Back to back slam fires today..would like opinions

[tscoz]

Took my Aero Precision LR308 to the range today for some load development using a modified Satterlee method. It's Aero upper, lower and bolt with over 500 rounds through it and up until today not a single malfunction.

I was two-thirds of the way through 30 rounds when I had my first ever slam fire followed by a second one. I also load for an M1 Garand, M1 Carbine, M1A and various AR15's so I'm familiar with the usual causes and my handloading procedures are such that I do everything I can to avoid them. I've never experienced one before today. Also, my shooting fundamentals are pretty decent so my usual shot follow through kept it from being a dangerous situation and I wasn't startled by it but I was definitely surprised.

I prime cases on my Redding T-7 because the arthritis in my hands is so bad that I don't have the strength to manipulate a hand primer but I check each primed case by running the edge of a plastic business card over the primer to be sure they're seated below flush as well as feeling each one with my thumb. I also use CCI34 mil-spec primers in this rifle so I'm almost positive that primer seating wasn't the cause. I went on to finish my last ten shots by loading and firing one round at a time in each magazine.

There are a couple of things that may be the keys to figuring this out. First, when I was loading these rounds, there were a couple where the primer seated much too easily. I was in a hurry to get them loaded so I continued on thinking I would fire them one more time and then cull them. Next clue is when thinking back, I seem to remember thinking that the second stage of the trigger pull seemed heavier than usual on those two shots. I have a LaRue MBT-2S flat trigger and each stage should have a 2 lb pull. I checked when I got home and the total trigger pull at that time was 4 lbs which is exactly what it felt like. Lastly, when I dropped the mag after the slam fires, an empty primer cup and a primer anvil fell out through the mag well. When I looked at the fired brass, one case had a missing primer. These weren't hot loads and none of the cases showed any evidence of over pressure.

I'm not all that knowledgeable about triggers but I do know that a blown out primer can get caught up in the trigger mechanism and cause a stoppage. Can it also interfere with the trigger to where it interferes with the functioning of the sear thus causing a slam fire (or double fire)? I haven't had a chance yet to inspect the rifle and trigger since I got home but I wanted to throw this out for your opinions before doing so.

Thanks in advance for any thoughts and replies.

 

[ShtrRdy]

How do you ensure that you don't cause a double-fire from your contact with the trigger?

 

[tscoz]

That’s something that I hadn’t thought of because I’ve never experienced it but today, in an effort to take myself out of the equation as much as possible, I kept a light touch on the trigger and with my shooting hand in general. I usually keep the trigger depressed until after my follow through but I’m not sure whether I was doing that today.

 

[Powder_Burns]

Its possible the anvil or something related interferred with the sear/disconnect, your comment on having a heavier than normal trigger press seems to reinforce that theory. I haven’t disassembled a 308 bcg yet but I thought the 308 firing pin has a spring to prevent intertia driven primer strikes.

 

[tscoz]

The 308 firing pin is free float, at least on my AP bolt it is.

 

[Powder_Burns]

The 308 firing pin is free float, at least on my AP bolt it is.

Guess I should take my bcg apart. lol

 

[Woollymonster]

I would have suggested a primer problem but you are using the right primers for semi auto. Before I knew better, I loaded up a batch with match primers. Got a lot of slam fires with those thin cups.

Maybe CCI threw a bad batch of primers? I would try a new lot. Also, I have never gotten slam fires with Winchester primers. Might try those.

You might also try the RCBS Bench Priming Tool. Easy on the hands, fast, and very accurate.

RCBS Bench Primer

 

[ShtrRdy]

That’s something that I hadn’t thought of because I’ve never experienced it but today, in an effort to take myself out of the equation as much as possible, I kept a light touch on the trigger and with my shooting hand in general. I usually keep the trigger depressed until after my follow through but I’m not sure whether I was doing that today.

Whenever I've tried to do that, (with an AR-15), I've had a double-fire happen. It's the same principal as 'bump firing' a semi-auto firrearm.

