AR10 with 6.5 Upper showing signs of overpressure

[kenny1773]

Hello All

Having some concerns about signs of over pressure with my AR10 6.5 upper

This AR10 was a factory build Aero Precision in 308 with a 16" barrell

I then built up an Aero upper with a Ballistics Advantage 22" ultra match barrel and Aero BCG in 6.5 CM

I do not reload (just have not gotten there yet) so I am using all off the shelf ammo

Hornady ELD match 140 gr seems to shoot the best in this gun, but I tried a box of Sellier & Bellot 140gr and actually had primers blowing out of the back of the brass case and flying everywhere.

The gun has a fixed gas block, but I did put in an Armaspec AR-10 Stealth Recoil Spring and that seemed to help, but it is still doing it.

 

[Jolliec]

Hi-

I have the same barrel (but 24") on an Aero M5 lower with an Aero HP BCG (6.5CM).

Do you have a High Pressure Bolt? I believe there were issues with some of the original bolts w/6.5 CM.

 

[kenny1773]

I *think* I have a high pressure bolt, is there a way I can look at the bolt and tell?

 

[Bluewater132]

That ammo is to hot for your setup. You could be over gassed and not have enough dwell time and an adjustable gas block could help. Try other ammo and check the brass.

 

[Precision Underground]

Yea those with blown primers have a huge ejector print on them. Something is off there. I def would not run that ammo again and would be very cautious with others until you are sure that ammo was the issue.

 

[DavidAR10]

Get one of these:

The S&B may have had the shoulder pushed too far back
and/or
Your chamber may have been cut to max. spec or too long.

 

[Jolliec]

I have the Superlative Arms Adjustable Gas Block on mine. I was having issues with ejection/stovepipes prior to that.
Also would suggest checking headspace if you have access to gauges.

 

[VegasHKShooter]

Same here with the Superlative Arms Gas Block. I put that on mine when I installed the barrel. Not a single issue shooting suppressed or unsuppressed. I most definitely think the AGB is a necessity for the 6.5CM. So far, mine shoots sub MOA with the 140 ELD-M, BUT loves the 143 ELD-X. It’s closer to .6-.7 moa with the 143.

I don’t feed it the 143 AS MUCH, because my 3 other 6.5’s love the 140’s, so I tend to keep many more of those on hand.

 

[DRAM40A1]

As others have stated, you need an adjustable gas block on the 6.5 Creedmoor. Along with a high pressure bolt and likely a heavier buffer. BTW, what buffer system are you using?

 

[__JR__]

S&B, that tubby little round. It's going to running not far off the lands in a SAAMI 6.5CM throat which will drive the pressures up. Hot in most gas guns.

 

[Darqusoull13]

Hello All

Having some concerns about signs of over pressure with my AR10 6.5 upper

This AR10 was a factory build Aero Precision in 308 with a 16" barrell

I then built up an Aero upper with a Ballistics Advantage 22" ultra match barrel and Aero BCG in 6.5 CM

I do not reload (just have not gotten there yet) so I am using all off the shelf ammo

Hornady ELD match 140 gr seems to shoot the best in this gun, but I tried a box of Sellier & Bellot 140gr and actually had primers blowing out of the back of the brass case and flying everywhere.

The gun has a fixed gas block, but I did put in an Armaspec AR-10 Stealth Recoil Spring and that seemed to help, but it is still doing it.

Did you check headspace on that bolt?

The BA barrel is rifle gas? If so that port length is too short for 6.5.

Like others have said get an adjustable gas block. You can also run a JP heavy 308 silent captured spring. Those will drop the pressure and help keep the bolt locked a bit longer so you aren't trashing brass.

 

[__JR__]

I've been watching real close CBTO on factory 6.5CM (in my job description). S&B is the furthest out by far, and is loaded hot. If you're running anything less than SAAMI, you're probably loaded into the lands.

 

[kenny1773]

Thanks for all the replies!! Some great info here

I have an Armspec 308 spring - SRS-308 5.7oz. - this considered a heavy I beleive
The BA 22" barrel is a rifle gas system

I can shoot Hornady ELD 140gr match ammo and I do not have this problem. I really wanted a less expensive option. The first box of S&B I tried was fine, and it grouped fairly well, but the next box I tried did this.
Maybe S&B has a quality control issue?

From what I am reading I need to do the following

1. check head space - I wanted to buy some gauges anyway so will do that

2 buy and install an adjustable gas block

or option 3 just avoid S&B ammo in this gun

I contacted Aero, I do have a high pressure Aero bolt, so that should not be the issue.

