Why such big ejector marks?

[bigdawg86]

I have a home grown LR308 in Creedmore and I have a few questions. Went shooting last week and had a great trip, made hits at 1 mile!!!

Anyways, my brass was getting large ejector marks, some even have a little sliver of brass shearing. I was using Hornady 140g ELD match. I do not think it's a pressure issue. I have a 24" Lilja with rifle length gas tube with adjustable gas block, JP LMOS with the high pressure (small) firing pin. I know that semi-auto is inherently hard on brass, but I want to see what ya'll think about my "problem". The rifle ran fine without any feeding or ejection issues, last round bolt held open just fine.

When I first built the gun I did the routine of closing the gas block and slowly opening it until last round bolt hold open, so it was at one point tuned right.

[fawndog]

Dirty chamber, too much lube ?

[Pofoo]

I think your comment about the adjustable gas block puts you on the right track. It could be that the bolt is traveling back faster/harder do to the rifle wearing in, the recoil spring taking a set, etc.
Possibly soft brass with your current ammo?

[bigdawg86]

I think your comment about the adjustable gas block puts you on the right track. It could be that the bolt is traveling back faster/harder do to the rifle wearing in, the recoil spring taking a set, etc.
Possibly soft brass with your current ammo?

I am wondering the same... I'm still open to suggestions, but next time I go out I will dial the block down to where its at minimum but still functions.

[Tommy Gun]

What's your charge. I went as high as 42.5 (could have added more) but mines a bolt action. I had some Mark's on my 308 casings out of a M&P 10 and I dialed down the powder and have been fine ever since. Could be seating but I'm sure you found the lands or based it on factory ammo COL??

[Tommy Gun]

Oops 42.5 h4350. I use win 748 for my 308 plinking loads.

[FeuerFrei]

Sign of slight over pressure.
Check the case rims for extractor marks too. That's probably where the brass slivers came from.
Dial back the gas a tad and test again.

*try another brand of brass and see if you're just dealing with soft cases for manual bolt guns. Semi autos are rough on brass that's not designed/annealed for them. Military vs commercial ammo. Some brass seems softer/harder from different makers.

[bigdawg86]

What's your charge. I went as high as 42.5 (could have added more) but mines a bolt action. I had some Mark's on my 308 casings out of a M&P 10 and I dialed down the powder and have been fine ever since. Could be seating but I'm sure you found the lands or based it on factory ammo COL??

Initially was running 40.5 grains IMR 4551 under 140g Barnes Matchburner with Winchester LRP. I was running to lands but ran into magazine feeding issues, but that's irrelevant to the ejection marks. This was with converted LC 308 brass. This had ejector marks but nothing like pictured.

The brass pictured is factory Hornady 140g ELM.

[John Browning]

That's signs of overpressure.

[ar15barrels]

my brass was getting large ejector marks, some even have a little sliver of brass shearing.
I was using Hornady 140g ELD match.
I do not think it's a pressure issue.
I have a 24" Lilja with rifle length gas tube with adjustable gas block, JP LMOS with the high pressure (small) firing pin.
I know that semi-auto is inherently hard on brass, but I want to see what ya'll think about my "problem".
The rifle ran fine without any feeding or ejection issues, last round bolt held open just fine.

When I first built the gun I did the routine of closing the gas block and slowly opening it until last round bolt hold open, so it was at one point tuned right.

Load is too hot for that barrel/bolt setup.
If you could get a bolt with a smaller ejector hole size, it should not flow as much brass into the ejector hole.

You are probably running ammo designed to run in a bolt action.
Bolt actions can run slower powders to get higher muzzle pressures.
That same ammo will give you too much port pressure on an autoloader so the gun tries to unlock too quickly.

You say you adjusted the gas system, but was that with this same ammo or a different load?

[bigdawg86]

Load is too hot for that barrel/bolt setup.
If you could get a bolt with a smaller ejector hole size, it should not flow as much brass into the ejector hole.

You are probably running ammo designed to run in a bolt action.
Bolt actions can run slower powders to get higher muzzle pressures.
That same ammo will give you too much port pressure on an autoloader so the gun tries to unlock too quickly.

You say you adjusted the gas system, but was that with this same ammo or a different load?

The Ammo was Hornady 140g ELM. I did run my reloads same day, but they were loaded a little too long trying to be closer to the lands and had feeding issues, hence switching to Hornady. The reloads had minimal ejector marks, but nothing like this (140g Barnes Match Burner, 40.5g IMR 4551, WinLRP, 2766 FPS Average).

Now that I think about it I adjusted the gas system on reloads which ran 120g bullets and lower end powder loads... so running full loads I may need to readjust the gas block too.

You mention a smaller ejector... is that something you can suggest? I knew the firing pin needed to be smaller (hence the JP high pressure bolt), but was unaware of the ejector being a possible issue either.

Looking at my load data log, I don't know why I was running 40.5g as 40.0g gave me SD 8.9 which is fantastic... so I will drop my charges to 40.0g even, then readjust gas system.

[John Browning]

I did the same thing in a 6.5 Grendel. It is exactly what Randall said, the ammo is not tuned to that gas port/buffer weight/spring rate.

That brass is best trashed IMO. I loaded my Grendel brass after the same thing. I learned the not so hard but almost really hard way that it is cheaper to trash the brass than toss the dice.

[bigdawg86]

I did the same thing in a 6.5 Grendel. It is exactly what Randall said, the ammo is not tuned to that gas port/buffer weight/spring rate.



That brass is best trashed IMO. I loaded my Grendel brass after the same thing. I learned the not so hard but almost really hard way that it is cheaper to trash the brass than toss the dice.

Well I have the JP self captured buffer spring, so would having a heavier spring help or would I be better off dialing the gas down?

Sent from my SM-G950U using Tapatalk

[ar15barrels]

Well I have the JP self captured buffer spring, so would having a heavier spring help or would I be better off dialing the gas down?

Dial the gas down.
Spring tension is the LAST thing you adjust after gas volume and buffer weight.

[bigdawg86]

Dial the gas down.
Spring tension is the LAST thing you adjust after gas volume and buffer weight.

Thanks Randall, I will start over with the gas block next time I go shooting.