Reports of DD SBR barrels being over-gassed?

[Noodles]

UPDATE: No, not overgassed exactly. See post #40 for full description


Without getting to much into, does anyone have first or second hand reports of DD barrels having too large of a gas port in their 12.5 barrels?

My gun:
DD 12.5"
lo pro pinned
A5 kit with A5H2 or A5H3 buffer
Nickle boron bcg
forged upper/lower
Surefire socom flashhider
6.6lbs unloaded

I just finished up a class this weekend with Magpul. Of the 8 or 10 rifles there, mine CLEARLY had the most recoil. I have videos of Steve Fisher running his gun fast, and mine, there is a noticeably slower cadence with my gun. For anyone that doesn't know him, he's not a small dude. Probably not joking, at least three times my upper body size, I can see in the videos my gun is pushing him around a lot more than his gun (16" midlength, H2, battlecomp or tripletap)

Now, obviously, I have a carbine vs midlength, I have a flash hider vs brake, but even for the guy next to me running an 11.5" with flash hider, it's a noticeable amount of extra recoil.

My guess is that DDs run overgassed. Can anyone confirm? I won't get into BS ejection pattern, but I will say there are no obviously marks on my brass, and the ejection is quite predictable. If I had one to test, I'm almost certain this gun would easily run an A5H4 unsuppressed.

The next step is to use a MicroMOA gas block, but I haven't contacted them yet, so that isn't set in stone. I would be greatly looking forward to an adjustable block with a suppressed setting. I can't run the switchblock on my gun because of the NSR rail.

Thoughts?

[Iraqgunz]

Why don't you contact DD? FYI- my BCM will also run with an -4 buffer also unsuppressed. As will my 20" rifle and my Colt 6920.

[steyrman13]

There are so many variables listed it is hard to say.
First, everyone handles recoil differently from each other.
2- his was a 16" vs 12.5"
3- the 11.5" could have been shooting weak PMC Bronze vs your XM193 hot loads...
4- Take the gas block off and measure the diameter of the port if you suspect it to be too large

[Clint]

Have you measured the gas port?

What direction are cases ejecting?

[sua175]

well its obviously not too over gassed as it is not malfunctioning. So this might be a bad thing when going suppressed it too overgassed. but if it is that bad then like you said I would be looking at a adjustable gas block and/or heavier buffer.

No experience with 12.5 but my mk18 is gassed perfectly with and without a can with no adjustable gas system. my mk18 is comparable to recoil with my BCM 11.5 set up with exact same muzzle device and buffer combo

[Noodles]

There are so many variables listed it is hard to say.
First, everyone handles recoil differently from each other.
2- his was a 16" vs 12.5"
3- the 11.5" could have been shooting weak PMC Bronze vs your XM193 hot loads...
4- Take the gas block off and measure the diameter of the port if you suspect it to be too large

1. Of course, and expected. But this seemed like definitely too much. Red dot was up and off paper every shot. All the other guns I tried including a 12.5" midlength (i know...) suppressed switchblock A5H2 with an acog was much more stable.
2. I compared 16s, 14.5s, an 11.5, another 12.5"
3. ...... I was a asshole shooting PMC Bronze
4. I will. I need to strip it down and get some pin gauges in there. I don't own a set but I'll try and do it tomorrow at lunch. I've read that .068-.073 would be pretty reasonable for a 12.5 carbine. My guess is high .070s into low .080s

[Noodles]

Have you measured the gas port?

What direction are cases ejecting?

Tomorrow. I don't know. I don't put much stock into ejection location. I can pick up a pile of brass in approx one area when I'm done.... I also spent the entire class with a guy to my right and to the best of my knowledge I never hit him once. So, if I were to guess, I would say 4-5, but maybe 1-2 as well, hard to say. It would change with upper shape, extractor and make/age, O-ring... I never put too much stock into exact location. I just care they are all staying together.

[snackgunner]

Interesting.

I recently called and asked a DD rep what the gas port size was for my DD sbr 12.5" lightweight barrel setup was and he said port size is .081 . I'm also
running a vltor a5h3 buffer system, but have no other sbr's to compare it to.

Have you tried running a green springco spring? Could that make a noticeable difference?

[Noodles]

Why don't you contact DD? FYI- my BCM will also run with an -4 buffer also unsuppressed. As will my 20" rifle and my Colt 6920.

Not yet. I wanted to crowd source an opinion and couple options. I've seen other threads that talked about DD barrels being on the high side. And I won't say who, but a guy who would know at that class confirmed he has a DD Mk18 that was definitely over-gassed from factory.

Thing is.... I get the A5 can make the gun smoother by extended the duration of the cycle. By decreasing the cylic rate and slowing everything down, it could feel "softer", but... With a high cyclic rate and high mass, it's going to have the opposite effect. If I have too much gas, a heavier buffer will still run lower than a lighter one, but I'm increasing mass which will increase recoil.

A slow light buffer (assuming perfect reliability) would be ideal. Since we can't get that we pick between a fast light or a slow heavy one as either is fine (within working perameters). In no situation would you ever want a fast heavy.

I'm wondering if the gas port size can increase linearly and at the same time cause a greater effect on recoil.

[Noodles]

Interesting.

I recently called and asked a DD rep what the gas port size was for my DD sbr 12.5" lightweight barrel setup was and he said port size is .081 . I'm also
running a vltor a5h3 buffer system, but have no other sbr's to compare it to.

Have you tried running a green springco spring? Could that make a noticeable difference?

Holy ****. If that's the case, I'm probably moving over to a BCM LW. I know those are a LOT smaller. .081 is 10.x territory.