Proper gassing for 16" middy?

Trumpet · Apr 15, 2014

So I'm contemplating a 16" LW middy. Clandestine told me that if they're gassed correctly, they're fantastic. I tried PM, but it no workie so I thought I'd ask the general population here. What is the proper gassing for a 16" Middy? These are drilled at .081"

BradMacc82 · Apr 15, 2014

I'd have to pull mine apart to spec out the gas port, but it's a BCM barrel, and it runs fantastic with a standard carbine buffer/spring.

kfrede86 · Apr 15, 2014

All I have are mid length and they run flawlessly. BCM as well.

RAC · Apr 15, 2014

I run ST-T2 buffer in my BCM 16" middy. Never had a problem w/ steel case or .223 . H buffer for my 14.5" middy.

ETA - I use CS springs from brownells.

boatbod · Apr 15, 2014

Before worrying about hole size you need to make sure the gas block is positioned correctly (not partially obscuring the hole) and that the carrier is fully engaging the gas tube.

Load one round in a magazine and shoot it, then repeat a few times. If the bolt locks back reliably you are in the ballpark. If it short strokes you can try a lighter buffer or if that doesn't help, a bigger gas port.

Burrs/reamer rings in the chamber can also cause ejection problems, but these can typically be seen by the marks left behind on fired cases.

armed ferret · Apr 15, 2014

bolt locks back and everything cycles fine on that BHW 16" middy we were chatting about. it does eject to about 2:45-3:00 though, not backward at all.

that may be a result of the fact I'm using handloads and probably at least .5 grains (if not more) below pressure signs yet, though.

but yeah, it cycles perfectly and locks back every time.

bmorewineguy · Apr 15, 2014

I'm having the same problem with my mid length build, cycling fine and locking back on last round as well. It's ejecting consistently at about 1 - 1:30. I decided to try swapping the buffer for a heavy buffer because I was thinking it might be overgassed. I just haven't gotten a chance to take it out yet. If that doesn't work out I was going to change out the buffer spring for a heavier one.

Do you all think these could be caused by an weak ejector spring or something else wrong with the ejector?

7A38 · Apr 15, 2014

Trumpet said:
So I'm contemplating a 16" LW middy. Clandestine told me that if they're gassed correctly, they're fantastic. I tried PM, but it no workie so I thought I'd ask the general population here. What is the proper gassing for a 16" Middy? These are drilled at .081"

In my opinion:

If it's 0.750 barrel diameter at the gas port, that port is probably a little on the large side, but OK. You probably want about a 0.078 gas port size.

If the "LW" means it is a light weight 0.625 barrel diameter at the gas port, I think that port is definitely on the large side. You generally/theoretically want a smaller gas port for a thinner barrel.

That being said, I'd rather have a gas port a little too big, than too small. It's easier to compensate for a gas port that is too large.

7A38

dev · Apr 16, 2014

bmorewineguy said:
I'm having the same problem with my mid length build, cycling fine and locking back on last round as well. It's ejecting consistently at about 1 - 1:30. I decided to try swapping the buffer for a heavy buffer because I was thinking it might be overgassed. I just haven't gotten a chance to take it out yet. If that doesn't work out I was going to change out the buffer spring for a heavier one.

Do you all think these could be caused by an weak ejector spring or something else wrong with the ejector?

I had a similar issue with my mid length spikes upper. I too thought it was over gassed based on the ejection of the brass being thrown forward. I corrected it by using a heavy buffer and now my brass is ejected at the 4:00 position which some say is ideal.

I later come to learn that a majority of both the BCM and Spikes mid-lengths eject at the 2:00 position for a reason. The reason is so when the rifle gets dirty there is enough velocity to keep the brass ejecting and the dirtier it gets it's still able to push the bolt all the way back for the correct timing.

So the conclusion I reached is if the gun is functioning properly it doesn't really matter if the brass is ejecting slightly forward.

BradMacc82 · Apr 16, 2014

About 4 o'clock for mine, consistently. 16" BCM LW middy barrel, BCM .750 gas-block.

Ejection path isn't a science, few factors can lead you down the wrong path if you rely solely on the ejection path for diagnosis.

Ejection path can be somewhat tweaked by a few small mods.

armed ferret · Apr 16, 2014

honestly i couldn't give two squirts of diarrhea WHERE the cases eject to....consistency is a plus when at the range since i reload, but beyond that, it don't really matter. that each round extracts AND ejects properly is really the only thing that matters.

dev · Apr 16, 2014

I agree. I think it's more important to diagnose any abnormal conditions based on the spent brass and a general inspection of the bolt.

bmorewineguy · Apr 16, 2014

Good advice from all.

I built the rifle piece by piece though so just a BCM barrel not a full BCM upper. I would agree that as long as it is working it's good to go but I also reload and it was a pain in the a@@ to pick up the brass since it was all ejected off the pad in front of the firing line. I would much rather not hold others up so I can pick my brass up.

I'm hoping the heavier buffer will work out but like I said if not I will try the other options to correct it.

Proper gassing for 16" middy?

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