I need your advise to trouble shoot my new build please

[JimIllinois]

Hello,
I am new to the group and hope someone out there can help me with my problem.
My build has an Anderson A3 upper, Aim NIB BCG, Faxon 7.5" socom barrel with a faxon gas block and pistol length gas tube and a Phase 5 buffer assembly.
1st trip to the range this weekend and it will load the first round when using the charging handle , it fires, the trigger resets, the round ejects but it wont load the next round and the bcg stops about 2/3rds closed. The rounds were 110gr and 150gr both loaded to spec and I tested them in my basic Daytona tactical 16" barreled rifle and both rounds run flawlessly.
Can someone please give me a starting point on what to try first, ive read that it could be a gas issue or buffer issue I'm hoping you can pin it down more for a starting point
thanks

[Sithlord]

Hello,
I am new to the group and hope someone out there can help me with my problem.
My build has an Anderson A3 upper, Aim NIB BCG, Faxon 7.5" socom barrel with a faxon gas block and pistol length gas tube and a Phase 5 buffer assembly.
1st trip to the range this weekend and it will load the first round when using the charging handle , it fires, the trigger resets, the round ejects but it wont load the next round and the bcg stops about 2/3rds closed. The rounds were 110gr and 150gr both loaded to spec and I tested them in my basic Daytona tactical 16" barreled rifle and both rounds run flawlessly.
Can someone please give me a starting point on what to try first, ive read that it could be a gas issue or buffer issue I'm hoping you can pin it down more for a starting point
thanks

Certainly sounds under gassed. Triple check that the gas block is DIRECTLY over the gas port. Measure the gas port as well. With a 7.5" barrel and pistol length gas tube, the dwell time (amount of time from when the bullet passes the gas block to when it exits the barrel) is short. This is the only time that gas is used to cycle the action. On your 16" barrel, the dwell time is much greater. To accommodate the shorter dwell time, you generally either make the gas port bigger, and/or go with a lighter buffer.

Sounds like you built an AR pistol. With normal pistols, having a weak-ish grip can affect recoil (to the point of having misfeeds). I wonder if, you, the shooter, might be absorbing some of the recoil. You said 'loaded to spec' which also implies reloads. Start with factory ammo, and see how that reacts. If handloads, the choice of powder may be the culprit.

[threehundred]

If this was my problem, first thing I would do is cycle an entire mag BY HAND.
If no problem cycling an entire full mag by hand, with vigorous lock-up, I would start
investigating the entire gas system.

If it doesn't cycle an entire mag by hand, with vigor, I would hand cycle it without a MAG.
If no problem cycling by hand without a mag, reinsert a full mag and hand cycle until it
either locks up with vigor, or you find wear / scratches / contact marks on the BCG. Obviously such wear marks will lead to a solution.

If all these procedures pass with flying colors I would begin investigating the chamber mouth/feed ramps etc.. You say, only "2/3rds closed", but, even if the gas system is underpressured, your buffer spring should be cycling a round unless there is a chamber problem.

If it cycles by hand correctly, if the gas system checks out, if the chamber doesn't need some polishing, I would then begin intense measurements verifying compatibility of ammo dimensions to chamber dimensions. But, my guess is, you will find the culprit before this stage.


JMHO, since I am not a professional armorer.

All the bests to you!

[Jim Timber]

You might need more lube.

You should be able to hand cycle the bolt carrier to not pick up another round (short stroke) and still have it ride over a full mag to complete lock-up into battery on an empty chamber. This gets iffy when the gun is dry. NiB is nice because it cleans up easy, but people who claim you can run it dry are idiots. Your gas rings need lube, and your receiver needs lube, the cam key needs lube too.

Everything should be wet. The biggest function issues I've had on new builds were when I didn't have enough oil on the recoil spring and it dragged on the receiver extension enough to fail to push the carrier into fully locking the bolt.

[Ghmann]

Could just need some more break in. How smooth is the BCG when you rack the charging handle? Any binding? Make sure the BCG is well lubed. Try a different magazine. Check the gas block and insure it is aligned properly.

[JimIllinois]

Thank You everyone, all great advice and I will start with breaking it down to see if I can find an issue before I can get to the range next week and try your suggestions on firing as well

[shadepuppy]

as a last resort.....I'm wondering .......the phase 5 "lays" on your cheek and your 16" anchors to your shoulder......I wonder if you are experiencing what we call "limp wristing"
on a hand gun

[Boolit_Head]

Some gas blocks are designed to sit about .025 off the shoulder of the barrel. That is to allow for the mounting plate for the 2 piece hand guards. When they are flat against the shoulder of the barrel the hole is not aligned. If it is a set screw type take out the back set screw and flip it over and align the hole with the barrel. That will give you the dimension to space it off the shoulder. The set screw is usually directly under the gas hole. If those two gas holes are not aligned you are not getting enough gas to cycle the action.

[Gunzer]

Like others have mentioned, definitely verify your alignment between gas port and gas block. It's easy to assume that your gas block should rest against the shoulder of your barrel. Had I assumed this with my build, the alignment would have been off by a considerable amount.

[GSO]

You might need more lube.

You should be able to hand cycle the bolt carrier to not pick up another round (short stroke) and still have it ride over a full mag to complete lock-up into battery on an empty chamber. This gets iffy when the gun is dry. NiB is nice because it cleans up easy, but people who claim you can run it dry are idiots. Your gas rings need lube, and your receiver needs lube, the cam key needs lube too.

Everything should be wet. The biggest function issues I've had on new builds were when I didn't have enough oil on the recoil spring and it dragged on the receiver extension enough to fail to push the carrier into fully locking the bolt.

This is where I would start as well. Synthetic motor oil works really well.