OK, my search didn't go so well...


Here's a plan I'm kicking around:

Midlength barrel cut to 12ish" + 4.5" perm attach XM177 moderator.

Will this even cycle? (just for range duty)
or should I try to figure out a lo-pro carbine gas block under RRA middy hg's
with a "dummy" FSB (pinned, no gas tube) in front.

trying to keep it non-NFA, but without the excess exposed barrel...

if you have a experienced gunsmith work on the bbl. then functioning isnt a problem. if the gas port is properly worked then it should work fine

Cool...
Still learning about gas pressure before and aft of the gas port!

Chopped pic to help visualize my idea, assuming perm. moderators:
(thanks rsilvers)

I was just thinking about the same project a couple of days ago. It would be easy.
You could even leave some of the barrel under the moderater to keep port preasure up.

Just reviewing my XM177 history, didn't the XM177 go from a 10" barrel to an 11" barrel precisely because having the muzzle that close to a carbine gas port created issues?

It seems to me that lengthing the barrel one inch and then moving the gas port forward two inches is going to bring up the same issue.

Possibly?

Maybe the issues really show under full auto...(which this won't be..barring a few bump sessions.)

I saw a rifle length barrel cut down to 16" running full gas tube built by Mongo,
and it seems to run all but the weakest ammo...
This would be sort a shrunk-down version of that.

I guess a slip-over moderator could help a bit, but I'm trying to keep it "kinda" authentic!

Well, the issue is going to be allowing the gas port to tap off enough gas to cycle the action before the bullet leaves the barrel. You can open the gas port up so that it taps off gas faster; but this usually makes the weapon try to extract before the case has shrunk away from the chamber (which will get worse as the chamber gets hotter).

A moderator that created a little residual pressure kind of like a suppressor (or the Novseke Krink) would probably help by letting you run a smaller gas port. In any case, I am sure you can get it to run. It just may not run at an optimum reliability.