The internal diameters of both the milspec and commercial carbine style tubes are the same, so they use the same size buffer. It's the outside diameter that's different which is why a milspec stock won't fit on the larger commercial tube. If that's the case with yours then yes you need a commercial size stock. The standard carbine buffer is a standard weight, about 3 oz. A heavy buffer - H buffer is a little less than 4 oz.
The biggest issue with assembling an AR isn't so much getting the parts together right - it's getting the right parts together.
US Army 1966-69, VFW Life Member, Retired Geek
Last edited by Quentin; 07-11-2012 at 05:40 AM.