LMT MWS – Ejected Cases With Cut Marks

[Fire4EffectCA]

I installed a new LMT 20” 6.5mm Creedmoor barrel on my LMT MWS and took it out to the range today. No malfunctions, but I noticed groves being cut in the case necks. These are appearing on the extractor side of the case. I am guessing these are coming from the inside of the barrel extension on the extractor side. The bolt has duel extractors and I believe the extracted fired cases are being pulled hard against the inside of the barrel extension and there must be sharp edges cutting into the necks. Has anyone seen this before? I am wondering if the cases are not suitable for reloading. I have not noticed this on cases ejected from my 308 MWS.

NOTE: I did cycle several unfired cartridges through the rifle. No marks were left. On the bullets or cases.

Ammo: Hornady American Gunner 6.5 Creedmoor 140 gr HPBT

I measured ten random cases with a RCBS Case Gauge

Measurements Before Firing
Four at +0.001
Three at 0.000
One at -0.001
Two at -0.002
Three at -0.003

Measurements After Firing
Four at +0.005
Four at +0.007
Two at +0.008

I don’t have a No Go gauge for 6.5 mm Creedmoor and I am wondering if +0.007 and above is heading in the No Go area.

 

[Ledzep]

Maybe not to that level of severity, but literally every AR pattern rifle puts those marks on cases.

 

[bllistc]

Yea that’s how they look out of mine. Both with .308 and 6.5

 

[Snuby642]

Sharp feed ramps on mine looked like that. Would have been able to gut a pig with them and still have more polishing to do.

100 rounds of ruined brass.
Hand feed one in and fire, see what you get. Maybe the same barrel extension vendor I got on my 6.5g.

 

[Fire4EffectCA]

Maybe not to that level of severity, but literally every AR pattern rifle puts those marks on cases.

My SR-25 does not impart those marks and neither does any of my Colts. I will try and find brass from my LMT LM8MRP to see if they have similar marks.

 

[Fire4EffectCA]

Sharp feed ramps on mine looked like that. Would have been able to gut a pig with them and still have more polishing to do.

100 rounds of ruined brass.
Hand feed one in and fire, see what you get. Maybe the same barrel extension vendor I got on my 6.5g.

Is it possible polish the interior edges in the barrel extention?

 

[Bigjake83]

Is it possible polish the interior edges in the barrel extention?

Those marks are from the locking lugs on the barrel extension. When the gases propel the BCG rearward and rips the case from the chamber the force of your extractor scraping the case across the barrel extension lugs right before it slings it out the ejection port.

You can polish them and it will help, I always ask for this to be done when I have a new barrel spun up, the design of the bolt also has some influence on this phenomenon as well. It's honestly not a big deal, large frame AR are just harder on brass.

 

[Ledzep]

My SR-25 does not impart those marks and neither does any of my Colts. I will try and find brass from my LMT LM8MRP to see if they have similar marks.

223 and 6 arc... Every AR I've owned has done it. 223, grendel, 308, 6.5 cm... Can ID what weapon fired range pick up brass from it.

 

[Fire4EffectCA]

223 and 6 arc... Every AR I've owned has done it. 223, grendel, 308, 6.5 cm... Can ID what weapon fired range pick up brass from it.

I have brass bagged identifying which rifles it was fired from. Both of the SR-25's I have shot did not have the marks. I did find some brass from my 308 MWS and it had the marks, but they were very small and light. It was difficult to find any 223 brass with the marks, but the ones I did find were very small and light.

Sounds like I need to find a good way to polish the backside of the lugs in the barrel extension. I do have a new 308 MWS barrel and the backside of the lugs inside that barrel extension feel smooth. I will compare to the 6.5 mm creedmoor barrel extension tomorrow.

 

[Snuby642]

My bad, these marks are on the shoulder and nearly 100% sure its the razor sharp feed ramp edges.

Going to pull the damn barrel to polish them more. Damn it.

 

[troupe]

Polish the sharp edges and also think about adjustable gas ?

 

[GBMaryland]

My Larue OBR circa 2010 does not do that.... But it doesn’t really look that bad on those cases.

Those can still be resized and used... i’ll be a little more concerned about the denting of the cases

 

[Fire4EffectCA]

Polish the sharp edges and also think about adjustable gas ?

I am not aware of any adjustable gas systems for the LMT MWS. I do have an adjustable gas system on my Stoner SR-25.

 

[tvalks]

Every one of the 6.5 rounds I fired looked like that to varying degrees, a lot much worse, most were dented as well. This is from one of the Black Friday 22" 6.5 barrels, with three different loads

 

[Fire4EffectCA]

Every one of the 6.5 rounds I fired looked like that to varying degrees, a lot much worse, most were dented as well. This is from one of the Black Friday 22" 6.5 barrels, with three different loads

My dents are further back, but I believe the dents are from the case deflector on the upper receiver too. I am hearing others are using adhesive backed velcro to reduce this. I wonder if reducing the spring tension on the duel ejectors would help. This rifle has a stock H3 buffer installed.

