So, I am starting to doubt my choice of an Atlas S1 12" with a 12.5 barrel.  The threads are just inside the end, but I think with MD attached it will vent just outside.

What is the closest people have run this without issue?

I know there is that thread around here with the split rail ends of awesomeness.

I also know about the "what length rail do I need" sticky.

As long as the ports are fully exposed outside of the rail you should not have any problems.

Imgur is being weird and not letting me reduce the size of these pictures right now. Got them resized. First picture is a YHM QD mount on a 10.5" barrel with a 10" rail. This used to have an A2 flash hider and it was plenty of clearance for the ports. Second picture is an 8.3" barrel with a rail chopped to roughly 7.875". I have a 13.9" on a 13.5" rail which does have a spacer for my YHM QD mount to make sure the rail can't interfere with the mount as well as get to 16". The Reardon Plan B mount on the 8.3" would work on it too, but it isn't long enough.

Yeah, this barrel is destined to get a Rearden DPB, when they are back in stock...

Did you check their dealers? A few things were in stock with dealers a couple weeks ago when I ordered, that Rearden direct didn't have.

I'll try again. I looked at a few and wasn't successful, but I didn't try them all.

Question.  I am wondering, looking at the DPB,  to properly time it, which is the top side? I don't see anything on the website or in the box.



In this image it is flat on the top of the MD.   If I look at the channels on the tines, if this is oriented properly now (as if on a barrel), gases exiting and flowing up will enhance muzzle flip?

There are 2 channels for vertical gas escape on the end.  One way has no resistance (bottom here).   The other way has a bore pointing triangle which will evenly impart some force vertically and push slightly at diagonals to cancel sideways forces.

If that triangle is on the bottom, then it will cancel some muzzle flip.

I guess I'll send them an email.

Hopefully they reply to you! I emailed them and never heard back. I assume those flash hider tines really don't do anything for muzzle rise since the main ports are before them. If they don't respond, you could always try both ways and see which feels better.

Yeah, I was thinking I could experiment also.

The other thing that occurred to me, is that maybe they don't care too much, since it's primary duty is suppressor host...

I also sent an email last week.   No response.

If you read the descriptions, they say the black nitride gives the best seal, compared to the rainbow or wheat.   I asked what the effective difference really was.

And I ordered another Rail.  STNGR 10.5" VLCN.  
It is my second one, it has a similar profile to the Atlas S-1, but not quite as slim.



While I can use the Rearden DPB, there is no way I can attach a suppressor to the Rearden with the 12" Atlas S1.

With 10.5“ STNGR VLCN hanguard (which is best for AGB access)

Attached File

For future reference, rails that are nominally 12”, including the poorly named DDM4 12.0”, are usually ~12.5” and will not play nice with 12.5” barrels. The longest rails that work well are:
Larue Quad or LAT 11”
KAC URX4 10.75”
BCM QRF10
SLR 11.7”
Triarc Wedgelock 11.5”
FCD/CMT RHF 11.5”
Troy Battlerail 10.75”
Midwest 11.5”
G Mk8/16 10.5”
DD M4/MFR/MFR XL 10”
My preference is Larue or KAC. All of the above 10.0” and 11.0” rails are slightly longer than advertised.

Ok, I gotta ask.  Who makes that muzzle brake?