Anyone have any insight on these? I saw an M4 upper with a Shaw barrel at a local gun show pretty cheap but I'm not familiar with them.

J&T uses them.  Mine that came with my JT 20" upper shoots great (not 1/2"moa or anything, but accurate as any other barrel I've tried on a non-national match gun).  Course my Wilson barrel on my ASA was accurate too, but the damn thing wouldn't work cause it's wasn't assembled properly, and the chamber wasn't reamed properly.  Be careful what you buy, just cause it's a good barrel doesn't mean it's a good deal...

I have a J&T Carbine kit on a preban Oly lower.  The barrel is a 16" Shaw, and accuracy is fine for not being a match barrel.  Functioning is EXCELLENT.  Not one single failure to fire for any reason, and now have about 1000 rnds on it.

With the iron sights, just resting my elbows on the bench, but the rifle not on bags, I was getting 1.5"-2" groups at 100 yds.  I am sure the groups would be somewhat smaller with a scope and the rifle rested or on a bipod.