AR 10 light primer strike

[jLorenzo]

I put a Aero upper and Ballistic advantage barrel together and am getting light primer strikes here and there. Put the heavy spring in the Larue 2 stage, still happens. Most rounds fire but every range trip out of 3 had a few light strikes. New CCI 200s with varget, no issues in other guns.

I have resized brass fired from the chamber and was not able to bump the shoulder with the die touching the shell holder. I also noticed a little bit of soot on the shoulders of some of the rounds. If I rechamber a round that failed to fire, they always fire on the second try. Headspace probably? Its an Aero M5 bcg. Ballistic advantage 18" hbar 308. I need a new bolt or a new barrel if thats the case right?

 

[bfoosh006]

First thing that came to mind, The primers are fully seated ?

 

[LRRPF52]

I put a Aero upper and Ballistic advantage barrel together and am getting light primer strikes here and there. Put the heavy spring in the Larue 2 stage, still happens. Most rounds fire but every range trip out of 3 had a few light strikes. New CCI 200s with varget, no issues in other guns.

I have resized brass fired from the chamber and was not able to bump the shoulder with the die touching the shell holder. I also noticed a little bit of soot on the shoulders of some of the rounds. If I rechamber a round that failed to fire, they always fire on the second try. Headspace probably? Its an Aero M5 bcg. Ballistic advantage 18" hbar 308. I need a new bolt or a new barrel if thats the case right?

What are your pre and post-firing shoulder datum measurements from case head to mid-shoulder?

Sounds like your shoulders might be getting moved too far back.

Do you have the Hornady headspace comparator?

 

[msgriff]

Is the hammer spring installed correctly? It's pre-installed in the tin, but you never know.

 

[jLorenzo]

What are your pre and post-firing shoulder datum measurements from case head to mid-shoulder?

Sounds like your shoulders might be getting moved too far back.

Do you have the Hornady headspace comparator?

I do. I had brass fired from a bolt gun so havim

What are your pre and post-firing shoulder datum measurements from case head to mid-shoulder?

Sounds like your shoulders might be getting moved too far back.

Do you have the Hornady headspace comparator?

I had brass fired in a bolt gun, didnt know the gas guns new chamber so I sized touching the shell holder to the die. After firing some brass through the new barrel I went to resize and could not get the should to move even with the shell holder touching the die. I'll have to resize some and measure again but the shoulders werent bumping back. Still 100+ rounds all chambered and fired. A handful of light primer strikes, all fired on the second try.

 

[jLorenzo]

First thing that came to mind, The primers are fully seated ?

Yes I have used these primers and brass in a bolt gun without issues. I seat primers on the press.

 

[Rangemaster]

Check your headspace vs fired and unfired brass first. For a semi AR rifle you should have a 5 thousands shoulder bump. Anything over that will give you light primer strikes. If you have a bump more than that try seating the bullet a little longer to see if that helps.

 

[jLorenzo]

Check your headspace vs fired and unfired brass first. For a semi AR rifle you should have a 5 thousands shoulder bump. Anything over that will give you light primer strikes. If you have a bump more than that try seating the bullet a little longer to see if that helps.

I am not able to bump the shoulder on fired brass even with the shell holder touching the die.

 

[Rangemaster]

I am not able to bump the shoulder on fired brass even with the shell holder touching the die.

Wow, that is a tight chamber. You might have to get redding comp shell holders or grind off 10 thousand off the sizing die.

 

[BCP]

I am not able to bump the shoulder on fired brass even with the shell holder touching the die.

Its supposed to touch the die lol, in fact cam over a little bit like touch + 1/8th of a turn down farther.

Have the light strike rounds been easy to extract? Or did you have to tug it a bit? They could be slightly oversize and it's not going all the way into battery. Or it could be firing pin protrusion.

 

[jLorenzo]

Its supposed to touch the die lol, in fact cam over a little bit like touch + 1/8th of a turn down farther.

Have the light strike rounds been easy to extract? Or did you have to tug it a bit? They could be slightly oversize and it's not going all the way into battery. Or it could be firing pin protrusion.

I may have had to tug a bit to get them to eject. If its being over sized why would the shoulder be in the same spot when comparing fired vs. Sized brass? I decap before measuring.

