Lr-308 build gas and feeding issues

[Matman2010]

This quarantine has me digging through the safe trying to get guns figured out that I have had issues with. I built this LR-308 back in 2018 and its got some issues.

Specs:
DPMS LR-308 lower
DPMS BCG
DPMS Mags
DPMS Carbine Spring and Buffer
AR Stoner Upper Receiver
Rainer Arms 18" Ultra Match barrel
Rainer Arms .800 gas block

Now when I built this I did not have a suppressor but I was having these same issues when I first built it.

Issues:
1. Case necks are getting dinged from hitting the brass deflector and they are flying out around the 1 - 2 o'clock position.
2. Some times it seems like its short stroking and using friction pulling the next round out of the mag and then proceeds to smash the bolt through the side of the case. (Had this issue on my DPMS LR-243 and keeping it well lubed fixed it, doesnt seem to be working on this LR-308)

The first issue i beleive means that I need to put and adjustable gas block on it. Problem is Rainer used a .800 gas block on this barrel and they are the only ones that have gas blocks for them and they are all out of stock. There is only 1/8" material between the gas tube and the OD of the barrel. I have been thinking about drilling through the front of the gas block and put a set screw in there to restrict some of the gas. But I believe the biggest set screw I can put in there is a 4-40 screw which I don't believe would be big enough to cut the flow of gas off much. (I can't measure the port on the inside of the gas block, but it looks to be about 2x bigger than the hole in the barrel) I've also thought about getting a .750 adjustable gas block and either boring it out on the mill or lathe, but not sure if there is enough material for me to bore one out or not.

 

[rpoL98]

from the bottom of the gas block, you could tap that short channel in the gas block between the barrel journal and the gas tube. I've done that for an overgassed A2 FSB and for overgassed non-adjustable piston gas blocks. use a really short SS set screw, really short, and drill orifices in the set screw. Only tap to a depth of maybe 2 threads, so that the set screw bottoms out against the threads just short of the gas tube, instead of the gas tube itself. You can grind down the top of the set screw, the hex key receptacle, to just the minimum necessary to engage the hex key, you're not going to be putting a lot of torque on that little bugger. put a flat bottom on the bottom of the set screw. That helps to shorten the set screw to the right length.

similar in concept to the BRT system, but home-made. Since you have time on your hands...

I had to get a special tap with a necked-down shank since you have to run the tap through the existing GB set-screw holes. same thread size as your existing GB mounting set-screws.

https://blackrivertactical.com/WP/BRT-CustomTUNE-Gas-Port-HD-Install-Kit-p110100257

 

[shax2lex]

I think I’d start with an adjustable gas block and go from there.

 

[rpoL98]

here's 2 examples of the long-reach taps I was referring to. As examples only. You would have to select the tap thread that matched the existing set-screws in your current unusual-diameter gas block. BRT also has gas tubes with calibrated orifices.

bottom-tap
pointed tap

 

[ShooterwithNoName]

Have you considered going with a heavier buffer and spring? May help balance it out without getting into the gas block...

Heavy Buffers makes a heavy 308 DPMS carbine buffer. You could also switch to an A5 or Rifle length buffer tube to get more of a selection of buffers to choose from. I run an A5 length buffer tube (UBR) on my 308 and it allows me to run standard 556 carbine buffers rather than the short little 308 buffer.

A heavier buffer plus spring should help, maybe worth a try before you perform any surgery on the GB.

 

[bunsen27]

I just swapped barrels and gas blocks from the factory 24" w/ JP adjustable gas block to a Criterion 18" w/Seekins adj gas block (0.750"). It was an interesting experience trying to dial it in.

Do you happen to have a scale that weighs in grams? For reference my DPMS LR-308 buffer is 155gr.

A 0.800" gas block is indeed an oddity. Other than that option, my other recommendation would be looking into the JP Silent Captured spring system with variable weights and spring strengths to really fine tune the rifle. Yes, it is way too expensive for what it is, but it does work.

