A couple of months ago I built a 6.8SPC for my brother as a promotion gift to GW Major with TPWD. The build is using:

custom billet upper and lower from a now defunct EDC Tactical
Wilson Combat 18" 6.8SPC II Ranger barrel
Strike Industries LPK & UPk
LaRue MBT trigger
PSA 6.8/.224V BCG. Pretty sure it's their "premium" or above average. Most likely made by Tool Craft
Wilson Combat Furniture
Giselle Slim Handguard
ASC 6.8 mags

After the build, I had to beg, steal and borrow ammo from the OB and ammoseek. So we only had about 40 rounds to get it to test fire and broken it. It's a double feeding machine. So I had my brother ship it back to me, and I'm trying to figure out why it's not reliable.

Today I was able to get some ammo, so I decided to load 5 rounds and cycle them to see how it fed. It was flawless and smooth. Then **** went sideways. After about 30 cycles, the ammo started to jam up in the magazine and the magazine quit locking up smoothly. Finally I was only able to load 2 rds at a time because the mag follower quit. But when I went to cycle (yes, a live round) I got sprayed in the face with powder and an empty case ejected. Bullet stuck in chamber.

I used a cleaning rod to dislodge the bullet and then gave the entire chamber, bore and BCG a thorough cleaning. I did notice a decent amount of brass shavings in the residue.

So, what do you think is then cause of my double feeds? I suspect magazine first, but could a gritty chamber (gritty enough to unseat a live round) also be the cause? Or do I have a gas/buffer weight issue I haven't yet worked out because I still haven't fired it.

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What ammo were you shooting?

Ammo
Magazines
Gas system length
Gas port diameter

Report back on these and we can probably come up with a diagnosis.

Ammo was Hornady Black 110g that he shot and got the double feeds, not locking back on last round etc. yesterday I was lot firing the rifle, but simply cycling rounds via charging handle.

ASC 6.8 mags are what we have now. I ordered some C Product 6.8 mags last night

It's a mid length gas system.

Wilson doesn't list the gas port diameter on their website. I'll have to take the gas block off and get back to you.

You just used one magazine for all testing? Any feeding issue troubleshooting should start with trying another magazine.

I'm not a fan of running live ammo "by hand" to test feeding either. You're not going at the speed it will while shooting so it is pretty useless as a diagnostic tool, and slow feeding ARs causes additional super bizarre issues that don't happen at speed and can sometimes royally jack up ammo (as you experienced) which also makes that ammo useless to diagnose anything with in live fire since the now damaged ammo could cause malfunctions too.not to mention the minimal but still real risk of an ND when repeatedly running the same live ammo through a gun with a floating firing pin.

I agree on hand feeding. I'll try to get it on a range this weekend now that I have 100 rds to actually do something with.

Location?
I agree an alternate magazine is the first thing to try.

A bullet jammed in the rifling, with the extra freebore of a 6.8 SPC II, indicates a lot of bullet travel from (repeated) chambering. Maybe check the cartridge OAL after chambering?

I'm in DFW.

Check out the photo. I happened to snap a shot of the mag to show my brother the feeding issue. Notice how far the first round in has pulled out of the case. That's the one that stayed in the chamber. I'm betting I have a magazine issue and the repeated chambering caused the bullets to increase. OAL which gave me the stuck bullet

I hate the ****ing photo filters....... Take them off TEXAGS!!!!!

Sounds like you have multiple issues going on here..

Have you checked the headspace?

You mentioned it doesn't lock open after last round. Is this every time?

What gas block are you running? Standard or adjustable?

What buffer are you running?

It's Gisselle non-adjustable gas block

Buffer is a PSA. Maybe this will help.

Shawn, here's what I know. I never shot the rifle after I finished the build. Usually I'll lube the hell outta a new build and do a few mag dumps to "seat"'all the parts and then give it a good cleaning. With ammo shortage we never were able to do that. I asked him if he knew which way the brass was ejecting and he said "sporadic".

I do recall the gas tube was much harder to mount to the block than usual. Is it possible to have it "off center"?

I've built 6-7 ARs and none have given me this kind of issues. The lower/upper was from a company that has a bad following on AR-15.com. The owner was terrible at CS, but they did do custom logos so I go the TPWD Game Warden Special Operations Logo put on the mag well since that's the group he's now leading. Lots of complaints about poor machining and out of spec tolerances.

Here a photo of a double feed I got from hand cycling. Th is had to be a mag issue.

Unlikely to get a gas tube off center with the block. You can pin it upside down so the port in the tube is not lined up with the port in the block, but if you did that, you would not get the tube into the upper as the bend would be the wrong way.

What is common is misalignment of the port in the barrel and the gas block. Traditionally, the barrel is cut so there's clearance between the shoulder and the gas block. This is not always the case these days. If your gas block has 2 set crews in the bottom, remove the gas tube, remove the set screws, put the block on the barrel rotated 180 degrees. Push it against the shoulder, look through the set screw hole to see if the gas port is centered. If it isn't, pull it out until its centered, place a feeler guage between the block and shoulder. When you reassemble it, maintain that spacing to ensure the block is aligned with the gas port in the barrel.

Feeding issues while hand cycling is common. If its double feeding when fired, swap magazines first and go from there.

That doesn't look like any 6.8 magazine I've ever seen, definitely not an ASC unit....


Added---AR magazine source
https://www.jsesurplus.com/mags.aspx

I've had an 6.8SPC setup for about 15 years or so and magazines have always been the weak link. Go with steel mags from PRI or Barrett. I've also heard the same mentioned by Chris Bartocci somewhere along the way.

That would be my first step.

PRI mags FTW

Sounds like the bolt isn't traveling back far enough to holt open or completely eject or strip the next round.
It's not even going back enough to lock up the bho.
Had this issue with a 9mm. Check buffer buffer length and weight.

GSS said:

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That doesn't look like any 6.8 magazine I've ever seen, definitely not an ASC unit....

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Good call, I hadn't noticed the pics last night. Only polymer mags I know of for 6.8spc are Magpul mags made specifically for LWRC Six8. Unless this lower is a clone of that, the Magpul won't fit in the magwell.