Why am I piercing primers on this 6.5AR?

[Basic user]

Loaded up a new load for this 6.5cm AR, and right out of the gate started piercing primers. and primer flow on some. Gun only has approx 40 rnds on it, and no piercings on those. First 20 was some standard issue S&B 140s, which shot really well, then a few mild reloads (which I dont remember the specs off hand) which were fine as well.
These loads were alpha brass, federal srp's, berger 130s over 35.7gr of varget, (37.5 is berger book max) and 40.1gr of H4350 (berger book max is 41.6). Both beat the necks up pretty good (dented mouths, and scored necks, w/ mild ejector swipe & extractor marks)
The bolt and bolt carrier is Lantac's match model. Mcgowen custom barrel w/ superlative gas block (dont remember the setting) and a supressor on. 2582fps was the average on the 35.7 of varget, and 2554 was the average on the 36gr of varget.

 

[Rangemaster]

Check your shoulder bump. You might have too much bump which is a common problem with piercing the primer.

 

[LR1845]

I am not a gas gun guy but does you BCG have a large firing pin?

 

[hlee]

Best bet is you just need a high pressure bolt- they use a smaller diameter firing pin. Fairly common (read required) in 6.5 cm AR builds.

 

[Basic user]

Check your shoulder bump. You might have too much bump which is a common problem with piercing the primer.

I see. I will see if I can measure that.

 

[Basic user]

Best bet is you just need a high pressure bolt- they use a smaller diameter firing pin. Fairly common (read required) in 6.5 cm AR builds.

I read here that all that does is mask a problem instead of treating it. What do you think about that?

 

[Basic user]

I am not a gas gun guy but does you BCG have a large firing pin?

I feel it does; though, as compared to what?

 

[spife7980]

I read here that all that does is mask a problem instead of treating it. What do you think about that?

But the large firing pin is the issue, changing it out to a hp bolt with associated firing pin will lessen the distance the thin primer material must hold its self up to the pressure. The issue is your large pin bolt is too wide to support the small rifle primer pressure.
Or change to LRP brass and actually cure it.

Measure the firing pin, close to .060 is small, closer to .080 is large.

 

[Basic user]

But the large firing pin is the issue, changing it out to a hp bolt with associated firing pin will lessen the distance the thin primer material must hold its self up to the pressure. The issue is your large pin bolt is too wide to support the small rifle primer pressure.
Or change to LRP brass and actually cure it.

Measure the firing pin, close to .060 is small, closer to .080 is large.

I see. I'll measure when I get home.

 

[ShtrRdy]

Which primer model are you using? Federal primers generally have thinner/softer cup.

 

[Basic user]

Which primer model are you using? Federal primers generally have thinner/softer cup.

I think 205s.

 

[BobinNC]

Federal makes 3 types of Small Rifle Primers:

Champion Centerfire Primer, .205, Small Rifle 0.0225 cup thickness​

Gold Medal Centerfire Primer, .205, Small Rifle Match 0.0225 cup thickness​

Gold Medal AR Centerfire Primer, .205, Small Rifle AR Match 0.0255 cup thickness​

Cup thickness does make a difference. Which Fed primer your using might be the root of your problem.

 

[Basic user]

I see. I definitely use the standard issue champions. I should re-examine my firing pin tip, and protrusion length as well.

 

[FLIGHT762]

If you're using small primer brass, you will need to use a primer that has a thicker cup as BobinNC pointed out. Other thicker primer cup brands are CCI 450's, CCI BR 4, CCI 41, Remington 7-1/2 and the Federal Small Rifle AR match.

I would try a thicker primer cup before buying a High pressure bolt. The pin hole diameter on the H/P bolt is about .068". The standard bolt pin hole diameter is .070" or so. The H/P firing pin tip will be about .066".

There's a lot of info on the net about this, especially when using large frame AR's in 6.5 CM.

I think you Lantac match bolt is the larger pin size.

This was discovered a few years ago. Nearly all of the commercially made 6.5 CM AR's have the H/P bolt.

Did you put your AR together yourself, or did you buy a the Rifle from a commercial vendor?

Decades ago, David tubbs was using an SR-25 for L/R matches. Even in 308 Win., he was blanking L/R primers with the stout reloads he was using. He found that some of the firing pin holes in the standard bolts were over sized, causing the blanking.

His remedy was a bolt with a pin hole not to be over size. The second thing he had done was to move the gas port a couple of inches forward to drop port pressures. A Gunsmith, Scott Madesha was doing this conversion. Tubbs finally gave up on the SR-25 platform and moved on.

