6 Inch Build Giving Me Fits

[shortround60]

Good Day All.

I have been a member of this forum for a while and try to soak up as much as I can. I'm greatly appreciative of the information shared here and could definitely use some guidance to solve an issue that I am having with my 6 inch build.

6 in Ballistic Advantage Barrel
Adjustable gas block
Franklin Armory Binary Trigger
Light Weight BCG
Ultra Light Weight Buffer & Springs
SB PDW Brace

I primarily intend to use this suppressed, but want it to function without the can as well. My can is a GMT-300BLK that I have had for years. The pistol cycled flawlessly prior to me switching to an adjustable gas block to achieve lock back on an empty mag. Once I changed, it cycled unsuppressed, then produced hickups when suppressed.

Does anyone have any suggestions regarding where I could start to tune this thing? Thank you in advance for your input and I will not take offense to jabs, ribbing, etc.

Shortround60

[dellet]

Rule of thumb is if it cycles subs correctly and has problems with supers, you’re over gassed.

Switching to an adjustable block to achieve lockback suggests you were under gassed, or at least thought so. It actually might have been over gassed the whole time. I would just start closing off the gas and see what happens.

If this is using pistol gas, you probably will not be able to have one setting to work both suppressed and not. There is just not enough dwell time. You might even need 4 settings, sub/super/suppressed/not. It will depend on the loads.

Knowing load data would be helpful.

[shortround60]

Thank you sir.

I will try closing off the gas.

My pet load is 200gr projectiles over 11.4gr of CFE Black. I have thought of experimenting with H110/Win296, A1680, Lil Gun and IMR 4227, but prefer to stick with 200gr projectiles primarily.

If I must decide how to use this build instead of using multiple settings, I may lean toward this particular pistol being used for a PDW and using only 110gr loads.

I have several other 300blk builds and this one started a "toy" of sorts.

Thank you once again for the suggestion and I will post how closing off the gas works out. I am always willing to learn, so please keep the information coming.

[FightingSquirrel]

Another thing that you might want to verify is that you have placed the gas block correctly. My rookie mistake the first time was not having the gas block set off of the shoulder .025. I shot supers great because the gas block was wide open. Switching to subs the gun wouldn’t cycle good. I have come to appreciate an adjustable gas block, but if not installed correctly it can mask a lot of issues.

FightingSquirrel

[shortround60]

Thank you for the suggestion. I will double check that as well this weekend.

[shortround60]

Fighting Squirrel, I checked and the gas block is set properly.

Dellet, I closed off the gas port and then fired factory 200gr subsonic ammo (Sellior & Bellot) and got it to eject the spent casings. It didn't strip the next round from the magazine or lock back on a now empty magazine.

In your opinion, what should be my next move based on it probably remaining over gassed. I was thinking if I switched back to a regular BCG versus a light weight one, it may slow it down. I could also go back to heavier springs/buffers. I have heard JP Silent Capture buffers help. I like the size of this build and would love to get the kinks worked out.

Thank you all once again for your input and suggestions.

[FightingSquirrel]

My guess is your bolt is traveling way to fast. If you have a mil spec BCG put that in And see if it cycles. Light weight and ultra light weight BCG’s really mess up the timing. If it works with the mil spec, then just settle in for trial and error until you get it to run. In my opinion, nothing at all is gained with a light weight BCG. The rifle is designed to function at a specific bolt velocity. Increasing lock time really serves no purpose.

[dellet]

Fighting Squirrel, I checked and the gas block is set properly.

Dellet, I closed off the gas port and then fired factory 200gr subsonic ammo (Sellior & Bellot) and got it to eject the spent casings. It didn't strip the next round from the magazine or lock back on a now empty magazine.

In your opinion, what should be my next move based on it probably remaining over gassed. I was thinking if I switched back to a regular BCG versus a light weight one, it may slow it down. I could also go back to heavier springs/buffers. I have heard JP Silent Capture buffers help. I like the size of this build and would love to get the kinks worked out.

Thank you all once again for your input and suggestions.

First thing to do is set a benchmark. If I was to buy ammo off the shelf and expect it to work, it probably would not be the S&B. Maybe Remington UMC, it has a reputation for being loud, not so accurate and tends to go super in a 16” barrel, but it cycles and locks back everything.

You say you closed the gas port, how far?

First time working with an adjustable, I would close it completely. The carrier should not move. Open it a couple clicks at a time until it locks back, then open it one more click for reliability.

Also just wanting to be clear on what I think you said. Basically it worked better without the suppressor attached, cycled fine just did not lock back on empty.

Changed gas blocks and cycled without the suppressor, added the the suppressor and it would not cycle.

All with the same load.

If you changed loads in there somewhere, it will probably change my thinking.

[shortround60]

Dellet, All of the performance from May 30th was with the factory S&B ammo.

I closed it off and started with one rotation. It did not move the carrier. It moved the carrier at three, but stovepiped the spent casing. At four it threw the casing, but not lock back.

My previous experience with a non-adjustable gas block was with my CFE 11.4gr loads. I wrongly assumed that factory ammo would be better and that is when I started using the S&B since it performed well in my 10.5 build.

I do have some Remington 220 in my stash and may start doing the remaining tests with that as you suggested. I will update once I test it again.

Thank you once again for all your feedback.

Shortround60

[shortround60]

After a couple of weeks of not being able to make it to the range, I finally got a chance.

Dellet, I switched over to Remington 220gr OTM and sure enough, it cycled flawlessly.I still didn't get it to lock back on an empty mag, but not a single stove pipe.

I really need to find out what powder Remington uses. Thank you all for your advice on this and I will hopefully get this tuned to lock back on an empty magazine.