 

[__JR__]

Kenny, just saying S&B is a bit hot and a bit close to lands for a gas gun. Not that I know anything more than the next guy, but am barreling 6.5's for KAC. FWIW.

 

[Fishin6061]

S&B is known to be a little on the hot side. Most has guns are over gassed right out of the gate. 6.5 has a narrow gas profile in the operating range compared to say a.260rem. Might think about an adjustable gas block like the SLR as well as rethinking your ammo.

 

[kenny1773]

I have a superlative arms adjustable gas block and some 6.5 go no go gauges on the way, will hopefully have some answers soon

and I understand what you are saying about S&B 6.5 ammo, I have a bolt gun I can shoot it in if I need to

 

[kenny1773]

Alright, I got the go - no go - gauges and it looks like I pass
bolt locks on go
will not lock on no go

I have the superlative gas block installed, and it's ready to be dialed in
Hoping to get out to the range today about noonish local time
wish me luck

My plan is to set the gas block to lock open on the lightest rounds I shoot (winchester 125 grain) and then see what happens on the others

I like the superlative detent clicks, if I need to I could dial back a little for the S&Bs

 

[Wile_Coyote]

My 6mm was doing the same thing. It had a Toolcraft BCG. Get an HP bolt. I just put one from JP in mine and that all disappeared.

I went through the same thing. Headspace suggestions, adjusting the SLR GB, buffer weights and springs... the bolt worked.

 

[Howland]

I've got a Gen II PA10 that leaves a pretty distinct ejector swipe with very modest charges from the manual but no blown primers. It doesn't help that I'm trying to find a good 180gr. load. One brand even gets the rim ripped right off.

I'm going to diagnose it as overgassed right now. I'll add an adjustable gas block before trying any more load workups. And if I'm doing that I'll throw a free float rail on it, and perhaps try a faster powder.

Most commercial ~155gr. ammo works just fine except the CBC and anything I try in 180gr.

 

[Wile_Coyote]

My 6.5 Creedmoor has an SLR adjustable gas block and JP SCS buffer in an H2 setup and an Aero BCG. No blown or pierced primers. Most commonly used load is a 147 ELD with a mid table charge of H4350 that makes good groups. The brass isn't beat and lasts through multiple loadings. Max table powder charges didn't tighten anything up.

Shooting with or without the supressor doesn't require any GB adjustment.

Only run a couple boxes of SB ammo, but didn't care for it and won't use it again.

 

[Spblademaker]

I've got a Gen II PA10 that leaves a pretty distinct ejector swipe with very modest charges from the manual but no blown primers. It doesn't help that I'm trying to find a good 180gr. load. One brand even gets the rim ripped right off.

I'm going to diagnose it as overgassed right now. I'll add an adjustable gas block before trying any more load workups. And if I'm doing that I'll throw a free float rail on it, and perhaps try a faster powder.

Most commercial ~155gr. ammo works just fine except the CBC and anything I try in 180gr.

Here’s a good example of an overgassed 6.5CM semi.

 

[JFR]

WTF? I don't even know what to say about those photos.

JFR

 

[JFR]

I will say, dump the S&B.

JFR

 

[Wile_Coyote]

That's ugly... never seen anything like that with mine

 

[Spblademaker]

WTF? I don't even know what to say about those photos.

JFR

That was my 6.5CM set with the adjustable block fully open, a +2 gas system, full weight BCG, Tubb spring and H1 buffer. 140 eld over 41.8 H4350 loaded 2.231 BTO. BCG would come back so fast, the spent case would do a 180 in the upper and get smashed by the BCG. Made block adjustments and the brass looks unscathed and ejects at 3-4 o’clock. That’s what I call overgassed. ?

 

[JFR]

Aaahhh... That explains it!

JFR

 

[Howland]

View attachment 7107872View attachment 7107871

Here’s a good example of an overgassed 6.5CM semi.

That'll buff out.



Just out of curiosity, did your overgassed situation leave ejector shine that stopped when you restricted the gas?

 

[kenny1773]

I guess S&B isn't going to work in my gun. I got everything dialed in for the lightest loads I shoot, the Winchester 120gr
I shot a box of the Winchester and it worked perfectly
I shot about 10 Hornady ELD 140s and they worked perfectly

I shot 3 S&B 140s and stopped as the 3rd one blew the primer completely out of the case
(the first two showed some rough ejector marks)

This is so strange as I shot 2 boxes of S&B in this same gun and didn't have any issues at all. I really think now there is something wrong with the S&B ammo I bought in the second round (these new ones are a different lot number)

Anyway, the first two boxes of S&B I had actually grouped well at 600 yards. I guess I need to give up on it at this point. If I want a cheaper ammo to shoot at 100 yards I will stick with the winchester

 

[Dustysa4]

That's actually a feature. It takes care of the decapping step for you. ?

