On the SLR thread, or somewhere, there was mention of a group buy from Faxon. Their Gunner weight 20" barrel has a match chamber and is listed at only 1.5lbs. If the group buy doesn't materialize, I would consider buying one of them and importing it myself ($199US price). Then I would chop and inch or so and leave it without threads.
Faxon also has a nice looking light weight bolt carrier group that only weighs about 9 ounces....
Can someone tell me why these guns need either a muzzle brake or a flash hider? In an 18-20" setup for a varmint rig, what it would matter? Is it a must on a 7-10" build? I haven't ever shot one that short, are they flame throwers?