Build Thread Gas issues on a new build

[Roymil666]

So over the past few years I've built around a dozen black guns with pretty good success. But a current build has me scratching my head.

The issue I'm having is failure to feed. Will eject a round but not cycle a new one. Tried multiple mags and 55 and 62gr. Running a BA Performance Series 16" mid length 223 wylde barrel with pinned gas block (I double checked the gas port for orientation). WMD nitride gas tube. SAA NiB M16 BCG. Armaspec H2 Stealth Spring.

I swapped to a spare Carbine Buffer and Spring I had lying around and that seems to help the issue. (failure 1 out of 10rnds). I've never had an issue with a fully gassed mid length running an H2. The only part I've never used before is the NiB BCG, but I don't see how that could be the culprit (I checked that the gas key was torqued and staked).

What are your ideas on this one? Undergassing? Bcg issue?

Read More

 

[titsonritz]

With one round in the mag, will firing it lock the bolt back?

Sounds like you have more than one AR, have you tried a differant BCG?

 

[titsonritz]

The only part I've never used before is the NiB BCG, but I don't see how that could be the culprit (I checked that the gas key was torqued and staked).

I've seen them cause tons of issue and may very well be your issue, hence my above suggestion. Bolt Material: 9310 Nitride Treated is an automatic disqualifier for me.

 

[Roymil666]

It does lock back and ejects a good distance. I'll have to try swapping the bcg as soon as my buddy gets back from camping with it. Had to have it.

 

[Cerberus Group]

Having gas issues, if it is gas issues can have multiple points of failure.

The obvious;

Gas block alignment, barrel gas tube port wrong size,, gas key screws tight and staked properly

Not so obvious;

Gas tube out of spec, gas block out of spec, gas key out of spec, BCG out of spec in 1 or more multiple areas.

People treat the above as drop-in parts, but one should spec everything before assembly.

Then there's the action spring and buffer. Stick to an original design buffer and spring, and you'll go far with your trouble shooting.

 

[titsonritz]

It does lock back and ejects a good distance.

Then it shouldn't be a gas issue.

My money is on the BCG and/or that buffer assembly or worse case out of spec chamber. I, too, would recommend sticking standard buffer system. Everything should be able to run an H buffer with half way decent ammo. I also would recommend using quailty factory ammo, no reloads, for doing diagnostics.

 

[ELRShooter]

This helped me fix mine.

 

[Roymil666]

I'll try to single it out an issue at a time. I tried federal 62gr and pmc 55gr for the little troubleshooting I was able to get done. I use jp silent springs in all my personal builds and have used these armaspec buffers in other builds and haven't had any issues until now.

I actually bought two bcgs for this build just in case one didn't arrive in time. Of course the nitride 158 car one is the one that didn't show up in time before his trip.

 

[DirectDrive]

The issue I'm having is failure to feed. Will eject a round but not cycle a new one.

So this failure to feed....describe it.
Does the BCG ride up and over the top round in the mag ?
Does the BCG push it out of the mag but it gets hung up on the way to the chamber ?

The one weird clue is "carbine buffer and spring seems to help".
That tells me that this combo may be getting you more rearward travel.
Which tells me that your original buffer and spring were not traveling rearward enough to pick up a round.

Also "BCG locks back when one round is fired".
An interesting exercise (with clear firearm) would be to lock the bolt back.
We know that the bolt goes back that far when fired.
Then insert a mag with a round (or a few rounds) in it.

Does it look like the top round will get picked up ?
Keeping the muzzle pointed in a safe direction, let the bolt fly from the locked position and observe what happens.

Do try a known, good BCG.
If that doesn't do it, then there may be something wrong with the way the top round "presents".

 

[TTSX]

I've seen them cause tons of issue and may very well be your issue, hence my above suggestion. Bolt Material: 9310 Nitride Treated is an automatic disqualifier for me.

Nothing wrong with a good ol full mass phosphate BCG and 158 bolt.

 

[TTSX]

This helped me fix mine.

View attachment 976183

My most recent build ejects between 230 and 330 and I was getting super annoyed about that. When changing buffers, the only thing that changed was recoil impulse so eff it. Decided good enough but it still bugs me. Granted, the average is probably about 315 so it's good. But grrrr.

 

[Roymil666]

There was a difference in "buffer" weight from the captured Spring (h2) and standard (carbine). I'm thinking it's undergassing for some reason and not cycling far enough back to pick up a round. Now that I'm thinking about it; it may not have locked back every time.

 

[TTSX]

I'm gonna ask, since it hasn't clearly been stated, are you using good, brass cased, factory 5.56? I have more than one that will do as you described with steel .223 so I just run them with the "good stuff" and use the "cheap stuff" on my carbine gas system rifles. Can't say why I thought those were a good idea.

Edit: I see now where you said federal and pmc. Still worth thinking about

 

[Roymil666]

One of my posts above I stated I ran 55gr pmc bronze and Federal 62gr.

 

[TTSX]

One of my posts above I stated I ran 55gr pmc bronze and Federal 62gr.

I read that after my question. I must have glazed over it. Ah well. Can't win em all!

 

[titsonritz]

One of my posts above I stated I ran 55gr pmc bronze and Federal 62gr.

PMC Bronze is underpowered ammo.

 

[titsonritz]

There was a difference in "buffer" weight from the captured Spring (h2) and standard (carbine). I'm thinking it's undergassing for some reason and not cycling far enough back to pick up a round. Now that I'm thinking about it; it may not have locked back every time.

If it is locking back it should not have a problem picking up the next round. I thought you were saying it would fire, cycle and eject the round but would not feed a new one. So is stripping a new round from the mag and failing to chamber or not stripping a new round at all?

 

[TTSX]

There's also an option to try the lower with a different upper and the upper with a different lower. Eliminate as many parts as you can all at once.

 

[titsonritz]

This is the cycle of operation...

Feed
Chamber
Lock
Fire
Unlock
Extract
Eject
Cock

It then repeats.

Exactly what is it not doing from that list?

 

[titsonritz]

There was a difference in "buffer" weight from the captured Spring (h2) and standard (carbine). I'm thinking it's undergassing for some reason and not cycling far enough back to pick up a round. Now that I'm thinking about it; it may not have locked back every time.

This is why I pin gauge everything I build. If you want take off your handguard and gas block I can measure it, I drive through Aurora a couple times a month going between OC and Salem/Albany. PM me if you want to set something up.

FYI a good range of port size for a 14.5"/16" mid-length gas system would be .076-.0785.