 

[smoothy8500]

A few things to consider:

I kept a light touch on the trigger and with my shooting hand in general.

thinking that the second stage of the trigger pull seemed heavier than usual on those two shots.

an empty primer cup and a primer anvil fell out through the mag well

The 308 firing pin is free float

Could have been either the light trigger hold/lack of follow-through, something blocking trigger disconnect, or dirty/protruding firing pin. Sounds like the primers were properly seated, but there was that loose primer pocket you mentioned.

 

[bghartm]

My guess is the loose primer pocket had something to do with it. Does the bottom of the case show any ejector and extractor marks?

 

[whatsupdoc]

OP when you say slam fire do you mean you press the bolt carrier release and the rifle fires when the bolt carrier slams shut without you touching the trigger or you are pulling the trigger and you get a double fire.

 

[Brisket]

If you're getting double fires - pulling the trigger fires the rifle and then on bolt close the rifle fires again - you might look at your trigger. I don't know anything about the larue, but my early model elftmann trigger disconnect wore down to the point it wouldn't capture the hammer on a regular basis

 

[mpk1996]

i bet shooter problem, not reloading problem.

most of the time when you get a problem like this its because you have a light trigger with a short reset (which is all good) and the recoil and your "light trigger finger" as you described, allows the rifle itself to move, reset the trigger and then as it settles back down fire again due to your finger pressure. I had it happen a couple of times on an AR15 that i was shooting off a bench with light shoulder pressure.

i would suggest to eliminate this possibility, do the opposite of what you are doing. use a lot of trigger pressure and just jerk it back and hold it, while really pulling the rifle back into your shoulder. squeeze everything tight and hold so the rifle moves as little as possible during recoil. you don't care about accuracy at this point, just trying to eliminate the issue. if you can shoot a ton of round without issue, go back to shooting the way you were. if you get a double fire, then you know its you and not your components

 

[Billl223]

Several years go I had slam fires with my JP .223. They suggested that I try a titanium firing pin. It worked and I still use it.

 

[FLIGHT762]

i bet shooter problem, not reloading problem.

most of the time when you get a problem like this its because you have a light trigger with a short reset (which is all good) and the recoil and your "light trigger finger" as you described, allows the rifle itself to move, reset the trigger and then as it settles back down fire again due to your finger pressure. I had it happen a couple of times on an AR15 that i was shooting off a bench with light shoulder pressure.

Probably ^^^^ this ^^^^. I've had this happen and it was with light pressure on the trigger. Try holding the trigger and let it go after firing, doing a slow trigger reset. You probably just bump fired.

 

[WildBill3/75]

If it is a true slam firing

Pierced primers can lengthen the firing pin from molten hot gas flowing through the bcg. Pull your firing pin and inspect. If this is the case you will see a ring a little behind the nipple area.

Your buffer could be to heavy.
Your spring could be to heavy.

You could be "double tapping" and not know it.

 

[tscoz]

I've thought about this a lot since yesterday and I'm pretty sure that I double tapped (bump fired) without realizing it. I went into the session thinking that I wanted to shoot the best groups possible and I was going to take myself out of it as much as possible. Honestly, I think the only contact that my firing hand had with the rifle was the pad of my trigger finger. I also didn't pull the stock into my shoulder much if any.

I've been shooting a long time and I'm embarrassed that I did this and even more so that it didn't occur to me that I did it. Thanks a lot guys. I figured that I could count on all of you. I'll try to get out to the range this week and go back to my usual technique. I'll report back and let you know how it went.

 

[smoothy8500]

Honestly, I think the only contact that my firing hand had with the rifle was the pad of my trigger finger. I also didn't pull the stock into my shoulder much if any.

Yeah, it happens. It's pretty common also with Garand and M14 shooters if they try to treat it like a bolt gun on the bench.

 

[ajwcotton]

It you lose a primer on a gas gun it is common to have a piece of the primer either jam the trigger keeping it from catching the hammer or a small piece stick to the firing pin and jamming it forward or sticking to the tip and making it longer. It may well be you bump firing it which is also quite common especially on large frame guns with light or short triggers. Either way check the trigger and bolt for firing pin debris and drive that gun like it was meant to be shot.