JP Rifles

www.jprifles.com

JP Rifles

www.jprifles.com

 

[Matman2010]

here's 2 examples of the long-reach taps I was referring to. As examples only. You would have to select the tap thread that matched the existing set-screws in your current unusual-diameter gas block. BRT also has gas tubes with calibrated orifices.

bottom-tap
pointed tap

Ill keep that in mind, probably going to mess with buffer and spring first before I start hacking up a part that is hard to find.

Have you considered going with a heavier buffer and spring? May help balance it out without getting into the gas block...

Heavy Buffers makes a heavy 308 DPMS carbine buffer. You could also switch to an A5 or Rifle length buffer tube to get more of a selection of buffers to choose from. I run an A5 length buffer tube (UBR) on my 308 and it allows me to run standard 556 carbine buffers rather than the short little 308 buffer.

A heavier buffer plus spring should help, maybe worth a try before you perform any surgery on the GB.

Ive thought about it. Thinking about ordering up one of Heavy Buffers 6.5oz buffer with springs. They say its best for suppressed rifles. And I cant see myself not running suppressed.

I just swapped barrels and gas blocks from the factory 24" w/ JP adjustable gas block to a Criterion 18" w/Seekins adj gas block (0.750"). It was an interesting experience trying to dial it in.

Do you happen to have a scale that weighs in grams? For reference my DPMS LR-308 buffer is 155gr.

A 0.800" gas block is indeed an oddity. Other than that option, my other recommendation would be looking into the JP Silent Captured spring system with variable weights and spring strengths to really fine tune the rifle. Yes, it is way too expensive for what it is, but it does work.

JP Rifles

www.jprifles.com

JP Rifles

www.jprifles.com

I do not have a scale that weighs grams.

Yeah, the .800 gas block is odd, not sure why Rainer Arms exactly chose that. They say its for making the barrel heavier but not to heavy. Wont be buying another one of these. Didnt really notice the gas block size when I bought it.

Im going to see about trying a Heavy Buffers buffer before I spend that kinda money on the JP stuff. I am sure it does work.

 

[Matman2010]

I did weight my buffer. 3.8 oz.

 

[rpoL98]

Im going to see about trying a Heavy Buffers buffer before I spend that kinda money on the JP stuff. I am sure it does work.

If you're running a 7" (inside depth) carbine buffer tube, both KAK and also Primary Arms/Expo have a more economical 2.5" 5.3oz buffer for 308 carbine use. Heavy Buffer's 308 carbine buffer spring at $15 is a good deal. JMHO.

Expo 5.3oz 308 carbine buffer at Primary Arms

 

[Matman2010]

If you're running a 7" (inside depth) carbine buffer tube, both KAK and also Primary Arms/Expo have a more economical 2.5" 5.3oz buffer for 308 carbine use. Heavy Buffer's 308 carbine buffer spring at $15 is a good deal. JMHO.

Expo 5.3oz 308 carbine buffer at Primary Arms

Thanks, went ahead and order the Heavy Buffers Car-10 XH 6.5 oz tho.

 

[bunsen27]

I did weight my buffer. 3.8 oz.

Ok, we can work with that!

There are 453g per pound, thus 453g/16 ounces = 28.3125g per ounce
28.3125 x 3.8 = 107.587g

That is a fairly lite buffer for a LR-308 running FGMM suppressed w/o an adjustable gas block.

For reference my 155gr buffer converts to 5.5ounce, and I'm running a Dead Air SandmanTi with the Seekins adj gas block 1/3 closed for FGMM. The buffer is spring is just a standard one with at minimum 2k rounds on it.

The above recommendation by @rpoL98 is spot on! I'd grab the heavy spring too just in case your suppressor generates a lot of back pressure.

It may not be 100% optimized, but it should run MUCH better than it does now, good luck.

 

[bfoosh006]

A heavier buffer is preferred in my setups... the 3.8oz buffer is to light typically.

I still run Adj. GB's in all mine... with Tubbs Flatwire 308 recoil springs in all buffer tube lengths, ...2.5" 5.3oz ( ? ) , 3.25" 5.4oz, and rifle buffer 9.3oz buffers, SLR Adj. GB's , Lantac brakes.

