Crazy ejection going on...

[Trock03]

Had the opportunity this weekend to workout a new Grendel upper I put together recently. I chose to run with a Seekins adjustable gas block and started shooting with it pretty choked down. Made adjustments till it would lock back reliably.

After that I shot a few 5 round groups. Nothing for accuracy, was just wanting to make sure that it would run reliably. The ejection pattern is very strange. One or two cases will get thrown a few feet away at around the 2 o'clock position and then a few seem to just fall out of the ejection port. There is no set pattern that I can discern. It's completely random. FYI I was shooting factory Hornady SSTs.

I've been around M16s/ARs for 20 years and never run across this. Anyone have any insight into what might be going on?

TC

[tackdriver]

I have had my 24" bull upper run like that . I am not sure what causes it but I also have a adjustable gas block

[stokesrj]

Try opening up your gas port larger, I think you will see the issue go away.
Bob

[Trock03]

Bob,

I've been playing around with that idea. I feel that running an adjustable gas block give you some wiggle room on opening the gas port if you don't have a high-end press/mill. My hangup with that operation is that I'm not real excited to do anything on my own that will affect a change to the bore. I'm very mechanically inclined and some would say I'm marginally intelligent but I'm not an experienced machinist/professional gunsmith.

What does the hoard say? Drill or don't drill?

TC

[explorecaves]

If you do decide to drill it out, get a couple sizes of bits between your current and final size and use a pin vice to hand drill the larger hole.

[montana]

Put a wood dowel down your barrel so you wont hit the opposite side of the gas port hole in your bore. I would make sure you are not over gassed because your brass ejection will do the same as your describing when over gassed. I would try different recoil buffers before I started drilling out your gas port. What weight buffer are you using? Make sure your barrel gas port is lined up with the adjustable gas block port hole. Measure from the front of your adjustable gas block to the inside hole, and then measure the distance between your barrel shoulder and gas port hole. Don't just slide your adjustable gas block up to the barrel shoulder and think they will match. Gas blocks vary between manufacturers. Drilling would be my last option.

[cst]

don't drill anything..just open up the gas block a couple clicks
..maybe you have it just too perfect that when the factory ammo fires....some maybe running a little hotter than the next few rounds which could have some difficulty ejecting. the only way to be sure is run it through a chrono and see a pattern and try shooting it wide open.... then go with a light buffer, spring, ..etc...

[Drifter]

One or two cases will get thrown a few feet away at around the 2 o'clock position and then a few seem to just fall out of the ejection port.

With brass falling out of the port and / or being thrown forward, it seems potentially overgassed to me. I would lean towards turning the gas down.

With an adjustable gas block, it should be easy to test, especially before taking other more drastic measures.

[Trock03]

Thanks to all for the input. I'm going to spend some more time on the trigger before I start removing metal. Just FYI the barrel is 18" mid-length paired up with an A2 stock and standard rifle buffer. Tried both a mil-spec rifle spring and then a stronger Wolf spring. No difference in performance between the two.

Out of curiosity, is there a standard diameter for the gas port on an 18" middy Grendel? Also, could this be an ejector spring issue?

TC

[explorecaves]

I know the gas ports have been posted before.... I can't find them off hand though. Probably be a good idea to get that info stickied.

Edit, found it:
22" RLGS: .094"
20" RLGS: .094"
18" RLGS: .096????? or a little larger
16" MLGS: .078"

[Shivesy]

These are my port sizes on my barrels.
#1) 20" Barrel Rifle Length Gas Systen. (.093)
#2) 16" Barrel Mid Length Gas System. (.078)
#3) 16" Barrel Carbine Gas System. (.062)

I have drilled them myself using the wood dowel rod method. If that's what you decide to do, don't be afraid as drilling is very simple.