At this point it's pretty safe to assume it's that lot of ammo. Just out of curiosity, did you run any or all of these over a chrono? I'd also be curious to know if they're chambering in the lands. Could be an overcharged lot, or maybe they didn't seat the bullet back far enough. Either condition can cause increased pressure. But it's moot at this point, just kind of interesting...

 

[Spblademaker]

That'll buff out.



Just out of curiosity, did your overgassed situation leave ejector shine that stopped when you restricted the gas?

There is a mark where the ejector pushed the case off the bolt face. Not to be confused with the mark left when the case head pushed into the ejector hole during an over pressure situation.

 

[kenny1773]

I just sent an email to Sellier & Bellot US Customer service. I am curious what they have to say

I included the lot # 6.5 Creedmoor 140 Gr FMJ BT LOT 28/89

This lot of ammo came from Sportmans Guide
The previous couple of boxes I bought early this year came from Outdoor Limited, but I have nothing remaining with the lot # on them.

 

[Spblademaker]

I guess S&B isn't going to work in my gun. I got everything dialed in for the lightest loads I shoot, the Winchester 120gr
I shot a box of the Winchester and it worked perfectly
I shot about 10 Hornady ELD 140s and they worked perfectly

I shot 3 S&B 140s and stopped as the 3rd one blew the primer completely out of the case
(the first two showed some rough ejector marks)

This is so strange as I shot 2 boxes of S&B in this same gun and didn't have any issues at all. I really think now there is something wrong with the S&B ammo I bought in the second round (these new ones are a different lot number)

Anyway, the first two boxes of S&B I had actually grouped well at 600 yards. I guess I need to give up on it at this point. If I want a cheaper ammo to shoot at 100 yards I will stick with the winchester

I had pressure issues with them in my bolt gun. Too hot as well. So I pulled the shit 140s out of them and pressed in SMK 120s.

 

[kenny1773]

I did not get any Chrono info from the ammo, but I should, the boxes that I had previously that worked well chronoed about 2600 fps in this gun, not too far off the Hornady ELD 140s

I might be tempted to shoot a couple more rounds and see

I also did not try any shots with the gas turned off, I completely forgot Had my wife with me at the range and I was distracted a bit

 

[kenny1773]

S&B replied right away
They stated that they have received no complaints about the lot number I have
They wanted pictures and details
They said based on the pictures they may want me to mail in (at their cost) the other 8 boxes of ammo I have for testing.

This sounds promising

I also sent them a picture of the Hornady and Winchester brass from the same gun so they can compare. I am sure they think it is my gun, but it would be to their advantage to make sure this ammo shoots in an AR10. At it's price point I am sure auto owners are the #1 target

 

[kenny1773]

some back and forth with S&B on this issue, going to agree it is just my gun that does not like this ammo. Shoots fine in their guns, so I will stick to Hornady match in my ar10, it seems to love this ammo, just unfortunate for me the price difference

S&B made good on an ammo exchange for a different caliber, and I am still a very happy customer just will not be shooting their 6.5 in my AR10

 

[__JR__]

some back and forth with S&B on this issue, going to agree it is just my gun that does not like this ammo. Shoots fine in their guns, so I will stick to Hornady match in my ar10, it seems to love this ammo, just unfortunate for me the price difference

S&B made good on an ammo exchange for a different caliber, and I am still a very happy customer just will not be shooting their 6.5 in my AR10

Depends on the throat. If I throated a gun specifically for 140 AMAX, S&B would not workie..

JR

 

[VegasHKShooter]

If your gun likes the Hornady ammo, I have had great luck with the American Gunner from them. It uses a 140 BTHP and still shoots great for the price. I buy it by the 200 round box. I have had super good luck with it and it is much better than the S&B ammo. The American Gunner clocks 2772 out of my 26” Bartlein on my A.I.
FWIW, this particular barrel is very fast. I’m getting 2800 out of my Hornady 140 ELD-M factory loads. So YMMV. But, it saves a decent bit of $$ for just plinking ammo.

 

[kenny1773]

Thanks for the suggestion, I did try AG and got horrible groups with it. Funny enough the 2 boxes of S&B I had that shot well grouped better than AG by a long shot. or Maybe I just got a little better at shooting this gun, I might give AG one more chance.

I found the Hornady Black that Academy sells also groups very well, Still $1 per shot, but saves some money over the ELD.

 

[kenny1773]

The barrel is a Ballistics Advantage premium ultra match fluted 22", no idea what it is throated for