 

[GBMaryland]

If you want everything to be pristine almost all the time you’re gonna have to go out and buy a JP rifle

 

[Fire4EffectCA]

If you want everything to be pristine almost all the time you’re gonna have to go out and buy a JP rifle

Sounds like you don't reload.

 

[Fire4EffectCA]

Every one of the 6.5 rounds I fired looked like that to varying degrees, a lot much worse, most were dented as well. This is from one of the Black Friday 22" 6.5 barrels, with three different loads

How is the accuracy of your 22" barrel? I thought about getting one during the sale, but I already had purchased a 20" barrel.

 

[tvalks]

How is the accuracy of your 22" barrel? I thought about getting one during the sale, but I already had purchased a 20" barrel.

No Idea, don't have on optic for the rifle yet. I just took it out to function check it with Iron sights. Its seems pretty capable, everything was tight for 60rds of rapid fire.

 

[Fire4EffectCA]

No Idea, don't have on optic for the rifle yet. I just took it out to function check it with Iron sights. Its seems pretty capable, everything was tight for 60rds of rapid fire.

I keep getting three of four tight rounds and then I would throw one or two wide. The powder in the ammo I was shooting was really dirty. The bolt and carrier were caked with carbon. I have never seen so much build up after only 50 rounds. The bolt and carrier also had what looked like copper oxide mixed in with the carbon deposits. I had cleaned the rifle thoroughly before going to the range for the first time and it was spotless before shooting.

 

[troupe]

Is it D/I or piston, a D/I adjustable gas block should be able to be installed. Guessing that it is .750 barrel dia. under the gas block. I never had a LMT and am not aware how hard it is to remove the barrel. If it can be taken apart then a Adj. Gas could be added. The block would not have to be a LMT product, just would have to fit under the forearm.

 

[Fire4EffectCA]

Is it D/I or piston, a D/I adjustable gas block should be able to be installed. Guessing that it is .750 barrel dia. under the gas block. I never had a LMT and am not aware how hard it is to remove the barrel. If it can be taken apart then a Adj. Gas could be added. The block would not have to be a LMT product, just would have to fit under the forearm.

It is my understanding there are no adjustable gas blocks available for the LMT MWS.

 

[FF05]

Adjustable gas blocks won't work as MWS gas ports are drilled at an angle.

This is what i did to fix overgassing on my 308 barrel.

Remove the gas block (you may need to apply some heat), then drill and tap it for a long grub screw. Now it's adjustable, problem solved.

 

[Fire4EffectCA]

Adjustable gas blocks won't work as MWS gas ports are drilled at an angle.

This is what i did to fix overgassing on my 308 barrel.

Remove the gas block (you may need to apply some heat), then drill and tap it for a long grub screw. Now it's adjustable, problem solved.

I saw your previous post about your gas block modification when I was searching for information on gas adjustments on the MWS. Very impressive.

 

[oniak]

Adjustable gas blocks won't work as MWS gas ports are drilled at an angle.

This is what i did to fix overgassing on my 308 barrel.
View attachment 7418868
Remove the gas block (you may need to apply some heat), then drill and tap it for a long grub screw. Now it's adjustable, problem solved.

That is pretty slick right there. I like that a lot.

 

[Saf3sh00t3r]

Add an adjustable gas key.

RCA Adjustable Gas Key - Welcome to Rubber City Armory

Made from Pre-Hardened 4140: 28-32RC with radiused corners reducing sharp edges. Enhances performance of low mass and standard mass GI systems without unnecessary dissassembly. Gas flow is adjusted and maintained at the carrier with set screws. One to adjust gas flow and one to lock it in place...

rubbercityarmory.com

 

[Fire4EffectCA]

I decided to order the BRT EZTUNE Gas Tube.

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[Saf3sh00t3r]

I decided to order the BRT EZTUNE Gas Tube.

Black River Tactical Store - Shop BRT

Shop BRT Black River Tactical Store Covert Comp OPTIMUM EZTUNE Gas Tube MicroTUNE Gas Block CustomTUNE Gas Port MicroPin Gas Block Mk12 Gas Tube BRT EXT BRT EXC BRT PDW Pistol Carbine Mid Midlength Rifle Upper Receiver Group Bolt Carrier Group Barrels Muzzle Devices Adjustable Gas Drive AR15 LMT

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That’s nifty. Stupid question how do you adjust the gas? Replace the tube again?

The point would be that you’d want to adjust gas based on suppress/un-suppressed Or Hot/non-hot loads, wouldn’t it?

 

[Shoots 700's]

Yep, looks like mine out of a308. Thats why i don't use Lapua in a gas gun.

 

[Fire4EffectCA]

That’s nifty. Stupid question how do you adjust the gas? Replace the tube again?

The point would be that you’d want to adjust gas based on suppress/un-suppressed Or Hot/non-hot loads, wouldn’t it?

They recommend the opening size based on the information you provide them. I guess I will find out how well it works after I install it.