A H/P bolt should fix your issues along with thicker S/R primers.

Large frame AR's can't take top end pressures that Bolt guns can. Your brass can get beaten hard.

I've been shooting and reloading For a first run SR-25 since the mid 1990's. In 2013, I bought a GAP 10 308. I still have both guns. The GAP 10 shoots better than the SR-25.

 

[straightshooter1]

Loaded up a new load for this 6.5cm AR, and right out of the gate started piercing primers. and primer flow on some. Gun only has approx 40 rnds on it, and no piercings on those. First 20 was some standard issue S&B 140s, which shot really well, then a few mild reloads (which I dont remember the specs off hand) which were fine as well.
These loads were alpha brass, federal srp's, berger 130s over 35.7gr of varget, (37.5 is berger book max) and 40.1gr of H4350 (berger book max is 41.6). Both beat the necks up pretty good (dented mouths, and scored necks, w/ mild ejector swipe & extractor marks)
The bolt and bolt carrier is Lantac's match model. Mcgowen custom barrel w/ superlative gas block (dont remember the setting) and a supressor on. 2582fps was the average on the 35.7 of varget, and 2554 was the average on the 36gr of varget.

Alpha brass has a little larger flash hole than the standard SRP brass, which tends to produce pierced primers (something they've talked about on their website). I had the same issue with my .308 using Alpha brass and Rem 7.5's solved the problem. The cure, assuming nothing else is at issue, is to use primers that are thicker, like Remington 6.5's or 7.5's, CCI No 41's, BR4's or magnum primers. All these have thicker cups to resist piercing.

 

[Basic user]

If you're using small primer brass, you will need to use a primer that has a thicker cup as BobinNC pointed out. Other thicker primer cup brands are CCI 450's, CCI BR 4, Remington 7-1/2 and the Federal Small Rifle AR match.

I would try a thicker primer cup before buying a High pressure bolt. The pin hole diameter on the H/P bolt is about .068". The standard bolt pin hole diameter is .070" or so. The H/P firing pin tip will be about .066".

There's a lot of info on the net about this, especially when using large frame AR's in 6.5 CM.

I think you Lantac match bolt is the larger pin size.

Nearly all of the commercially made 6.5 CM AR's have the H/P bolt. This was discovered a few years ago.

Did you put your AR together yourself, or did you buy a the Rifle from a commercial vendor?

I assembled it myself. I think I have a box of remingtons, and cci mags. I will try that as well.

 

[FLIGHT762]

is to use primers that are thicker, like Remington 6.5's or 7.5's, CCI No 41's or magnum primers. All these have thicker cups to resist piercing.

Remington 6 1/2 primers do not have a thicker primer cup. It is .020" thick. Remington specifically warns not to use th e 6 1/2 in higher pressure cartridges like 17 Remington, 222, 223 etc. The 6 1/2 primer was designed to be used in lower pressure cartridges like the 22 Hornet & 218 Bee.

 

[straightshooter1]

Remington 6 1/2 primers do not have a thicker primer cup. It is .020" thick. Remington specifically warns not to use th e 6 1/2 in higher pressure cartridges like 17 Remington, 222, 223 etc. The 6 1/2 primer was designed to be used in lower pressure cartridges like the 22 Hornet & 218 Bee.

You're RIGHT! My BAD!

 

[FLIGHT762]

Not trying to bust your chops, just want to get info out the for the O/P.

 

[bfoosh006]

This might help , while measuring your FP tip size.

https://www.snipershide.com/shooting/threads/308-6-5cm-fp-tip-sizes-and-the-variety-i-found.7222014/

FWIW... your Lantac ENHANCED 308 BCG should be right around these specs..
Lantac "Enhanced complete 308 BCG".. single ejector, "forward facing gas ports" w/ Small Diameter FP Tip size and Bolt face hole.
NOTE... the The Lantac sold Bolt and FP I mentioned in the first post... DO NOT interchange parts, with this Bolt and FP tip size .... one or the other Bolts and FP's most be used with the other.
You can use the the other mentioned individual Lantac Bolt Spare parts, and FP , with the carrier. But the FP tip sizes matter.
As in ... the Larger tip sized FP won't work with the "Enhanced" bolt face small diameter hole.
Tapered SD FP tip size... ( 2x ) .067.... Bolt face FP hole... .070"

https://www.lantac-usa.com/product-page/enhanced-bcg-full-auto-style-308-7-62-nitrided

And it does sound like the primers are "thin", specially since you are firing suppressed.

What buffer weight are you using and what recoil spring.