I would suggest you try phoning Rainer Arms... and asking if they have any .800 Adj. GB's that aren't listed on the webpage... explain your predicament.
Never hurts to try.

Ultimately restricting your gas volume, will be a gratifying , best bet solution. ( IMHO )

You also might consider asking Superlative Arms if they sell their "made for Rainer Arms" .800 Adj GB. to the public.

 

[Matman2010]

A heavier buffer is preferred in my setups... the 3.8oz buffer is to light typically.

I still run Adj. GB's in all mine... with Tubbs Flatwire 308 recoil springs in all buffer tube lengths, ...2.5" 5.3oz ( ? ) , 3.25" 5.4oz, and rifle buffer 9.3oz buffers, SLR Adj. GB's , Lantac brakes.

I would suggest you try phoning Rainer Arms... and asking if they have any .800 Adj. GB's that aren't listed on the webpage... explain your predicament.
Never hurts to try.

Ultimately restricting your gas volume, will be a gratifying , best bet solution. ( IMHO )

You also might consider asking Superlative Arms if they sell their "made for Rainer Arms" .800 Adj GB. to the public.

I did get a hold of Rainer Arms. They said they are being produced and no ETA on when they will be available. I plan on getting an adjustable gas block whenever I can get my hands on one.

 

[D1gger]

My build was putting a dent on the cases at the shoulder from hitting the deflector, with by AGB adjusted 1 click past holding the bolt open on an empty mag.
A little tape on the deflector pretty much eliminated the dent. Maybe not the preferred way, but it works.
I also would get those double feeds, but only when I tried to use a brass catcher. Once I ditched that, no issues

 

[2aBaC̶a̶]

The dented case looks like a short stroke. Does it lock back on the actual bolt catch or mag follower on the last round?

 

[Matman2010]

The dented case looks like a short stroke. Does it lock back on the actual bolt catch or mag follower on the last round?

View attachment 7294377

I was thinking it was short stroking when it dented the case. After it did this with two rounds(they were not back to back) I started single feeding them. And don't remember it not locking back, but I cant say that I paid attention to if it locked back on the bolt catch or the mag follower.

 

[Matman2010]

Got the 6.5oz buffer and spring in from Heavy Buffers. Got some 168 gr FGMM ammo from my cousin and took the rifle out to test it. Ammo fed fine into the rifle. I'm starting to wonder if my hand loads were causing the problem. the 168 gr are 2.8" long and I had my 175 gr hand loads a 2.81" long. They did not drag on the mag but Im thinking that was just to close to the mag to get them to feed correctly all the time.

Now ejection does not seem to have changed. As you can see in the picture there are 3 cases next to my bag and 2 just right off the mat. These are exactly where they fell. The bolt is not locking back on the last round. Not sure if its short stroking or a mag issue.

As for the 168 gr FGMM it has shot the best 5 round group out of this rifle. My hand loads with 168 gr Nosler CC and 175 gr Nosler CC where shooting around 2 - 2.5 moa. Not sure if these barrel just doesnt like the bullets or my powder choices are just to slim right now.

 

[D1gger]

After I put my suppressor on my 6.5, it ejected brass forward and dented the case. I took 2 clicks out of the gas block and they went back to a 3-4 o'clock position.

 

[Matman2010]

I do not currently have an adjustable gas block. They are currently 3 - 4 weeks out. I plan on getting one when they finaly come in stock. But the signs shown from the rifle right now seem to say its over gassed yet under gassed right now.

 

[corey4]

What gas block are you wanting to get?

 

[bfoosh006]

Frankly, where your brass is falling is great... if it was flinging it considerably further I'd worry about.

As for the not locking back... consider putting the OEM recoil spring back in and trying that with the 6.5oz buffer

And how many rounds through it so far?... as in it may need more break in.

I assume you can manually lock the BCG back, with a empty mag.

