LR308 case marks after firing?

[Normandinpatriot]

I have some questions about typical marks on cases from LR/AR 308 rifles. I am new to this weapon system, but not to reloading.
I just finished my LR308 build and broke the barrel in with factory ammo. After firing the first round I inspected the case for signs of any type malfunction. I found what looks to be a small amount of material shaved of the base of the case by the extractor. On the neck of the case I found 2 small indentations. I assume these marks are caused when the case is being extracted and is being smashed into the lugs of the barrel extension. I took pics but the quality of the photos is crap and not worth uploading.
Mt questions:
1. Is this normal with this weapon platform?
2. Should I worry about these small dents on the neck if i am reloading?

 

[divingin]

Neither is all that unusual. Any problems the neck dents could cause will likely be ironed out when the neck goes through the sizing die (external problems) or when the expander ball is drawn through (internal.)

The shaving of the rim can probably be alleviated by pulling the extractor and smoothing and radiusing the edges.

If the ammo is not what you'll be using long term, I wouldn't worry too much about either of them at this point. Fix whatever problems you have when you get to your normal load.

 

[Wolfdawg]

Yes, these are normal Mark's and dents from an AR rifle. The dent near the shoulder is from the deflector extension behind the ejection port. The brass is thrown out, flips back and hits the deflector. If you look at it, you'll see brass marks on it.
You definitely need to inspect the brass every time. If they get cracked or too deformed, you will have trouble.
Reloading for a semi auto has its challenges. Be careful and do some research specific to your shooting style.
Hope this helps

 

[Normandinpatriot]

Thanks Divingin and Wolfdawg.
The extractor mark showed up of the one round I just chambered and ejected by hand. I did inspect the extractor when i cleaned the BCG after getting home from the breakin. It did not seem excessively sharp, or have a burred edge. Surprisingly there were no marks from the shell deflector. The 2 tiny dents on the neck look as though i should maybe do something to "soften" the edge of the lugs on the barrel extension that are inline with the extractor as the dent are pretty sharp edged.
The spring for the extractor is super strong... I need to put the bolt in a vice or squeeze it with padded pliers to get the pin out and was thinking the mark on the base was from chambering and not extraction.
I will re-inspect but I am not sure I want to "polish" or "buff" off the edge of the extractor. The BCG is a Lantac Enhanced BCG coated with NiBo. As for the lugs in the barrel extension I might do a light polish with a stone there
Again thanks!

 

[Dave in WI]

This platform seems to often be "overgassed" and tough on brass (extractor marks, ejecting at 2:00, etc). Usually solved with adjustable gas block.

 

[Uncle Ed]

I would buy some bulk once fired Lake City 7.62 brass for your AR, this brass is made of harder brass. "Its made Ford Truck tough" and it does not hurt as much if you loose a case or two.

 

[Normandinpatriot]

This platform seems to often be "overgassed" and tough on brass (extractor marks, ejecting at 2:00, etc). Usually solved with adjustable gas block.

It seems as though my rifle is ejecting at 3:00-4:00. The recoil impulse is actually less sharp than I anticipated. Perhaps due to the muzzle brake? The BCG I am using is quite heavy and supposed to help slow down the bolt cycle time...

 

[Normandinpatriot]

I will try some but i want to shoot this rifle out to 1000m or so. So i was hoping to use good quality cases like Lapua) for reloading.

 

[LGKLAS]

Norman, I shoot that platform in 6.5 CM. It is hard on brass, as others have noted. I reload using Hornady brass and Lapua. But, do not use Lapua in my semi-auto. Hornady brass will get you out to 1000 and spare you the wear and tear on your Lapua brass.

 

[Michael C]

I just finished building an LR308 (DPMS) platform M110 service rifle. I shot it last weekend at 1000. No problem with the right bullets and load. The system is fortunately very stout, and from what I have been told by the AMU guys is that you can use bolt action rifle loads. Of course you have to have the right chamber. But, I am using Berger 185’ and they had great elevation with a 4.5x scope on Saturday. I am using a heavy buffer and spring from Heavybuffers.com (over priced but it works so what can I do?). My 1000 yard brass was LC15 once fired machine gun brass that I small based sized, weight sorted and used some old Wolf LR primers. SD was 10.7 on a shot marker E target. On Tuesday I learned about an adjustable gas key (I had never heard of it before even though they have been around for several years) and purchased one. Should be here next week. I want it because even with the heavy buffer and spring, my brass with the 185’s is looking like it is probably a one and done. I got mine from Rubber City Armory, but, there are others that make the same product. Since I cant have an adjustable gas block due to NRA/CMP rules, this is the next best thing and it is cheaper at about 50 bucks. From what I have read, it works almost as well as an adjustable gas block.

