308AR Blowing Primers / Case Head Swipe?

[user]

Criterion Barrel with the M118LR Match Chamber. Mid Length Gas. SLP Adjustable Gas Block. Carbine extension with 308 Heavy Slash Buffer blowing primers with 165 Hornady and 168 Nosler factory ammo. From what I read this is not uncommon in 308ar pattern rifles. The gas is adjusted so it just cycles. And It still blows primers. Could it be time'in?

 

[NukeMMC]

Length of barrel? Suppressor? Any particular reason for the mid-length gas? Mine is rifle length and I have swipes when shooting suppressed. I have just upped the weight on my buffer from 8ozs to 10ozs.
I would suspect the gas impulse timing with the mid-length being a bit too soon and having too much dwell time. Talk to the builder and see what his experience says.

 

[fdkay]

have you considered a high pressure bolt?
Can't be retrofit to all systems.
https://ads.midwayusa.com/product/3...rts+(Not+Magazines)-_-JP+Enterprises-_-315790

 

[7mmFanBoy]

Start Reload probably going to be around 41g-42 powder. Factory going to have over 44g powder in it unless you go with cheaper ammo or lighter weight bullets

 

[user]

have you considered a high pressure bolt?
Can't be retrofit to all systems.
https://ads.midwayusa.com/product/3...rts+(Not+Magazines)-_-JP+Enterprises-_-315790

Thanks, will this help with blown primers?

 

[user]

Length of barrel? Suppressor? Any particular reason for the mid-length gas? Mine is rifle length and I have swipes when shooting suppressed. I have just upped the weight on my buffer from 8ozs to 10ozs.
I would suspect the gas impulse timing with the mid-length being a bit too soon and having too much dwell time. Talk to the builder and see what his experience says.

Thanks, its a 16" un-suppressed. Most 16" 308 come in middy's so thats what I ended up with. How have you upped your buffer weight to 10oz's? My Slash Heavy buffer is only 5.5.

Thanks

 

[NukeMMC]

Thanks, its a 16" un-suppressed. Most 16" 308 come in middy's so thats what I ended up with. How have you upped your buffer weight to 10oz's? My Slash Heavy buffer is only 5.5.

Thanks

That weight sounds like you are using a carbine-length buffer/tube. I am using a rifle-length buffer and tube. My rifle-length buffer has 6 weights inside it where a carbine has 3. I have replaced all 6 weights in my buffer with Tungsten weights. A normal steel weight is about 10.65oz, a Tungsten is 1.46ozs and an Aluminum is 0.15ozs. With a 308 rifle buffer housing/plug/pin & 6 rubber discs weighing about 1.5ozs (carbine is about 1.03 and AR15 rifle-length is 1.62) that puts my assembly at 10.3ozs. It sounds like yours is 3 Tungsten weights in an aluminum housing. If it is a stainless housing with internal weights, you can replace steel weights with Tungsten weights and up the weight 0.8ozs for each weight changed from steel to Tungsten.

 

[padom]

I have never had any of the dozen 308 semis Ive owned blow primers unless it was a load I loaded too hot... That M118LR chamber might be too tight, I would grab the golden standard Federal Gold Medal Match 168 and 175g and test that. See how that works for you. Also, a rifle length buffer tube with a JP AR10 SCS Gen2 will really reduce case head swipe.

 

[user]

Ok, I believe I found the problem. I found a previously undiscovered blown primer stuck in buffer retainer pin between the buffer and retaining pin. This primer kept teh buffer from pressing on the BCG when in battery. So, the bcg has a small amount of jump in it before contacting the bcg. Shot it today after discovering the issue and it shot ok with factor 150 and 168 gn ammo. Will shot it some more and see how it goes. But, no more blown primers today.!

 

[FLIGHT762]

I was going to ask you if you were shooting Hornady Superformance, it's been known to give gas guns fits.. Glad you found the issue. I have a first year production SR-25. Back in 1993, I was blowing primers with Federal GMM 168. I called Knight's and was told to keep shooting and the rifle would "settle in". It actually did. The chamber was really tight. Even today, after 2300+ rounds, the fired cases shoulders measure 1.631".

Back around 2006, I was shooting some Hornady 168 TAP ammo and was blowing primers in the SR-25 (SR-25 was a SWAT duty Rifle). I got ahold of Hornady L/E and sent some of the ammo lot back to them. They tested it, sent me some ammo from a re-adjusted lot and it worked fine after that. Gas guns can be very finicky. I also have a GAP 10 that puts the old SR-25 to shame.

You can get the most out of your gun by handloading for it.