 

[bunsen27]

What's your hand load recipe? I load both the 168gr & 175gr Nosler in LC brass with CCI 43 or WLR primers over 43.5gr & 42.4gr of IMR4895 respectively for my LR-308.

 

[Matman2010]

Frankly, where your brass is falling is great... if it was flinging it considerably further I'd worry about.

As for the not locking back... consider putting the OEM recoil spring back in and trying that with the 6.5oz buffer

And how many rounds through it so far?... as in it may need more break in.

I assume you can manually lock the BCG back, with a empty mag.

I mean I like that the brass is falling there. I don't have to go find it. Just off that chart shown above that is not where the cases are suppose to be going.

Ill try the OEM spring next time.

Probably 100 so far on the barrel. The lower and bolt came from an LR-308 that someone took apart to steal the High Rise upper.

Yes

What's your hand load recipe? I load both the 168gr & 175gr Nosler in LC brass with CCI 43 or WLR primers over 43.5gr & 42.4gr of IMR4895 respectively for my LR-308.

I just broke out the IMR4895 this past weekend to try. 175 gr Nosler CC Hornady brass with CCI 200 primers and did couple loads between 37.5 and 38.5 gr of IMR4895 but Im pretty sure my 2.81 OAL caused the cases to feed wrong and messed up a couple rounds. You are over what nosler says for max on both. Do most company keep their load data toward the lower end? I tired some BL-C2 behind the 168 gr CC because that is the recipe I use for my R700 but when I got around the 44.5 grs that I use in the 700 I was getting pressure signs. Or the brass I was using was not in very good shape.

 

[bunsen27]

I just broke out the IMR4895 this past weekend to try. 175 gr Nosler CC Hornady brass with CCI 200 primers and did couple loads between 37.5 and 38.5 gr of IMR4895 but Im pretty sure my 2.81 OAL caused the cases to feed wrong and messed up a couple rounds. You are over what nosler says for max on both. Do most company keep their load data toward the lower end? I tired some BL-C2 behind the 168 gr CC because that is the recipe I use for my R700 but when I got around the 44.5 grs that I use in the 700 I was getting pressure signs. Or the brass I was using was not in very good shape.

That Nosler data is well under where people normally run with a 175gr & IMR4895.

A 168gr SMK over 41.5gr of IMR4895 in LC brass is a well know highpower load for the M1A.

The nodes tend to be ~1.0gr apart with the highest usable node around 44.X for commercial (Win or Rem) brass with Mil (LC) brass around 43.X

 

[bfoosh006]

I mean I like that the brass is falling there. I don't have to go find it. Just off that chart shown above that is not where the cases are suppose to be going.

Ill try the OEM spring next time.

Probably 100 so far on the barrel. The lower and bolt came from an LR-308 that someone took apart to steal the High Rise upper.

Yes

Bear in mind, and judging by the "distance" your fired cases are probably very lightly bouncing off the brass deflector.

If the fired cases were attempting a low altitude earth orbit.. I'd be concerned about the "o'clock" position.

But seriously, that short of a distance, implies a relatively soft ejection.

And if you happen to have a spare ejector spring... clip a coil from it, I'd bet your "o'clock" position would change.

 

[Matman2010]

That Nosler data is well under where people normally run with a 175gr & IMR4895.

A 168gr SMK over 41.5gr of IMR4895 in LC brass is a well know highpower load for the M1A.

The nodes tend to be ~1.0gr apart with the highest usable node around 44.X for commercial (Win or Rem) brass with Mil (LC) brass around 43.X

Thanks, Ill keep all this in mind trying new loads for it.

Bear in mind, and judging by the "distance" your fired cases are probably very lightly bouncing off the brass deflector.

If the fired cases were attempting a low altitude earth orbit.. I'd be concerned about the "o'clock" position.

But seriously, that short of a distance, implies a relatively soft ejection.

And if you happen to have a spare ejector spring... clip a coil from it, I'd bet your "o'clock" position would change.

Yeah they are. I noticed that but I guess I forgot about it. They are not all dinged up tho so that is great.