Adjustable gas block: ejection pattern or mag lock back?

[spife7980]

So I put together a cheap upper (my first ar) to shoot while I wait for my sbr papers to get back. I shot it a bit last weekend and tried to adjust the gas block but I noticed something that I had never considered before while setting it up.

• 16" cmmg midlength gas 5.56 barrel
• Wojtek adjustable gas block
• Toolcraft BCG
• JP H2 SCS
• Shooting with a brake mount omega
• Shooting the frontier 55gr fmj plinker ammo.

Ive read that the block should be adjusted until it locks back on an empty mag.
Ive also read that it should be adjusted to throw them out at 3-4 oclock.

My question is, what happens if those two factors arent at the same settings on the gas block? I first tuned it for mag lock back, no problem. I then noticed that it was throwing them at out back towards 5 oclock. I adjusted it open so that there was more gas bringing it up to 3 oclock and locked it back down. Once I finally got it locked up at that setting I shot a bit more and then went to collect my brass I noticed that they all had an ejector mark and a slight burr which is telling me that its over gassed.

So is it:
Better to be overgassed and fucking up my brass?
Or should I set it to just lock back on an empty mag and then just not worry about its ejection location?
Or is it that on the initial setting for first empty mag lock back the buffer is too heavy whcih is slowing it down enough to throw them at 5 and a lighter buffer would allow it to eject slightly sooner and that would locate them in the proper location?

 

[Foghornleghorn]

Lock back on an empty mag is minimum and gives you a starting point. Adjust with more gas until it ejects at 3:00 your brass will thank you. That brass shows to be a little on the warm side. The ejection at 5:00 indicates not enough gas. I used that same chart to make a buffer adjustment, don't have and adjustable gas block. Others mileage may vary.

 

[MontanaMan]

I'm not familiar with that gas block so I don't know haw finely it can be tuned.

Generally get the bolt to just lock back & then just a little more gas, usually gets ejection about right.

If it's just locking back & still ejecting at 5 o'clock & reliable, I'd not worry too much.

Different ammo may take a different adjustment, obviously.

MM

 

[Precision Underground]

I can’t imagine overgassing causing ejector marks. Over pressure will cause ejector marks, or just cheap crappy brass.

I believe the ejector mark is in the circle, the extractor mark is where you wrote ejector.

EDIT My bad I see you wrote "opposite the ejector mark". My guess is soft brass.

 

[Kadams1563]

Just tune is down as much as possible where it locks back on empty mag with PMC or whatever light loaded .223.

That chart needs to go away.

 

[Luvman]

Just tune is down as much as possible where it locks back on empty mag with PMC or whatever light loaded .223.

That chart needs to go away.

I Don’t run adjustable gas blocks on small frame ARs. I use the buffer weight for tuning.

I have a PSA mid length that won’t cycle Tula with a 3 oz buffer (std carbine) but runs .223 PMC fine and a BA midlength that is so over gassed it will lock back on Tula in 20 degree weather with a 5oz 9mm buffer

The only thing concerns me with the ejection pattern is when it’s between 1:00-2:00.

Both my midlength barrels eject between 3:00-5:00

Test your rifle in the winter with low pressure ammo like PMC. If it’ll run low pressure ammo when it’s cold it’ll run anything.

I also run moly based dry lube.

 

[winniedonkey]

Did you test it with out the omega on?

 

[spife7980]

I did shoot without the omega for the first few just to verify that they were coming out straight but if I have to shoot this thing without the can on it I’d rather just throw it in the trash.

And thanks for these comments, I too am thinking that as long as it functions the 5oclock brass on mag lock back shouldn’t hurt anything. If it functions at 5 it cant really be undergassed can it? Just so long as it is still cycling.

 

[XLR308]

If you have a standard weight buffer I would try that and then retune your gas block.
My personal experience is I have allways had better results running a low mass carrier and buffer with an adjustable gas block.
This of course is for target and hunting rifles, for a defense rifle I would rather be a little overgassed than on the edge for reliability reasons when it gets dirty.

 

[spife7980]

I do not have a standard spring or buffer. I built the lower for a sbr blackout and I read everywhere that an H2 was the way to go for that so I went for the heavy scs when I saw one on sale. I had accumulated some stuff for the upper but changed that up and with the cast aside upper pieces I finished it out to this on the cheap.
Ill take it out tomorrow and adjust the gas back down to throwing at 5 and see if the brass is still getting mangled. I dont much care about "reliability", Im not needing it for anything other than screwing around and feeding my reloading affliction.

 

[XLR308]

You can get false signs of pressure due to timing issues with the gas system. Such as when you still have high chamber pressure holding the case firmly against the the chamber wall and you are sending more gas to the carrier key and it's trying to forcibly remove the case before its had a chance to spring back when your bore pressure drops.

