Hey folks so finally got up to the range to shoot my new carbine. Had some issues, one of the guys here today was helpful but the problem persisted.

First issue.
Bolt failed to opperate after the first round.
Took the ff grip off and the gas block was loose ( two set screws). So we tightened that up and then fired again.

Second issue.
Once gas block was tightened set against the cut out of the barrel when i charged the rifle i would get a light hammer strike eg no boom. Once we moved the block forward a but like 1/8" i was getting a fail to extract as well as a double feed. Supsected it was over gassed?
We moved the gasblock incrementally to narrow down the port a bit. I also swapped my colt bolt into the bcg to see if that made a difference. It started to work and the 2mags I put through out were ejecting around 4oclock or so almost the same as the Colt.

Tried another shooters pmag with some steel case ammo
And then the problem of not extracting and the double feed happened again.

Also it seemed that the rounds were catching on the groove on the feed ramps. A lot of copper buildup there.

The bolt I swapped out worked just fine in the Colt. I'm lost right now. Any suggestions? I hope I'm describing the situation properly.


Specs are:
10.5" S&J barrel
S&J m16 bcg
Nea low profile gas block (I believe) it cant butt up against the cutout on the barrel see above.
Carbine gas tube
Winchester 55g fmjbt .223

Help please lol. I can take pictures or describe things better if need be later tonight.
Cheers

was bcg properly lubricated?

Does the bolt lock back on last round?

Is the gas block properly lined up?

Ejection pattern?

Yes the bcg was well lubed.   The gas block was lined up.   Just when in the full position it seemed like it was super over gassed.  This was my first time taking out out on the range since assembling it.  As I said above the 2 mags (rounds or so that it operated properly my brass was landing aprox 4oclock  or so.   The same as my Colt. And the 2 mags did lock back after the last round.  Until it stated messing up again

What buffer/spring are you running? Wondering if that may be a possibility...

Im running a kac SR15 buffer

Its a gas issue and if the gas block came loose then look at replacing with a pinned version. I would also check the gas port to make sure it is spec correctly and there is no blockage.   As for an SBR look at using a H3 buffer with mil spec carbine spring. Look at carrier group for proper gas rings and gas key is secure. Use quality mags, ammo and make sure weapon is properly lubed.

Thanks Lil commando.   The heavier buffer was one of our first thoughts.  Nobody at the range was running anything but standard buffers. Is it possible to go too heavy there?  

Will a pinned gb make that much of a difference?

The bcg gas key is secure and staked.

I have not checked head space with gauges.  Would this create any additional issues?

Check gas port or have a qualified person do so to verify no blockage and correct size.  A pinned gas block is more secure then the one you have that is why many people take there standard FSB and shave it for a low profile and pin it back. I run a Colt 6933 but it worked fine with the H buffer it came with but I switched to H3 to minimize the violent action/movement and to also help save wear and tear on the system.  Use good ammo and not any low power stuff which could help if no gas issues are found.  Many barrels have the mil spec port size which can have an issue with low power ammo.  Just think about the cycle of operation and use this to help find where the problem is or could be.

If the chamber is not 5.56 and this is what your shooting then eventually you could have extraction issues.  But first start at the basic and find an H2 or H3 buffer and make sure your gas system is working properly.  Since your gas block came loose then make sure you check there and verify if its the right size for your gas port.  I'm in no way an expert and it is difficult to figure out the issue without the weapon in front of us.  I am a Colt Armorer but there is always something to learn.  A friend had an issue similar to yours and it was the gas port sizing.  It was to small and had to be opened up.

Great info I appreciate all the wisdom and experience on the forum.
Is it possible that the gas port on the barrel is too large?
I'm going to keep am eye out for a pinned gb or may go the route of grinding down a fsb to try that.

I guess I have to ask will all this help with the fact that it was not extracting the round from the chamber? Though if I cycled the action manually it would.   Secondly is it normal to get heavy buildup up copper on the feed ramps.  My only other experience with this platform is my Colt and I don't see that nearly as bad as on this one.

I agree, it sounds like over gassing.

My 7.5" upper was doing the same thing

Rather than messing with a bunch of spring and buffer combo's and maybe fixing it, I'd look at just putting an adjustable gas block on it.



ETA- What's your deflector look like?

There was some noticeable brass marks from when I got the 2 mags to function (the only time it cycled properly) and it was landing at around 4 oclock.   I'm going to strip it down again tonight and see how things look.  

I think finding am adjustable gas block may be slightly harder up here in Canada?

I don't think they are an ITAR item.

You can even order them off Amazon.

Any recommendations on brand etc?  I'm new to this and none of my buddies have any experience with them.

Will a heavier buffer help as well or should I start with the adjustable gas block