Speaking on the die, sizing for another caliber to bump the shoulder 2-3 thou the shell hold does not touch the bottom of the die.

 

[jLorenzo]

Maybe I need to use a small base die? I have one with a broker decapping pin. I think I could swap a new pin over to it. Both dies are RCBS.

 

[BCP]

Maybe I need to use a small base die? I have one with a broker decapping pin. I think I could swap a new pin over to it. Both dies are RCBS.

I use an RCBS small base die for everything 308. Screw it down until it hits the shell holder and then a little extra (I go by how it feels like 1/8th turn maybe). Then trim to 2.00 so it can grow for awhile. After 4-5 loads the necks start to split so I chuck them.

You could make up 5-10 dummy rounds with whatever brass and any cheap bullet (no powder/rpimer obviously) then load them in the mag and let the bolt go on them one at a time. They should be super easy to extract no yanking on the charging handle.

If I had to guess I'd say it's not fully chambering them and the light strike you see is the free floating firing pin bonking the primer. Which is GOOD because if it fires when not fully chambered you have a potentially fatal situation.

***taking it on faith that you checked headspace before putting it all together and firing it lol

 

[jLorenzo]

I use an RCBS small base die for everything 308. Screw it down until it hits the shell holder and then a little extra (I go by how it feels like 1/8th turn maybe). Then trim to 2.00 so it can grow for awhile. After 4-5 loads the necks start to split so I chuck them.

You could make up 5-10 dummy rounds with whatever brass and any cheap bullet (no powder/rpimer obviously) then load them in the mag and let the bolt go on them one at a time. They should be super easy to extract no yanking on the charging handle.

If I had to guess I'd say it's not fully chambering them and the light strike you see is the free floating firing pin bonking the primer. Which is GOOD because if it fires when not fully chambered you have a potentially fatal situation.

***taking it on faith that you checked headspace before putting it all together and firing it lol

The primer looks the same as if I had just chambered the round and ejected it.
Keep in mind 90% of the rounds fire and function fine.

 

[PappyM3]

As I asked in the AR10 picture thread when you brought up this issue:

Did you try a new firing pin? Check your firing pin protrusion.

 

[jLorenzo]

As I asked in the AR10 picture thread when you brought up this issue:

Did you try a new firing pin? Check your firing pin protrusion.

I have not as finding the actual length spec on a firing pin when buying doesn't seem to be possible so essentially I would have to keep buying them and hope for the best without knowing if the new pin is any longer than the one I have.

 

[BCP]

The primer looks the same as if I had just chambered the round and ejected it.
Keep in mind 90% of the rounds fire and function fine.

If that's how the "light strike" looks it's not a light strike, the round isn't chambering and the firing pin isn't going forward.

 

[jLorenzo]

If that's how the "light strike" looks it's not a light strike, the round isn't chambering and the firing pin isn't going forward.

So do you think its the case web keeping it from fully chambering?

 

[jLorenzo]

If that's how the "light strike" looks it's not a light strike, the round isn't chambering and the firing pin isn't going forward.

 

[PappyM3]

I have not as finding the actual length spec on a firing pin when buying doesn't seem to be possible so essentially I would have to keep buying them and hope for the best without knowing if the new pin is any longer than the one I have.

They wouldn’t be advertised as different lengths. It could just be that yours is at the short end of spec or just slightly outside of spec.

Here are a few of mine:

Unfired JP 308HP:
0.05”

~400 rounds JP 308HP:
0.047”

~25 rounds Faxon cheapo:
0.038”

The fired JP has had zero issues. Neither has the Faxon, but admittedly I haven’t shot it much at all.

Apparently, according to a rando on ARFCOM), they should be 0.044" - 0.060". But, AR10s don’t have the same TDP that AR15s do.

 

[BCP]

My 716i is .040 or thereabouts.

 

[jLorenzo]

They wouldn’t be advertised as different lengths. It could just be that yours is at the short end of spec or just slightly outside of spec.

Here are a few of mine:

Unfired JP 308HP:
0.05”

~400 rounds JP 308HP:
0.047”

~25 rounds Faxon cheapo:
0.038”

The fired JP has had zero issues. Neither has the Faxon, but admittedly I haven’t shot it much at all.

