AR10 firing pin issues

[jLorenzo]

I put together a mostly Aero gun with a BA barrel and Aero bolt, Aero upper/lower. Getting light primer strikes every once in awhile, 3-5 out of 100 and then after a couple hundred rounds 1 or 2 per 25 round mag.
I bought a cmmg firing pin (darker colored pin pictured) which is a touch longer but won't go all the way into the bolt because of the back end diameter of the firing pin hole in the bolt.

Wtf

 

[bfoosh006]

I can't quite tell... your first photo, is that a tapered FP ? ( Sure looks like one )

And can you measure the diameter of both FP's at the end of the longest shank, by the smaller collar ?

I can compare that measure measurement to what I have on hand .

Do you have a link to the specific BCG ? ( Aero uses 2 different styles )

And my rabbit hole of a thread.... https://www.snipershide.com/shooting/threads/308-6-5cm-fp-tip-sizes-and-the-variety-i-found.7222014/

 

[srt-4_uk]

When you get the light strike, are they extremely hard to extract?

 

[misser]

JP enterprise HP bolt

 

[jLorenzo]

When you get the light strike, are they extremely hard to extract?

Not that I remember but there may have been one or two. Fire upon second try every time.

 

[jLorenzo]

I can't quite tell... your first photo, is that a tapered FP ? ( Sure looks like one )

And can you measure the diameter of both FP's at the end of the longest shank, by the smaller collar ?

I can compare that measure measurement to what I have on hand .

Do you have a link to the specific BCG ? ( Aero uses 2 different styles )

And my rabbit hole of a thread.... https://www.snipershide.com/shooting/threads/308-6-5cm-fp-tip-sizes-and-the-variety-i-found.7222014/
View attachment 8480120

I will have to check/do that when I get home today. The first silver pin the the Aero one that came in their nitride bcg.

 

[jLorenzo]

Side note; I will not be ordering anymore AR10 barrels without a matched bolt.

 

[srt-4_uk]

Assuming you don't have a damaged firing pin, sound slike what's happening is the BCG isn't going back fully into battery. What seems like a light strike is a safety feature. It keeps the round from firing without the bolt being fully locked up. That's why it happens more with a dirty gun.
A longer firing pin isn't the answer. A stronger buffer spring, more lube, or different mags are your fix.

 

[db2000]

JP enterprise HP bolt

I thought I had an AR10 JP HP bolt and looked back at my order and turns out it was just an JP “Enhanced” AR10 bolt. Just an fyi
Definitely agree with matched bolt for sure.
AR10s are finicky to Frankenstein and most rec not doing that unless it’s a proven recipe

 

[jLorenzo]

Assuming you don't have a damaged firing pin, sound slike what's happening is the BCG isn't going back fully into battery. What seems like a light strike is a safety feature. It keeps the round from firing without the bolt being fully locked up. That's why it happens more with a dirty gun.
A longer firing pin isn't the answer. A stronger buffer spring, more lube, or different mags are your fix.

How would I know which buffer spring is stronger before ordering?

 

[jLorenzo]

Assuming you don't have a damaged firing pin, sound slike what's happening is the BCG isn't going back fully into battery. What seems like a light strike is a safety feature. It keeps the round from firing without the bolt being fully locked up. That's why it happens more with a dirty gun.
A longer firing pin isn't the answer. A stronger buffer spring, more lube, or different mags are your fix.

I am using pmags, happens with all of them. The bolt does seem a little stiff in the bcg but I have been keeping it clean and being liberal with the lube. Took awhile to get things smoothed out between all the moving upper parts. Very sandy/gritty feeling at first.

 

[jLorenzo]

Sounds exactly like the symptoms of a high pressure round?

Ftf with a light primer strike?

 

[918v]

Assuming you don't have a damaged firing pin, sound slike what's happening is the BCG isn't going back fully into battery. What seems like a light strike is a safety feature. It keeps the round from firing without the bolt being fully locked up. That's why it happens more with a dirty gun.
A longer firing pin isn't the answer. A stronger buffer spring, more lube, or different mags are your fix.

That’s what I was going to say. Also, check headspace and the ammo shoulder length.

 

[bfoosh006]

Side note; I will not be ordering anymore AR10 barrels without a matched bolt.

And a FP !!

BTW, What ammo is it ? Reloads ?
If reloads, Are the primers fully seated ? If not fully seated... the first FP strike may be seating them, and the second try fires it.

 

[srt-4_uk]

How would I know which buffer spring is stronger before ordering?

Companies like Wolff and Springco have different weight springs and are labeled.

Are you using reloads or factory ammo? The fact they fire second time around doesn't sound like a headspace issue, but it could be right on that edge.

 

[bfoosh006]

@jLorenzo


I think I may know "why" the CMMG FP won't seat all the way.

The Tapered FP's I have on hand , have a SD .068" tip size, ( both KAK and Azimuth , Aero ( in some of their BCG's ) and Craddock use these for sure as well as a few others ) and a shank size of .1525- .1540... most were of the 8 I checked were .1530".
So most likely just variance in the chrome thickness.
FWIW... the longest Tapered FP was 3.937", the shortest was 3.936"

The CMMG FP, like the one you bought, .074" Tip size. So it probably can't go through your Bolts FP hole. Shank size was a consistent .1525" for all 4 of them.
OAL, was also 3.938"... probably just a insignificant difference between yours and mine.


To find out if that is the "issue" ... try sticking the AERO FP tip in through the front side of the bolt face, vs the CMMG FP tip.

As to why you are getting soft primer hits... I am not 100% positive... but, as mentioned earlier, make sure primers are fully seated and maybe the round isn't 100% sized for your chamber , and maybe double check the hammer spring is installed correctly ( The correct side up )

 

[jLorenzo]

Companies like Wolff and Springco have different weight springs and are labeled.

Are you using reloads or factory ammo? The fact they fire second time around doesn't sound like a headspace issue, but it could be right on that edge.

Both. Federal brass, cci 200s, varget/ar comp, variety of bullets. Never had a single misfire ever of any ammo I've loaded. Federal GMM and blue box had the same issue.

 

[msgriff]

For the intermittent problem with the original bolt and FP, I'd be looking at the FCG.

 

[jLorenzo]

For the intermittent problem with the original bolt and FP, I'd be looking at the FCG.

Larue 2 stage, springs oriented correctly.