Issues with new build...

[gunner1]

Finally got around to shooting my 6.5 Grendel today. It's built with an Aero Precision upper/lower, Aero Precision 6.5 Grendel bolt carrier group, and an 18" Ballistic Advantage barrel with a rifle length gas system and an SLR adjustable gas block. I'm using a Hogue adjustable stock kit.
The issues were that whether single loading the rounds at first or putting a couple of rounds in the five round ASC mag and shooting, almost every round stove piped. The ones that didn't seemed to be ejected weakly to about the three o'clock position. Also, at no time did the bolt lock back whether single feeding or putting multiple rounds in the mag. The bolt WILL lock back when I pull the charging handle back.
Now, I admit it's been awhile since I've had any issues with any AR and I've owned several in 5.56 and .308 and I've heard that the Grendel presents problems of it's own. I DID try adding more gas to the system but it seemed to make things worse. In fact, after firing a round I picked it up to look at it and believe it or not the brass almost felt cold! Never experienced that before. I returned the gas system to seven turns out from closed.
Any tips or advice would be greatly appreciated!

[Kswhitetails]

From your description, it sounds under gassed. Check gas system. Block, key, tube seals. Alignment. Gas port size consistent with barrel length and loading?

Answer these Qs and then move to the magazine.

I’m about 98% sure you’re under gassed.

The remaining 2% are related to a weak ejector spring, and magazine being new and needing a break in.

One point here, load the mag up and leave it so until you shoot again. It’ll help wear the spring in.

[Drillboss]

What he said.

I've built a half dozen Grendels, 20", 16", and 12.7". The gas system ran fine on all of them, except when my gas block wasn't aligned correctly. Work with your gas system until the bolt locks back after firing a single round. I don't know the details about your specific barrel, but it is possible that the gas port could be undersized. It seems like I remember hearing once that BA undersized their ports, assuming that they would be used with a suppressor.

[wideglidejoe]

I built a 6.5 Gr pistol using a 12.5" BA barrel, I had similar problems. I was considering experimenting with different buffers/springs, etc. I called BA, they told me the gas port size for my barrel (which I thought was extremely small). I drilled it out, it runs perfect now, so I was under-gassed. I'm out of state right now, I don't have my notes, or the drill bit I used with me, so I hesitate to quote the bit size.

I actually started a thread on here about my build, asking for advice. I got several good suggestions, including drilling the gas port larger, which obviously worked. Due to being out of circulation for a while due to a surgical procedure that had a prolonged recovery, then going back to working out of state, I don't think I ever updated my original thread, but my 6.5 Gr 12.5" pistol runs really good now, and it travels with me.

[BCHunter]

BA grendel barrels generally have smaller gas ports, then other manufactures. The 16" Hanson profile barrel I did had intermitant cycling issues, would feed the mag but not lock back last round. I was able to resolve it by polishing bcg and inside of upper. And a few more rounds of break in. My next step would of been drilling out gas port, believe mine was around .680"

[Gusmeister]

Gunner.... since you are not new to builds here is my suggestion. If your adjustable gas block was able to make the problem worse I suggest you take it off and put a non adjustable one on and retest. Nothing against adjustable gas blocks but they do enter a nearly endless list of variables in the balanced DI AR system.

I know a couple guys who had either poorly drilled gas ports or under sized gas ports on their AR's. Problem is you can't get that metal back after you drill it out (though it may be the problem). Non adjustable gas blocks are cheap and easy to test with.

[-Justin-]

What buffer are you running? Does the bolt lock open on last round? Could be over gassed, turn down gas until it won't eject, then start turning back up until bolt locks back.

[LRRPF52]

18" Ballistic Advantage barrel with a rifle length gas system and an SLR adjustable gas block.

What ammunition?

You shouldn't need to choke off an 18" RLGS in 6.5 Grendel, as there isn't much plug dwell with the larger bore volume of a 6.5mm.

With that set-up, you generally need all the gas you can get, especially when shooting lighter weight projectiles and factory loads with anything 100gr or less.

I would start with the gas fully open and also make sure you have a tight gas seal with the gas block to the barrel journal, which most DIY builds do not have.

[gunner1]

What ammunition?

You shouldn't need to choke off an 18" RLGS in 6.5 Grendel, as there isn't much plug dwell with the larger bore volume of a 6.5mm.

With that set-up, you generally need all the gas you can get, especially when shooting lighter weight projectiles and factory loads with anything 100gr or less.

I would start with the gas fully open and also make sure you have a tight gas seal with the gas block to the barrel journal, which most DIY builds do not have.

You know, it's a funny thing but a guy with the EXACT same name gave me this same advice over at www.ar15.com and he turned out to be 100% correct. Great minds must think alike, huh? LMAO! In all seriousness, thanks again for all your help. I really do appreciate it.

[Popeye212]

That dude gets around I saw him over there too!