Slam fire and primers

BeerAlchemist

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Jul 12, 2009
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Tired of paying .45 a round for my AR so I have been setting up to reload and been doing my homework. That said, the whole slam fire issue on autoloaders has me a little worried. I contacted Young manufacturing (who made my AR's bolt) and they said with .223 AR's I shouldn't worry as long as my primer is seated properly. But, I like plurality of opinion. Should I go ahead and load the CCI small rifle I have and not worry? Or should I go with added insurance and hand them off to my buddy for his bolt action and wait until I can get some of the heavier duty 41's in for the autoloader?
 

randyp

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Jun 21, 2006
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Re: Slam fire and primers

Agree with Lumpy, CCI's are good, be sure they are seated below the case head. Cases must be sized full length so they enter the chamber freely. Use of a Wilson Cart. gauge will help insure this. Cases must be kept trimmed to length for same reason. Firing pins on AR's are free floating and will dimple the primer upon chambering.

Randy
 

royboy

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Re: Slam fire and primers

ALWAYS!!!!! Have your muzzle pointed in a safe direction when closing the bolt on any free floating firing pin .
I have heard always feed from a mag. if feeding 75amax in a .223 and have to load by hand. dont let the bolt slam home,close the bolt and forward assist it.
 

Graham

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Oct 30, 2007
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Re: Slam fire and primers

Are the cases FL sized and the shoulder returned to spec? If so, you're probably OK.

A slam-fire has nothing to do with the manufacturer of the primer. FL size your brass and bump the shoulder a large amount, because the bolt force of most AR's will bump the shoulder as it chambers. Most factory chambers then blow the shoulder out a mile. So, throw the brass away after a few firings.

Then, if you are shooting a big AR (.308 case), a firing pin hole diameter of larger then .065 will pierce primers before max pressure is reached, which is also not to be mistaken as a primer problem.
 

HitEmHard

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Jun 10, 2004
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Re: Slam fire and primers

If you put a primer on concrete and hit it, it almost always slam fires.
cool.gif
OK now back to business...

D
 

BeerAlchemist

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Re: Slam fire and primers

Ok Graham, here comes the reloading newb question...how do you return the shoulder to spec? Is that a simple matter of setting up the FL die properly or is there something I don't otherwise know going on with that? From what I read slam fires occured as a result of over sensitive primers and/or too heavy pin, this is why I contacted Young manufacturing to see what they had to say. I'm shooting .223 out an Oly H-bar, so here's to hoping it doesn't "blow my shoulder out a mile."

HitEmHard, how's about shooting at a primer for better fun, then you know you hit the ten ring for sure
smile.gif
.
 

michaeltx

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Re: Slam fire and primers

Moving the should is just setting the FL die properly. For my m1a, I have to set the die so that the press cams over pretty hard.

Slam fires are rare, can happen anytime, but it's more of a perfect storm thing. As long as you seat primers slightly below the case head, and don't do anything silly like use pistol primers or let the bolt slam home on a round you put directly in the chamber, you should be fine. The 41s offer a little insurance if you want it, but not really needed.
 

mj2evans

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Aug 25, 2008
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Re: Slam fire and primers

CCI primers cups are pretty tuff, you should be fine. I used them for HP for a while before I got a supply of Wolf SRM. Now the newer gold Win are softer than the olders sivler Win and I had trouble with them (pressure sings, not slam fire). AR uses a floating FP so *always* point down range when chambering a round. Sure, slam fires are rare but it only takes one to ruin your day. As others have said just make sure you seat the primes well in the pockets.

The original SKS bolt and firing pin was designed with a spring to keep the firing pin from floating. This feature was effeventually dropped but it sure makes sense to have it.
 

Graham

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Re: Slam fire and primers

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Beer Alchemist</div><div class="ubbcode-body">Ok Graham, here comes the reloading newb question...how do you return the shoulder to spec?</div></div>You need to measure the shoulder bump. For that you need a caliper and a measuring tool. Stoney Point/Hornady offers a bullet comparator with a step-down point that hits the shoulder's datum line. Buy one from Sinclair. Don't just crank the die down until it hits the shellholder and start sizing: some factory dies size too much at that point, like beyond .005; and some thick shell holders won't give any shoulder bump at all when set to maximum travel of the press arm. The only way to know for sure is to measure it. For bolt guns .001 is fine. For gas guns I would go .002 or .003.

For insurance against slam fires make sure to seat your primers properly into the pocket so that there is a bit of a step down from the case head to the primer anvil face. You can test that depth with your finger - by feel.
 

Greg Langelius *

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Aug 10, 2001
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Re: Slam fire and primers

Never had nor saw a slamfire; have a Garand, had an AR and an M1A, and nearly all my ammunition is handloads.

IMHO the key to avoiding slamfires is to use the ammunition and firearm the way they were designed.

The ammunition was designed to have the primer seated flush or below the level of the cartridge base. The firearm was designed to have all the rounds, even single ones, fed from the magazine.

Feeding the cartridge from the magazine incorporates the drag and deceleration produced by stripping and feeding the cartridge from the magazine. Hand chambering the round and allowing the bolt to fly into battery unhindered allows the bolt (and firing pin) to attain speeds that are significantly faster than is intended. This lends excess inertia to the firing pin, so it achieves primer impact with enough force to occasionally ignite one.

That's where the slamfires originate, and feeding from the magazine goes a long way toward preventing them.

Sometimes an M1 or M1A will double, firing a second round unintended. As long as the trigger group is essentially unmodified, this is not a slamfire or any other kind of mechanical malfunction.

It is an operator error. It is caused by babying the trigger. Again, the trigger is designed to be operated firmly and deliberately, pulling moderately quickly to the rear, all the way to the stop.

There exists a point along the path of the trigger where sear engagement is lost, but the trigger is not yet far enough to the rear to reengage the sear to the hammer hooks, entrapping it. The result is that the hammer rides the bolt, and will often fire again once the bolt has gone far enough into battery to allow the firing pin to clear the safety notch. The very presence of that safety notch is a tacit admission of the condition.

The design criteria is based upon having the operator pull the trigger firmly, smoothly, and without hesitation all the way back to the stop. Moving the trigger slowly rearward, 'hovering' near the release point, failing to follow through to a complete pull distance, will only aggravate the issue, and greatly increase the chances that doubling will occur.

I once experimented with deliberately inducing doubling. With a lot of (and I might add, nonproductive) practice, this condition can be induced with <span style="font-style: italic">some</span> repeatability. It serves no useful purpose, as the Garand, and M1A/M14 are all uncontrollable under conditions of full automatic fire. The additional round pretty near always goes somewhere around 5-10MOA high, depending on the shooter.

Greg
 

BeerAlchemist

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Jul 12, 2009
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Re: Slam fire and primers

Thanks guys...its amazing that I have shot 10k's of rounds out of handguns and 1k's through an AR but until I decided to reload and begin doing some long range shooting how much more information I need to acquire.