First AR pistol build - Help Request

[Dibs50]

While I've owned AR's for years, this is my first pistol build. During function testing, I had FTE/FTF issues. I've searched this site and suspect that it's an over - gassing problem. I've attached some photos and hope someone could assist me.
My build took some time as I gathered the parts as I could afford them. Here are some details :
10.5" BA performance barrel
Tactical Machining upper
ALG 10" EMR V-3 handguard
Carbine length gas tube
Non-adjustable gas block
KAK Industry Flash Can
Anderson BCG
AERO Precision lower
Carbine buffer (2.9oz) and spring

I'm shooting handloads
147gr M80 pull downs over 17gr of Lil Gun. COAL: 2.145

Problem: I'm getting both a FTE and a FTF. Cycling one at a time, the BCG locks back on an empty mag. It has worked with 2 & 3 rounds in a mag. More than that and I start having problems. I've tried both 20 & 30 rounders, Military and civilian (Magpul) magazines. I don't see any signs of pressure. Should I be looking to get an adjustable gas block? Any help would be greatly appreciated.

[alamo5000]

I would most definitely start with an H2 or H3 buffer. An extra power buffer spring would help too.

It's common with SBR/pistols to have a carrier speed that is too fast.

From all appearances it looks like your BCG is getting slammed to the rear and is being driven home too fast.

[Dibs50]

I'm hoping to use this for deer with 125gr projectiles. However, I really hope to get a can some day and shoot 220gr projectiles subsonic.

Would an adjustable gas block be a better (albeit more expensive) option?

[dellet]

Is that two live rounds jammed or a fired and a live?

Having the problem with only more than three rounds, is a feeding issue. It could be as simple as the rounds toeing in too much. This can be exaggerated if there is too much recoil. You might be able to load up a magazine, bang it on your hand and see the tips of the bullets get crossed up.

Cheapest try, would be to back off the load a half or even full grain. No money out of pocket, just time. Lil’gun starts getting a bit unpredictable at the top end of the load, and you’re close.

If you’re going to shoot suppressed an adjustable would be a wise choice for that setup.

For what it’s worth, I load a lot off bullets to max length and charge weights. I use Lancer magazines, and do not use Lil’gun.

10.5” carbine length barrels should come with a disclaimer or buffer/lower specs. It’s hard to get subs to work and supers are overgassed due to most port sizes they are sold with. Add a suppressor and it just gets worse. To give an idea, when shooting supers suppressed, I have the gas restricted about 75%.

Way too many people only heard that you can’t over gas a carbine system. The actual company line from AAC was you can’t over gas a properly ported carbine system.

[alamo5000]

I'm hoping to use this for deer with 125gr projectiles. However, I really hope to get a can some day and shoot 220gr projectiles subsonic.

Would an adjustable gas block be a better (albeit more expensive) option?

You can do an adjustable block. It most certainly won't hurt anything, especially once you add a suppressor into the mix. But for me, I would start with the heavier buffer and a extra power spring.

AFTER you see how it operates with those new items, then add a block if you want to.

[popper]

You did file the ribs in the Pmags? They get jammed for a loaded mag.

[cdl]

I would most definitely start with an H2 or H3 buffer. An extra power buffer spring would help too.

It's common with SBR/pistols to have a carrier speed that is too fast.

From all appearances it looks like your BCG is getting slammed to the rear and is being driven home too fast.

This probably ^^^

I haven't seen that jamb in 300 Blk, but I've seen that in a 308 AR10 where the bullet was jamming the rifling because the chamber throat wasn't cut. I'd add blown primers as an additional symptom. You might want to cast the chamber if you can't see in there.

[nksmfamjp]

If that is an empty on top of a live round, you have a bolt over base failure....

Therefore, it is most likely not enough gas as the bolt did not go back far enough to eject. Does it eject and feed hand cycling?

Now, why are you short on gas? Port size or location? Alignment? ....or is it at the back end?

Also, same thing with factory ammo?

[kilibreaux]

The gun isn't clearing the fired case before picking up the new round. That means weak ejection, but not likely "undergassed" since a pistol length system puts plenty of gas into the system, unless the port is too small. A bolt that locks back on a single round fired, or works with three rounds but starts to act up on more means stack friction is overcoming bolt throw. The primers appear well flattened indicating adequate pressure, as evidenced also by the striations showing on the fired case jammed in the action, but clearly, the fact that two cases are present - one empty and one full, means the action failed to clear one before attempting to chamber the other.
You might need to experiment with a faster powder that moves your peak pressure curve closer to the port, or you can do as so many of us have and mount a Krinkov "brake" which is really a muzzle "booster" that increases back pressure and makes short barrel systems work. If you do go the Krink route, first, don't buy some other, high-dollar brand, stay with the "cheap" Krink, then shorten the straight tube section behind the cone-shaped funnel to gain clearance between bore exit and gas chamber. The Krinkov style "brake" was designed to make short-barrel AK's function and it will do the same with an 8 - 10" AR "pistol."
With the Krink "brake" you can then give some consideration to a heavier buffer so slow your cycling mass.

[kilibreaux]

Remember that 300 Blackout produces high pressure with low volume so your port pressure becomes more problematic. Examine a powder burn rate comparison chart and consider trying powders faster than you are using, or go with heavier bullets, or go with lighter bullets in the 110-125 grain range and go for velocity which means powder choices and charges that will cycle the pistol system without a hitch.