So the basic question is this: What's the shortest standard sized barrel I can use with my 12-inch Daniel Defense Lite Rail 2.0 in conjunction with a Surefire muzzle brake and SOCOM 556-RC can? Standard 12.5 carbine setup? Or would that be too short to utilize the QD cam/lug?

I want to snug it up close to the end of the rail and see as little barrel as possible with the can attached, while still having the option to easily remove using the QD mount, when necessary.

Anyone got an idea what I'm trying to describe and have any pictures of this (or similar) setup?

Not opposed to having my existing mid-length 16" barrel cut, crowned and threaded. But not sure how short I can go with the mid leangth system, either. 13-13.5-ish might work. But if a 12.5 carbine setup is known to work, probably easier to just swap a barrel.

Well knowing the dimensions on my MK18 with a 10.3 barrel and 9.55" rail, this is about as short as you could go with a can. Take 2.45" of additional rail (if yours is a true 12" length) i'd assume 12.75" would be the shortest. Not sure what standard size you'll find close test to that though. There is always ADCO to cut a barrel down.

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Well a 12.5 mid length works just fine. I have a great bareel in that configuration from micro moa. Beyond that the surefire take 3/4" of clearance. So you will need to know the actual length of the rail. The 2a Balios 12" rail is actually 11.8 so it would work on a 12.5 with a half turn spacer. If the dd rail is similar to this you would be fine.

I have a 10" Lite Rail with a 10.5" .300BLK barrel and it doesn't clear the threads fully.  I'm going to have to mill the rail back one rail section all the way around to be able to install my MAAD mount for my Saker7.62.  I find that, when it comes to DD rails, you need to buy the barrel an inch longer than the quoted rail length unless you're willing to do custom machine work to make your application work perfect.

I believe I was over-thinking this a bit.

I figured out that if I measure the the distance from the current barrel/muzzle brake  shoulder, to the location I want it to be relative to the rail, it comes to three inches on the nose.

Since I have a 16-inch barrel, that would logically suggest I'm shooting for a 13-inch barrel length.

Now to see if Adco or someone else can mill a 16-inch middy to a 14-inch length and drill the gas port to work reliably. Should be fine as-is with the supressor, but I'd still need it to also run reliably without too. That, or I'm shopping for a 14.5" or 16" carbine to cut down. Rather make this one work, though.

If you can figure out the right port size, having ADCO chop your 16" to 13" is probably the best solution.

That's exactly what I ended up doing: 13 inches with a slightly enlarged gas port done by Adco.

Works perfect with 100 rounds with the suppressor (but that's to be expected). Ran 300 rounds through it unsupressed. Only failure was a popped prompt on one round. But that's a problem I've been having with this batch of crappy training ammo. Been doing the same in various department guns, and in this one too, before the barre was cut down. So all appears well.

So I can attest: a 5.56 mid length gas system will run as short as 13.