I think you will see a difference with the standard weight buffer, since it will allow you to dial you GB back and should run a little cleaner also.

If your not a loner like me maybe you have some friends that have a standard buffer you could borrow and atleast test it before buying more parts.

 

[lennyo3034]

There are more factors to ejection pattern than just gassing. Ejector and extractor springs can change it too. I would just base it off mag lock back.

 

[spife7980]

So I reset everything to where it just locks back and it ejects about 4:30 and is much less aggressive on the brass now.

That said, it’s still mucking them up somewhat.

Slamming the bcg on a round placed in the chamber comes out fine.
Firing that round replaced in the chamber comes out with an ever so slight sheen in one spot but fine

Slamming the first in from a mag comes out fine.
It also comes out fine like above once fired.

When putting two in the mag the first comes out fine and the second comes out fine when unfired.
When the second from a mag comes out once fired it has the gouges. That continues on for all of the rest from the mag.

So it only messes them up with multiple shots.

Should I file on this extractor or just run the case heads over a stone to knock down brass gouges before sizing them?
I’m conflicted because I also had two cases with primers popped out. Not blown, they look fine, just no longer in the cases. So would that point to ammo that’s just over pressure and thus that is ultimately the source of my brass mistreatment or do semis sometimes just unlock early and the pressure pushes the primer out as it rocks off the bolt face?

 

[XLR308]

You could disassemble the bolt and check if there are any pronounced raised edges from machining at the extractor cut and ejection plunger hole.

I'm guessing this was still running with the can on ?

You didn't mention in the OP but is this a melonite treated barrel ?

 

[spife7980]

Yes, can on.

Salt bath nitride according to cmmg https://www.cmmginc.com/product/barrel-sub-assm-16-1-mt-4140cm-sbn-5-56mm/

 

[XLR308]

If that is the barrel you bought and installed if you don't thoroughly clean the residue from the nitride process from the chamber it can cause issues like your seeing.

When you first started shooting it did the brass come out with a smoked look to it, the reason I ask is the brass you posted looks that way.

 

[spife7980]

Yeah, I just assumed that’s because silencers are dirty.

I’ll give it a through scrubbing.

 

[XLR308]

I used hoppes #9 and a bore brush on a cordless drill on the last one I installed.

Initially I was overly gentle being a new barrel and didn't clean it out good enough and had issues with short stroking, after a more thorough cleaning it went away.

 

[spife7980]

Gave it a normal good cleaning regimen and after that I scrubbed just the chamber with several solvent soaked paper towels as a bore mop until multiple came out clean. Brass is still just as sooty. The first piece is still fine and clean. I think it’s just from the backpressure that the others are all sooty.

Still jacking up the brass though after the first. And I want to blame it being over pressure ammo but why’s the first always alright? Doesn’t seem to be barrel temp related. The first shot loaded on a hot barrel is fine.

 

[XLR308]

You may be right about the ammo, I know primers aren't allways a good indicator but the primer in your pick looks fine.

Have you headspaced the chamber? I'm running out of ideas but maybe we are reaching at nothing.

 

[spife7980]

Yep, spaced well. Passed the go gauge, failed with one piece of scotch tape on the back.

I’m wondering if the violent nature of the auto feeding is forceful enough that the bullets getting loaded automatically are sliding forward enough in the case to seal the chamber a bit and drive pressures up. That’s the only reasoning I can find for it to be fine on the first shot but showing signs only on the subsequent shots.

I’ll take a few to test subjects to measure when I get back home to my tools to measure.

 

[Precision Underground]

I would run some different/LC brass through it and see what it looks like.

 

[spife7980]

I would run some different/LC brass through it and see what it looks like.

This frontier is supposedly a collab with a hornady bullet in lake city brass. That’s why I went for it.
But I intend to pick up a box of Norma tac and a box of federal to test with, will have to be next weekend though.

 

[spife7980]

I measured some of those that got fed in automatically and they measured the same as the unchambered. So my theory of inadequate neck tension letting the bullet jam the lands isn’t the issue. There weren’t any land marks to start with but I can now imperially say that it’s not the problem.

Guess it’s just over pressure. I’ll try other ammos next weekend

 

[RTH1800]

Some Hornady Ammo is hot! Blows primers etc. Hornady does not seem concerned in the least.
They dismiss it as “a custom gun problem.” Even though it blows primers in every rifle I shoot it in.

 

[Foghornleghorn]

I have shot 2 boxes in the black with a new barrel both showed signs of too much pressure with ejector swipes and on a couple extractor cuts. Federal Fusion I shot after them showed neither.

 

[spife7980]

The American eagle 55grs shot just fine with no nasty gouging. Just hornady ammo that’s too hot.