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Posted: 11/24/2025 11:43:08 AM EDT
[Last Edit: Bearcat24][Edited]
| Have had this 12.5 inch 308 for a good 6 years. Put a AR Gold trigger in it. Sat in the safe for over a year. Brought it back out this year. Started slam firing. Replaced the trigger with the original trigger. Still doing it. Is it the spring thats weak that locks the bolt back or something else? Even when I lock the bolt back, the slightest bump will let loose the BCG. Am assuming its the spring but thought I would post this in case I am missing something. Its a Aero lower and a KAK upper. Appreciate your replies. |
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You might have excessive firing pin protrusion. There is a specification for the AR-15 but I don’t know the specification for the AR-10. The AR-15 minimum firing pin protrusion is .028” to maximum .036” or a tolerance .008”. Since changing the FCG didn’t stop the slam fire I’d definitely check the firing pin protrusion. You could test with an empty primed case. You can get a rough estimate of firing pin protrusion using a set of calipers. You might find the FP protrusion spec online or you might call Brownell’s technical support as they might be able to advise the specification. I found an old AR-15.com thread discussing AR-10 7.62x51 FP protrusion. “ AR15 5.56 firing pin protrusion = 0.028" - 0.036" AR10 308 firing pin protrusion = 0.044" - 0.060" (0.055" - 0.060" preferred)” I can’t verify this information is correct but I’d use this as a guide. |
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Since you have used two different triggers, are you shooting handloads?
If so, do you shoot these cases between different rifles and chambers? Cases fired in a fat chamber aren't necessarily getting sized enough if the rifle having slam-fires has a tight chamber. |
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Originally Posted By Bearcat24: I can bring back the BCG in lock position. Not inserting the magazine, give it a bump. BCG goes forward. Don't see how the firing pin would have anything to do with this. I use these reloads in other AR10's without issue. Almost every AR does this. Unless I'm not understanding, that's not a slam fire. A slam fire actually detonates the cartridge, not just sending the bcg home. |
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Originally Posted By Bearcat24: I can bring back the BCG in lock position. Not inserting the magazine, give it a bump. BCG goes forward. Don't see how the firing pin would have anything to do with this. I use these reloads in other AR10's without issue. All you have to do is remove the forward pressure of the BCG against the bolt catch for an instant and the bolt catch will snap down causing the BCG to return to battery. 100% normal. |
| Sorry for the misleading head line. I changed it. The BCG will not stay back locked when a tiny little bump. Thanks for the corrections folks. Just got back from the range with it. Finally got it sighted in with my sandman Nomad L. Plan on taking it apart and see if that lock mechanism is wore out and check other components. Appreciate the replies. |
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Sorry I thought OP had two different issues. Issue one being the bolt carrier is not holding on the bolt catch after a slight bump. When bolt carrier unintentionally is released the chambered cartridge ignites from the bolt slamming into battery. Sounds like the Bolt catch activation or movement issue like previously mentioned which is not near as serious an issue as an actual slam fire where a cartridge is set off. I’ve seen tolerance stacking where the bolt catch was tight inside the receiver and would not freely actuate. This happened to my Brother’s build with an AR-15 on a weekend with no extra bolt catch. We filed down the offending bolt catch to fit the receiver slot and put some cold blue on the slide catch after fitting. |
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Originally Posted By HighpowerRifleBrony: https://i.postimg.cc/BjPh7fBq/IMG_3222.jpg Not much holding it back. Was that from an empty mag or engaged manually? Manually engaged. Plan on replacing the latch and spring for starters. I have another on in my parts bin that looks exactly like the one installed. I was watching some videos today in reference the bcg not holding back. One showed 2 lugs locking onto the latch after he fixed his as mine shows one against the latch. We post back my findings. |
Just tried a different latch. Not sure but think its for the AR15 platform. Tried it anyways. Was worst. Sent off emails to Aero Precision about this latch since its their lower. Also sent a email to KAK industries since its their duel ejector BCG. Don't recall having this issue when I had a standard LR308 BCG in it. " /> " />
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Think I figured out most of this issue. If you look at the picture with 2 latches, the one I tried did push in all the way when I engaged the latch, but wasn't large enough to do the job, hence its probably for the AR15 platform. Went back just a bit ago and was looking at the latch. It would not push in that far that stopped it from raising the latch high enough to cover more lugs. Broke out the dremel and grinded down the inner part to create more travel. Look how much is actually covering the lugs. It does not close when bumped lightly or even a medium bump. Did give it a good wack and it did close the BCG. Think thats almost normal but not entirely sure. " />
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Looks like you solved the mystery> BTW, what lube do you use a year ago ? FWIW... FireClean ( when it was popular ) would "dry out" so bad , it would cause my BCG's to lock into the bolt lugs. A good whack would break them loose... but lesson learned. |
*Hold on to your AR-15s. Their magic must be very powerful, or they wouldn’t want them.*
JAFOM.... Just another fat old man.
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TOGC,IADC
JAFOM.... Just another fat old man.
________________________________
TOGC,IADC
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