LR308 case marks after firing?

[joshb]

You should see what an HK does to brass! It’s unusable after it’s fired.

 

[Rsadams]

Are you sure the headspace is correct...? And really 4:00 to 4:30 would be ideal as far as ejection in a carbine length gas system... If you're getting over pressure signs with factory ammo there's definitely a problem... Those primers don't look flat to me...

 

[Normandinpatriot]

Are you sure the headspace is correct...?

It is with in spec.... Both go and no go gauges closed up but the field gauge did not... I have contacted the barrel manufacturer and they assured me it should be safe to shoot with all factory loaded ammo(7.62x51 and 308)...

 

[Rsadams]

It is with in spec.... Both go and no go gauges closed up but the field gauge did not... I have contacted the barrel manufacturer and they assured me it should be safe to shoot with all factory loaded ammo(7.62x51 and 308)...

It almost looks like the firing pin hole is on the large side and the primers are flowing back into it...Am I just confused here but shouldn't it not close with the no go Gage in it... Sorry it's been a long day... I think you may have found your problem...

 

[Normandinpatriot]

It almost looks like the firing pin hole is on the large side and the primers are flowing back into it...Am I just confused here but shouldn't it not close with the no go Gage in it... Sorry it's been a long day... I think you may have found your problem...

308/ 7.62x51 has the three gauges because of the military application... as long as it doesnt close on the field gauge it should be good to go. May not give the accuracy, but will be safe... I gave this info to Ballistic Precision and they said it should be fine." All of our barrels are test fired and checked for headspace at the factory".. I asked about how different bolts would affect headspace and they were adamant it should be good with any quality bolt. Lantac has a great reputation and BP will take the barrel back if it doesnt shoot less than 1MOA... at the end of the barrel break in I shot 2 groups, 3 rds 1/2iin at 100yds with 175gn Sig Elite Performance OTM. and no signs of over pressure... it was 20 degrees hotter than when I shot this weekend....

 

[mac86951]

You have provided a bunch of good info. However you have not really answered the question i think i asked. Perhaps i asked poorly? I am not concerned on saving the brass. I understand why the brass is "beat up". I am not sure why with M118LR (175gr) and Lapua 308(168gn) ammo, both listing MV 2600 or less, I am getting signs of over pressure... Flattened/ popped/ bulged primers, ejector dents on the base. I understand the extractor marks are likely caused by a sharp extractor with an overly strong extractor spring.

I am using a Ballistic Advantage 1:10 18" barrel, Lantac Enhanced BCG, standard LR308 carbine buffer and spring in a VSeven Stainless Steel 7 position buffer tube. I believe the tube is slightly longer than a standard carbine buffer tube at 7.25". Everything in this rifle build is pretty high quality. The only thing I compromised on is buying the BA barrel instead of the Krieger barrel I wanted. I am not using this rifle in any competitions so what is allowed is a non issue. It is for my personal satisfaction.

SO back to the question:
How is a slower to unlock bolt going to help with the signs of over pressure? please explain the theory? as for over gassed my shells eject at 3 to 330 with all ammo i have shot. It is my understanding that this is an indication of the appropriate amount of gas?

My AR15 works as good as any highend AR. And yes ARs are lots of fun! I have always loved the platform, that is why I chose to build instead of buy both a 15 and 10!

Ahh apologies, I was referring to your original post and that of the extractor shavings. I completely missed the bulged primer comment in that post.

Very simple! Two problems happening at the same time. I'd love to help, but as I was referring to your original post, and to answer all potential problems and signsosigns pressure signs; well all I can say is that answers are out there. I'm sure I can provide a list of manufacturers of components to suggest other people know how to build parts, but to assemble them into a functional device is all on me. Best of luck to you and please be safe, excuse me as I'm going to bow out now.

-Mac

 

[Normandinpatriot]

Ahh apologies, I was referring to your original post and that of the extractor shavings. I completely missed the bulged primer comment in that post.

Very simple! Two problems happening at the same time. I'd love to help, but as I was referring to your original post, and to answer all potential problems and signsosigns pressure signs; well all I can say is that answers are out there. I'm sure I can provide a list of manufacturers of components to suggest other people know how to build parts, but to assemble them into a functional device is all on me. Best of luck to you and please be safe, excuse me as I'm going to bow out now.

-Mac

thanks mac86951

 

[Michael C]

Here is what I believe the purpose of keeping the bolt locked a fraction longer... it helps pressure to subside just a bit more. Having the case expanding while it is being extracted is what often happens with M14/M1A rifles. There is not a good way to slow them down. But, with the AR platform you can do the few things mentioned to help that. I also suspect that the firing pin hole in your bolt is too big. It’s in spec but it is causing the primers to flow and pierce. I have a JP high pressure bolt and dont have that issue. If me shooting a 185 Berger with 44g of Varget is not piercing primers it has to be the combination of my bolt/firing pin fit, and the heavy buffer/spring. I am actually surprised that the ammo you are shooting would produce that much pressure. There was an older lot of that ammunition that was loaded with canister grade RL15 and the military had problems with it being too hot/high pressure. They switched to a different powder (some say 4064 type) and it went away. I would suggest you pull a bullet and weigh how much powder of whatever kind is in there just to get an idea of what you have. If it’s up near 44g that may just be too hot. If it is around 41-42g then of pretty much anything then it would be fine. This is government ammunition so it does not have anything super exotic in it.

