I recently built an AR10 in 6.5 Creedmoor , Luth AR upper , Aero Precision lower , Brownells BCG and a used Timney trigger , went on the range today with some hand loads and had several discharges on bolt release , the BCG appears to be all good , I`m guessing the trigger is at fault? I acquired the trigger from an old rifle , an AR15 , is this common with light triggers or very unusual ? I did bump test it when I built and all was good , 100 or so shots from new this problem arises . Your thoughts and experiences are appreciated.
AR10 6.5 Creedmoor fired on releasing bolt....
- Thread starter Rec1er
- Start date
Its not the type of primers. Ive been reloading and shooting AR's, both AR15's and AR10's for years and Ive never had a slam fire with 200, BR2, 205, 205M, 210, 210M.
Are your primers properly seated all the way down into the primer pocket with a slight crush? If you run your finger over the back of the case, is the primer slightly recessed?
Is your barrel properly headspaced to your bolt? Did you have it headspaced, or if not, did you check with with a Go/No-Go. Any time I build a large frame gasser I always have the bolt headspaced to the barrel and check with Go/No-Go. Large frame gassers are not the same as throwing an AR15 together.
Is your trigger firing when you get these slam fires? Meaning if your trigger is cocked, you have a slam fire, is it then in the fired position? Have you removed the trigger and checked if its still happening?
Are your primers properly seated all the way down into the primer pocket with a slight crush? If you run your finger over the back of the case, is the primer slightly recessed?
Is your barrel properly headspaced to your bolt? Did you have it headspaced, or if not, did you check with with a Go/No-Go. Any time I build a large frame gasser I always have the bolt headspaced to the barrel and check with Go/No-Go. Large frame gassers are not the same as throwing an AR15 together.
Is your trigger firing when you get these slam fires? Meaning if your trigger is cocked, you have a slam fire, is it then in the fired position? Have you removed the trigger and checked if its still happening?
It was head spaced , I`ll re check it , I may load some cases with just primers , no powder / bullet and see what happens , trigger out.
Is your hammer actually dropping when you release the bolt? May want to double check that your trigger is installed properly.
This is most bizarre. To me it looks like the rifle fired without the firing pin striking the primer (so no trigger malfunction). The pressure from the shot caused the primer to flow into the firing pin hole in the bolt face. This hole is unsupported because there is no extended firing pin to stop the material flow.
I can think of two possible issues:
1. The primers aren't seated deep enough into the primer pocket and therefore protrude past the base of the cartridge. The force of the bolt slamming against the primer is igniting them (but shouldn't)
2. There is a manufacturing defect with this batch of primers (unlikely)
I would definitely contact the primer manufacturer for their thoughts. Interesting mystery.
I may have answered my own question . I had just fitted a Luth AR AR-308 COMMERCIAL CARBINE BUFFER ASSEMBLY , the buffer spring is very aggressive and slams the BCG forward with a lot of energy , I never had this problem with my other full length buffer tube.
I dunno.... I would *hope* that primers are engineered with enough of a safety margin to not detonate because someone is using an out of spec gorilla-strength spring..... There is too much liability in this game for sloppy engineering.
Trigger is a drop in Timney so hard to fit wrong , no the hammer is not dropping when it slam fired.
Again....major design / engineering flaw with an amazing amount of liability, so highly unlikely.
FWIW my GAP10 does have a firing pin return spring to prevent just this. The AR10 firing pin has more mass. I'm not sure if this is standard across all AR10 rifles. I would disassemble the bolt carrier assembly to check this.
You may just want to spend the $2 to do this right
https://www.wolverinesupplies.com/productdetail/amlea1011_armalite-ar10-firing-pin-spring.....Or contact whoever manufactured this and have them correct it.In thinking about it some more, the primer extrusion into the bolt face you are seeing may be an indication of a slam fire since there is no hammer pressure on the back of the firing pin to retard the firing pin from being pressed back into the bolt assembly.
Root
Isn’t that a true Armalite firing pin from Armalite compatible BCG? My older AR10 308 GAP looks same. DPMS pattern are different.
Isn’t that a true Armalite firing pin from Armalite compatible BCG? My older AR10 308 GAP looks same. DPMS pattern are different.
Rec
Have you disassembled BCG and cleaned thoroughly to determine if any dirt or objects impeding movement of firing pin below bolt face?
Have you disassembled BCG and cleaned thoroughly to determine if any dirt or objects impeding movement of firing pin below bolt face?
Lol. So much speculation.
I've built 25+ Large frame gassers with Toolcraft, Rubber City and JP complete BCG's and everything from extra power/slash heavy buffers to Tungsten SCS and NONE have a spring on the firing pin and never once had a slam fire in 50k+ rounds....
You got something else wrong, out of spec part but you dont have too heavy a spring causing your rounds to go boom...
I'm gonna speculate and say out if spec bcg or improperly seated primers
I've built 25+ Large frame gassers with Toolcraft, Rubber City and JP complete BCG's and everything from extra power/slash heavy buffers to Tungsten SCS and NONE have a spring on the firing pin and never once had a slam fire in 50k+ rounds....
