesn't pass my sniff test, but it is a popular theory and has some big name proponents.

The biggest reason why there is so little known about slam fires is that they rank somewhere between the Snipe and Jackalope for confirmed sightings. When gas guns blow up the cause is often an out of battery condition caused by a faulty firearm or ammo, though these often get counted as slam fire they are not really as even a bolt gun can fire out of battery. One of the theories of true slam fire in M1/M1A style actions that is believable to me is improper bolt operation. The bolt should be released from the fully rear position and be slowed and cushioned by stripping a cartridge from the magazine. Single loading then letting the bolt go flying home over an empty magazine is to me a credible theory of what causes slam fires.

Again, not something many people have seen and the studies people have conducted are inconclusive due to the rare nature of the slam fire. It's like your health, we don't have all of the answers but we're pretty sure that if you don't smoke then you'll probably live longer than if you did. Then again, you might live to be 105.


Added note: I've often read where Federal primers were used in ammo that slam fired. No proof that it was the cause, but if a soft primer is a commonality then it makes sense to use a harder primer like WSR or CCI.
 
#15 ·
Slam fires aren't as uncommon as you might think due to the floating firing pin common to all AR rifles. The next time you eject a chambered unfired round, take a look at the primer and you'll see the firing pin mark that was created when the round was chambered. Personally, I use the CCI 41 primers because my LGS sells them for the same price as the 400's, but the CCI 450 (small rifle magnum) primers also have a thicker cup than the standard CCI 400 primers and I believe everyone sells them for the same price or very close to the same. When I asked Hodgdon (I use HP335), they recommended the use of CCI 450, CCI 41 or Rem 7-1/2 primers in AR rifles with all of their powders.
 
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