 

[Michael C]

Not sure if you can see this very well, but, the cases on top were my 185 load with a standard weight buffer and spring. The ones in the middle were with the heavy buffer and spring, and the ones on the bottom were heavy buffer/spring and a tuned gas key.

 

[Normandinpatriot]

Here is what I believe the purpose of keeping the bolt locked a fraction longer... it helps pressure to subside just a bit more. Having the case expanding while it is being extracted is what often happens with M14/M1A rifles. There is not a good way to slow them down. But, with the AR platform you can do the few things mentioned to help that. I also suspect that the firing pin hole in your bolt is too big. It’s in spec but it is causing the primers to flow and pierce. I have a JP high pressure bolt and dont have that issue. If me shooting a 185 Berger with 44g of Varget is not piercing primers it has to be the combination of my bolt/firing pin fit, and the heavy buffer/spring. I am actually surprised that the ammo you are shooting would produce that much pressure. There was an older lot of that ammunition that was loaded with canister grade RL15 and the military had problems with it being too hot/high pressure. They switched to a different powder (some say 4064 type) and it went away. I would suggest you pull a bullet and weigh how much powder of whatever kind is in there just to get an idea of what you have. If it’s up near 44g that may just be too hot. If it is around 41-42g then of pretty much anything then it would be fine. This is government ammunition so it does not have anything super exotic in it.

The first 20rds i shot in the rifle were Hornady 168gn and absolutely no signs on the cases, the next 20 were Sig OTM 175gn and the cases, and no again no signs on the cases...Yes I to was very surprised to see the pierced primers, and ejector marks. The ammo was LC 19 stamped M118LR 175gn with worst primers and ejector marks, 20rds all bad. I shot 5 Lapua 308 with 168gn and the primers were all fine, but still had ejector marks. I will check out the ammo and weigh the powder and also see how much space is around the firing pin. I have already started looking at a heavier buffer...Will purchase in the next day or so and will update as i get more results and info. Thank you very much for assistance and advice!

 

[Michael C]

Good luck, keep us posted!

 

[Normandinpatriot]

Good luck, keep us posted!

Heavy buffer and spring purchased from heavybuffers.com (5.5oz) and JP high pressure bolt assembly from jprifles.com... I will update after the next test firing... I am also going to have friend who has a factory DPMS rifle try some of this M118LR and see how the cases look...

 

[Normandinpatriot]

Update... I received and installed my heavy buffer and the spring that was recommended to use with it. I only fired 2 rounds, 1, M118LR and one Lapua 168gn 308. Both cases seem to show less ejector mark. Both primers were still a little flattened, and the M118LR primer was popped...
Still waiting for the JP Rifles high pressure bolt...

I did pull a bullet from the Lapua and weigh the powder...44.4gns

the M118LR 41.1grns...

Both shells seemed full enough to be a compressed load, but only slightly. Image 2928 is the powder from the Lapua round and the powder from the M118LR is in image 2929...

The only scale I have at this time is an old school RCBS 1010 balance....

 

[Michael C]

Do you happen to know what chamber was used in your rifle? I wonder if you have a short chamber and that is causing pressure issues as well. For example, an Obermeyer chamber is shorter than a standard 308. A 168SMK at 2.80 in mine was just touching. I have to load them 2.780. Do you have a way to measure that such as the Hornady tool?

 

[Normandinpatriot]

Do you happen to know what chamber was used in your rifle? I wonder if you have a short chamber and that is causing pressure issues as well. For example, an Obermeyer chamber is shorter than a standard 308. A 168SMK at 2.80 in mine was just touching. I have to load them 2.780. Do you have a way to measure that such as the Hornady tool?

I do not know for certain what chamber... The barrel is a Ballistic Advantage Heavy Profile Premium Barrel 18" 1:10 308win. https://www.ballisticadvantage.com/18-inch-308-fluted-rifle-ss-premium-barrel.html I would like to assume it is the standard 308win chamber, but we all know what "assume" means... I do not have a way to measure the chamber unless "fire formed" brass works... I am waiting for Amazon to deliver my new calipers, as my old ones are not accurate.

For what its worth I had my friend fire 3 of each(m118 and lapua) in his DPMS and the ejector marks were worse than from my rifle prior to the buffer weight and spring swap. I am still waiting on the JP High Pressure bolt...

