Hey thanks for the replies, I ended up calling TC and they confirmed that the 10" barrels they made were a 0.308" diameter bore. I was looking through my reloading manuals last night and was able to find data for up to 150 grain bullets - I was hoping to use a 180 grain. Specifically looking at the 180 NBT, 180 SST, or 180 Interbond - are any of you loading heavy bullets in a a 7.62x39? If so what bullets / loads are working for you? I noticed that there is data for the 300 Whisper with heavy bullets - I am thinking that may be a good starting point if nobody has good data.