Help with SBR AR functioning

[CTS Tactical]

would recommend an adjustable gas block. round $10 bucks... Did you watch the video?

An adjustable gas block can only restrict the gas available. It cannot increase the amount of gas. If it were over gassed then adjustable block would solve the problem. It cannot solve an under gassed situation.

 

[Propilot]

But how do we know if that is the case the fixed block might just be too restrictive. And if it is under gassed the barrel can always be enlarged.

The gas block is the easy way to adjust the action, as long as the spring rate is acceptable.

 

[GAGunguy]

Get an AK.

Problem solved

 

[CTS Tactical]

But how do we know if that is the case the fixed block might just be too restrictive. And if it is under gassed the barrel can always be enlarged.

The gas block is the easy way to adjust the action, as long as the spring rate is acceptable.

The port in the gas block is generally at least twice the size of the port in the barrel. I have never seen one where the block was restricting the gas and I have seen one or two.

 

[Radar363]

Get an AK.

Problem solved

 

[rumrunner55]

I think it’s your spring/buffer was having this issue with an adjustable gas block and lightest spring fixed the issue

 

[fast306stang]

Does the bolt lock back on an empty mag when you pull the charging handle all the way back?

 

[CTS Tactical]

I think it’s your spring/buffer was having this issue with an adjustable gas block and lightest spring fixed the issue

After reading the OP again, I am inclined to agree or at least say again, try standard carbine buffer and spring and see if that fixes it. Never start a new build with a heavy buffer and spring. Heavy buffers are bandaids to solve over gassed situations. You don't know if you have an over gassed gun or under gassed until you try it with standard components. That very well could be all that is needed.

 

[Ga.Dawg]

Thanks for all the help!! After posting the question I cleaned it and grabbed some factory 220 and some other 220 reloads along with the same mags. Loaded all five mags with one round and test fired and all held the bolt open after fired, I then loaded all mags with 15 rounds and all worked flawlessly and ejected right at 3/3:30 about ten feet out. Pretty sure that I had used some reloads that had been loaded for a bolt gun and handi rifle. Again thanks for all the help!

 

[cmshoot]

While we’re on topic. 11.5” factory sig upper. Unsuppressed, no problem… suppressed it does fine until the last few rounds of the magazine then starts to have FTF. Ejects fine, but won’t pick up next round. Mostly shooting .223 55gr. Pretty sure regular carbine buffer and spring. Haven’t been able to find any info on gas port size except rare report of someone who’s taken it apart and measured it, and IIRC, it was just under 0.063. Sig CS says they’re mil-spec, but there is no mil-spec on 11.5”, but also says they use the same gas port size on all their barrels. So maybe mil-spec M4 @0.0625.

If that is the actual size of the gas port, it’s way too small. 11.5” 5.56 with a carbine length gas system should have a gas port of 0.70”.