You got something else wrong, out of spec part but you dont have too heavy a spring causing your rounds to go boom...
I'm gonna speculate and say out if spec bcg or improperly seated primers
What barrel? You sent your bolt to that barrel maker and had it headspaced to your brownells bolt??
No way to tell if the hammer fell setting it off because obviously the carrier will reset the hammer. Unless you got some quick eyes.
You can drop the bolt without ammo and see if the hammer falls. That's about it.
After noticing this topic I'm going to speculate something. The hole in the primer is from over pressure. (don't ask how I know) the primer does not get flat because the hole vents the pressure.
I'm willing to bet the op has the flat disks in the bolt and they are getting stuck against the firing pin causing it to strike primers. Or the hole blew alot of debris and that is causing the fireing pin to remain forward enough.
Obviously the pin isn't stuck forward solid or the rifle would run away (fire automatically until empty)
I can only speculate along with everyone else at this point. If it is not a slam fire issue due to buffer and spring combination, is the firing pin sticking occasionally in the forward position? Seems like that would be hard to test for other than with primed cases. And if you can duplicate it this way, I would separate the halves to see where the hammer is.
If the hammer is coming forward, it sounds like the initial problem when PSA released their .308 lowers with certain Geissele triggers. But that would mean something out of spec in relation of upper to lower. I would think odds against this.
The only other thing that comes to mind is that the one Timney I own uses set screws to hold the pin in place. It would have to be fairly loose to have an issue and probably lose the pin I'd think.
I would bet more on an occasional high primer than a mechanical flaw. Have you reamed the primer pocket on this brass or can you measure the depth on a case with a blown primer vs. the others?
If the hammer is coming forward, it sounds like the initial problem when PSA released their .308 lowers with certain Geissele triggers. But that would mean something out of spec in relation of upper to lower. I would think odds against this.
The only other thing that comes to mind is that the one Timney I own uses set screws to hold the pin in place. It would have to be fairly loose to have an issue and probably lose the pin I'd think.
I would bet more on an occasional high primer than a mechanical flaw. Have you reamed the primer pocket on this brass or can you measure the depth on a case with a blown primer vs. the others?
Yep, if the rifle has pierced any primers completely strip the BCG and bolt head and look for little pieces of primer cups trapped anywhere. Also make sure the firing pin didn't get torched and sticks in the bolt.
When this happened on my GAP10 a piece of a pierced primer stuck the firing pin forward and the rifle ran away full auto for the rest of the magazine. Kind of exciting when you aren't expecting it...
This, you may have had a pierced primer "disc" kicking around in the FP channel on the bolt... or possibly in the Timney Trigger works.
And a PP disc( or even multibule ) can lodge against a FP causing an issue. Or down in the trigger works...
I bet it fell out without being noticed.
After a bit of thinking about it I decided to run some primed cases through (no powder , no bullet) I just released the bolt on all three of these and did not pull the trigger (the trigger did not fire on its own accord either ) You can clearly see on the pic that the firing pin is indenting the primers purely from inertia , these primers didnt fire and are still live so if I`d not fully seated a primer it would fire and maybe even with a fully seated primer , next step is to change the buffer spring and try some more primed cases .
Maybe Luth AR , the stock/buffer assem supplier should warn customers of a potential hazard ?
Maybe Luth AR , the stock/buffer assem supplier should warn customers of a potential hazard ?
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Dimpling of the primer is normal since the firing pin is floating. However the amount of dimpling you’re showing is significantly more than anything I’ve ever seen. Usually it’s just a tiny spot that’s hard to see.
Reducing spring weight and firing pin weight may help here.
Reducing spring weight and firing pin weight may help here.
Lennyo beat me to it. Dimpling of the primer is normal in a large frame gasser but they shouldnt be igniting..
Get yourself one of these.
Get yourself one of these.
Toolcraft AR10 308 Bolt Carrier Group Black Nitride
Toolcraft AR10 308 Bolt Carrier Group - DPMS compatible, forward assist serrations for use with 308 parent case calibers. Includes Toolcraft's hassle free lifetime warranty. Arm or Ally is the internet's largest dealer of Toolcraft Bolt Carrier Groups. Thousands in stock, ready to ship!
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Put them in the mag and let the bolt pick them up. You will quit having slam fires.
I've had a .223 AR slam fire on one of my reloads with a high primer. I had planned to ease the bolt down on the round which setting on top of the mag, but got in a hurry and let the bolt fly. The round detonated before it was fully seated in the chamber. When I got home, found my barrel had rotated and sheared the barrel extension pin. I was lucky.
I had a DPMS large frame AR that would double or slam fire. I found the firing pin retaining pin was bent. It would rotate so that it would press against the firing pin holding it in the forward position and the round would go off as soon as the bolt locked up. After replacing with a new straight retaining pin it was fine.