 

[Rsadams]

Although completely normal for an AR platform , you could try 1step heavier buffer to help slow down the bolt...

 

[Uncle Ed]

Save $$ By Using Lake City 5.56x45mm Once-Fired GI Brass
http://bulletin.accurateshooter.com/2019/10/save-by-using-lake-city-5-56x45mm-once-fired-gi-brass/

Accuracy Potential of Mil-Surp 5.56×45 Brass
So, how accurate can previously-fired GI surplus brass be in a good National Match AR-15? Well, here’s a data point from many years ago that might be of interest. A High Power shooter who wrote for the late Precision Shooting magazine took a Bill Wylde-built AR match rifle to a registered Benchrest match. His first 5-round group ever fired in a BR match was officially measured at 0.231″ at 200 hundred yards. This was fired in front of witnesses, while using a moving target backer that confirmed all five rounds were fired.

He recounted that his ammo was loaded progressively with factory 52gr match bullets and a spherical powder using mixed years of LC brass with no special preparation whatsoever. Obviously, this was “exceptional”. However, he had no difficulty obtaining consistent 0.5-0.6 MOA accuracy at 200 yards using LC brass and a generic “practice” load that was not tuned to his rifle.

 

[Coyotefurharvester]

I put the fuzzy 1/2 of adhesive backed Velcro on the brass defector, helps with the neck dents.

 

[Normandinpatriot]

View attachment 1181949 View attachment 1181949 I just finished building an LR308 (DPMS) platform M110 service rifle. I shot it last weekend at 1000. No problem with the right bullets and load. The system is fortunately very stout, and from what I have been told by the AMU guys is that you can use bolt action rifle loads. Of course you have to have the right chamber. But, I am using Berger 185’ and they had great elevation with a 4.5x scope on Saturday. I am using a heavy buffer and spring from Heavybuffers.com (over priced but it works so what can I do?). My 1000 yard brass was LC15 once fired machine gun brass that I small based sized, weight sorted and used some old Wolf LR primers. SD was 10.7 on a shot marker E target. On Tuesday I learned about an adjustable gas key (I had never heard of it before even though they have been around for several years) and purchased one. Should be here next week. I want it because even with the heavy buffer and spring, my brass with the 185’s is looking like it is probably a one and done. I got mine from Rubber City Armory, but, there are others that make the same product. Since I cant have an adjustable gas block due to NRA/CMP rules, this is the next best thing and it is cheaper at about 50 bucks. From what I have read, it works almost as well as an adjustable gas block.

Nice shootin' Mike C.
I just got done shooting some Lake City M118LR. It is marked LC 19 on the base.I was only shooting at 100yds. I dont even want to talk about my poor performance today. I want to talk about OVER PRESSURE signs on the cases. I shot 20 rounds. I loaded a full mag to test the magazine as it seemed the follower suffered from tilting and jamming up so rounds might not feed. This happened, I purchased 3 ASC mags and they all seem to have the same shitty followers...

Now the important shit... I didn't inspect the casings until I fired all 20 of the M118lr I had loaded into the mag. As soon as i picked up the first round i noticed where the firing pin struck primer was hole.... As i collected the brass I noticed all of them had over pressure signs on the primer and most had mild half moon marks from the ejector. The package these rounds came in stated a MV of 2950...

For breaking in the barrel I used Sig Elite Performance 175gn OTM and 168gr, Hornady American hunter. Neither of these had any signs of over pressure and it was at least 20 degrees hotter out that day...

The sig ammo gave a MV of 2600 so I certainly was thinking I would get over pressure signs today...

 

[Normandinpatriot]

I put the fuzzy 1/2 of adhesive backed Velcro on the brass defector, helps with the neck dents.

Coyotefurharvester, I dont have any dents from the shell deflector, but that would be a good idea. I have "shave" marks from the extractor going over the base on the into battery and 2 small gouge/ dents on the neck that appear to be caused from the shell being smashed into locking lugs on the barrel extension during extraction after firing.

 

[Michael C]

Coyotefurharvester, I dont have any dents from the shell deflector, but that would be a good idea. I have "shave" marks from the extractor going over the base on the into battery and 2 small gouge/ dents on the neck that appear to be caused from the shell being smashed into locking lugs on the barrel extension during extraction after firing.

I do use a heavy buffer (6.2 oz carbine buffer), a heavy spring and they help a bunch. I also just installed an adjustable gas key on the bolt carrier (Rubber City Armory).