 

[Normandinpatriot]

Do you happen to know what chamber was used in your rifle? I wonder if you have a short chamber and that is causing pressure issues as well. For example, an Obermeyer chamber is shorter than a standard 308. A 168SMK at 2.80 in mine was just touching. I have to load them 2.780. Do you have a way to measure that such as the Hornady tool?

Finally got the JP high pressure bolt... Here is what the base of 3 cartridges fired today look like...
Here are three cases fired with the new bolt and buffer weight combo... Left to right... M118LR least damage to one yet, but the primer is flattened somewhat and the firing pin dent has been pushed back flush with the main primer base. Also the least notable ejector mark on any of the M118 i have shot yet. Middle case is a Lapua 167gn. It looks totally fine, these 2 rounds were my gun room and around 68-70 degrees when fired. On the right is another 167gn Lapua, it was in my truck all day and was quite warm when fired(i guess in the 85-90 degree range)It has a barely noticeable ejector mark and a slightly flattened primer.

It looks like I will be good to shoot the Lapua rounds now. Perhaps I should have gotten the 6.8oz buffer instead of the 5.5... Any thoughts?

 

[J-rod]

So I have a Gen 2 DPMS LR (24" SS bull barrel, technically chambered in 7.62x51). I was having this same issue, even with FGMM. I tried everything, adjustable gas block, heavy buffer (up to max of 6 tungstens), Tubbs spring, etc. It always seems the first round out the mag is the best (still has heavy ejector plunger markings), then the second, third and so on show severe pressure signs. The gun is a hammer but it chews brass up so bad it will leave bits of it in the action and such as I fire rounds. I had DPMS look at it and they said "it's normal brass markings", but I disagree. My neighbor has my old Gen 1 DPMS (that I really regret selling) and his brass looks perfect. I checked his brass against mine and since then have decided to give up on the rifle....why? Well my HS is .006"-.007" longer than his, which is a total .011"-.012" longer than off the shelf brass, as well as all my extra brass from my FTR rifle I was planning to recycle. A 308 go and no-go gauge will chamber but I don't have a field gauge to check. My math says it's right on the edge of being within 7.62 specs.
I don't really want to spend another dime on this dang thing but if you think this JP bolt will work, I may give it a try before a sell it? Thoughts? I assume it will fit?
Thanks for your post and sorry if I am hijacking it.

 

[Normandinpatriot]

So I have a Gen 2 DPMS LR (24" SS bull barrel, technically chambered in 7.62x51). I was having this same issue, even with FGMM. I tried everything, adjustable gas block, heavy buffer (up to max of 6 tungstens), Tubbs spring, etc. It always seems the first round out the mag is the best (still has heavy ejector plunger markings), then the second, third and so on show severe pressure signs. The gun is a hammer but it chews brass up so bad it will leave bits of it in the action and such as I fire rounds. I had DPMS look at it and they said "it's normal brass markings", but I disagree. My neighbor has my old Gen 1 DPMS (that I really regret selling) and his brass looks perfect. I checked his brass against mine and since then have decided to give up on the rifle....why? Well my HS is .006"-.007" longer than his, which is a total .011"-.012" longer than off the shelf brass, as well as all my extra brass from my FTR rifle I was planning to recycle. A 308 go and no-go gauge will chamber but I don't have a field gauge to check. My math says it's right on the edge of being within 7.62 specs.
I don't really want to spend another dime on this dang thing but if you think this JP bolt will work, I may give it a try before a sell it? Thoughts? I assume it will fit?
Thanks for your post and sorry if I am hijacking it.

No problem with the "Hijacking". My brass looks better with the heavier buffer and JP high pressure bolt. I am still waiting for my adjustable gas block. It sounds like your barrel extension/ chamber are the real problem. I havent had a chance to get back to the shop i deal with for a re-inspection with the go no go gauges yet and my new calipers should be in from amazon today so I will finally be able to get some measurement...
If i my rifle is still only in spec with the field gauge i will be returning the Ballistic Advantage barrel I have and getting Kreiger. They require you send the actual bolt you will be using and set the headspace with that bolt to guarantee it is in spec.

 

[Normandinpatriot]

Finally got my adjustable gas block! Unfortunately it didnt seem to make much difference. There is no noticeable difference in the brass with gas block fully closed or wide open. I am beginning to think that this ammo is to "hot" for my rifle or there is another issue...(m118lr and Lapua 167gn)

 

[J-rod]

Well by the grace of God, my old boss was willing to trade my old Gen 1 for my Gen 2. He was well aware of the issues but will never reload and just wants it to go bang when the zombies come.
So I took my standard load out with my old Gen 1. Proof is in the pics. I think having .006-.007” less HS and more surface area on the bolt (gen1 has one ejector plunger vs two on the Gen2), the pressure signs have gone away. My Gen 2 with all the works still chewed up brass...this Gen 1 only has a trigger and scope mounted. It’s a hammer like the Gen 2, but doesn’t chew up my brass.
5 shots at 100 through the mag, flier is last round. 42gn H4895, FC brass, 175 smk.