Apparently, according to a rando on ARFCOM), they should be 0.044" - 0.060". But, AR10s don’t have the same TDP that AR15s do.

JP says not to use their pin with anyone elses bolt. Ideally Id like to have a matched bolt and barrel down the road.

Is that measurement how much the pin protrudes from the bolt?

 

[PappyM3]

…

Is that measurement how much the pin protrudes from the bolt?

Yup. But I suppose it might be hard if you don’t have a depth gauge. I just bought a digital one off Amazon so I can check bolt dimensions when I get new ones.

And because AR10s are not all standardized, I’d stick with an aero firing pin.

Though, looking at their site, it’s crazy that you can’t buy a spare firing pin or even a spare bolt/firing pin set. What the hell, Aero?

 

[jLorenzo]

Say I didnt bump the shoulder enough and some of the rounds had a tiny bit of excessive headspace keeping the bolt from going all the way into battery, would this keep the firing pin from striking?

 

[bfoosh006]

JP says not to use their pin with anyone elses bolt. Ideally Id like to have a matched bolt and barrel down the road.

Is that measurement how much the pin protrudes from the bolt?

For what its worth.. the JP NON-HP 308 bolt and firing pins for it have a one off FP Tip size.

JP Enterprises 308 ( Non HP ) Firing pins tip sizes, for all 3 products linked... .0735... NON Tapered
https://jprifles.com/buy.php?item=JPBC-PINS-308
https://jprifles.com/buy.php?item=JPFP-308TI
https://jprifles.com/buy.php?item=JPFP-308

So those will fit.. ( I assume, since JP does pay attention to their parts ) the NON HP Enhanced JP bolts... IE...
https://jprifles.com/buy.php?item=JPEB-308
https://jprifles.com/buy.php?item=JPEB-308 S

 

[bfoosh006]

This thread has some "308" FP tip sizes towards the end of it.
There is ( IMHO ) quite a few different Tip sizes that don't necessarily interchange with various 308 sized bolts.

I would follow your train of thought, and make sure you can buy the bolt and FP together.

https://www.snipershide.com/shooting/threads/questions-re-ar-10’s-lr-308’s-bolts.7198842/

I had not thought about measuring FP Lengths... and I have no way of measuring tip protrusion.

PappyM3 , can you post a link to the one you bought ? ( I don't know why this posted in Bold )​

 

[Cascade Hemi]

Your cartridges aren't going into battery. Take a sharpie and draw wide lines down the cartridge, from the ogive to the case web. Run the cartridge into the chamber, with the charging handle, from on top of the magazine. Extract it. Post pictures of the cartridge looking at the stripes.

 

[PappyM3]

Say I didnt bump the shoulder enough and some of the rounds had a tiny bit of excessive headspace keeping the bolt from going all the way into battery, would this keep the firing pin from striking?

If the bolt locks into the barrel extension, the firing pin can strike, the lug sides are flat and not angled, so it should be a binary thing of whether it locks fully or not at all. If it does not lock, the firing pin cannot protrude.

Perhaps there is some machining error making it only rotate into a not-quite-complete lock. I haven’t heard of that, but suppose it’s possible if the lugs on either the bolt or barrel extension have a slight angle to them. If that were the case then I suppose the firing pin could potentially just barely though the primer. I’ve never seen that happen, but I suppose it’s possible.

 

[PappyM3]

This thread has some "308" FP tip sizes towards the end of it.
There is ( IMHO ) quite a few different Tip sizes that don't necessarily interchange with various 308 sized bolts.

I would follow your train of thought, and make sure you can buy the bolt and FP together.

https://www.snipershide.com/shooting/threads/questions-re-ar-10’s-lr-308’s-bolts.7198842/

I had not thought about measuring FP Lengths... and I have no way of measuring tip protrusion.

PappyM3 , can you post a link to the one you bought ? ( I don't know why this posted in Bold )​

For a depth gauge?

I have this one: https://www.amazon.com/iGaging-400-D69-Electronic-Resolution-2-Position/dp/B00PFC490A/