 

[Normandinpatriot]

I do use a heavy buffer (6.2 oz carbine buffer), a heavy spring and they help a bunch. I also just installed an adjustable gas key on the bolt carrier (Rubber City Armory).

Although completely normal for an AR platform , you could try 1step heavier buffer to help slow down the bolt...

I will look into this. I am not sure i understand how holding the bolt closed longer (i understand we are talking micro-seconds) will help? Could you please explain a little so I understand the logic/ theory?

 

[mac86951]

I will look into this. I am not sure i understand how holding the bolt closed longer (i understand we are talking micro-seconds) will help? Could you please explain a little so I understand the logic/ theory?

Adjustable gas blocks, adjustable gas keys, buffer weights, heavier buffers, and stronger springs are all devices to change the "timing" of the rifle, in this case to delay the bolt carrier rearward movement by providing less force, or increasing inertia a d thereby allowing the brass that additional fraction of a second to reduce pressure and thereby grip on the chamber wall. I think these suggestions are completely valid, but I do see nomenclature confused often. All of these devices are to reduce case head swipe which is a shaving or marking of the case head as the ejector is rotated across it. As you've mentioned that the extractor is shaving the case head, that would be from the rim of the case. This is usually to a rubber extractor buffer installed wrong, or maybe deformed, or otherwise too stiff. There are some tuning adjustments you can make to your extractor, but may just need a new spring / buffer or to remove some gunk left behind from the NiBo process.

If rules allow I do recommend an adjustable gas block, or some such tuning on the gas system to enhance the life of the brass. Likewise, some LR308 will lunch primers with factory ammo, usually due to excessive firing pin and bolt hole slop. Harder primers, or better bolt (or JP enhanced bolt) could resolve that if you really need more velocity.

Extractor problems, case head swipe, COL or seating depth, and brass sizing are the biggest AR loading issues beyond that of a bolt action.

Gas system timing can change the scale value of the first two; COL is what feeds from.the magazine if you're not single loading, and sizing to push shoulders 0.003-5" and maybe a small base die are common answers to those problems. I see no reason to fix them until they become a problem; this my recommendation on your bolt is to check the spring / buffer under the extractor and bolt recess of extractor for burrs.

Welcome to ARs, they are lots of fun!

-Mac

 

[Rsadams]

I will look into this. I am not sure i understand how holding the bolt closed longer (i understand we are talking micro-seconds) will help? Could you please explain a little so I understand the logic/ theory?

I think the above post by mac86951 explains alot about the different ways to tune your AR.... Most guns are way over gassed anymore and that is a problem in it's own... SPRINCO springs out of Austin TX is a great spring company that sells tons of stuff for tuning ARs IE springs and buffers that will last so long you will burn through more than one rifle before the springs need changing... A carbine length gas system will beat the gun to death over time especially if it's over gassed but you can do somethings to help alot... I tune for rifle life , not so much brass life because the AR is normally very hard on brass....

 

[Normandinpatriot]

Adjustable gas blocks, adjustable gas keys, buffer weights, heavier buffers, and stronger springs are all devices to change the "timing" of the rifle, in this case to delay the bolt carrier rearward movement by providing less force, or increasing inertia a d thereby allowing the brass that additional fraction of a second to reduce pressure and thereby grip on the chamber wall. I think these suggestions are completely valid, but I do see nomenclature confused often. All of these devices are to reduce case head swipe which is a shaving or marking of the case head as the ejector is rotated across it. As you've mentioned that the extractor is shaving the case head, that would be from the rim of the case. This is usually to a rubber extractor buffer installed wrong, or maybe deformed, or otherwise too stiff. There are some tuning adjustments you can make to your extractor, but may just need a new spring / buffer or to remove some gunk left behind from the NiBo process.

If rules allow I do recommend an adjustable gas block, or some such tuning on the gas system to enhance the life of the brass. Likewise, some LR308 will lunch primers with factory ammo, usually due to excessive firing pin and bolt hole slop. Harder primers, or better bolt (or JP enhanced bolt) could resolve that if you really need more velocity.

Extractor problems, case head swipe, COL or seating depth, and brass sizing are the biggest AR loading issues beyond that of a bolt action.

Gas system timing can change the scale value of the first two; COL is what feeds from.the magazine if you're not single loading, and sizing to push shoulders 0.003-5" and maybe a small base die are common answers to those problems. I see no reason to fix them until they become a problem; this my recommendation on your bolt is to check the spring / buffer under the extractor and bolt recess of extractor for burrs.

Welcome to ARs, they are lots of fun!

-Mac

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!