I heard horrible things about National Ordnance carbines, this is an interesting site, http://www.m1carbinesinc.com/carbine_FedOrd.html
, but a bud has been shooting his in our “M1 Carbine Match”. I took these pictures of the front of it. He has created a barrel band and bedded it in the forend. Also, something hard to tell in the picture, is that the barrel assembly is made of two pieces. The original Carbine barrel must have been shot out and Federal Ordnance drilled out the barrel trunion, turned an 1903A3 barrel down to that diameter and lead soldered the two together. Bud claims that the A3 barrel shoots better than GI Carbine barrels.
As for the claims that Carbines are accurate, that depends on your definition of accurate. They group better than buckshot in a smoothbore, but carbines are not what I consider “accurate”. I stopped shooting them in competition because there is no relationship between sight picture and point of impact.