Thanks El Lobo. I bought the 300 BO pistol at a gun show, and when I went back several months later (same gun show comes back every few months), I asked the guy that sold it to me (was also the one that built it), what thread size was on the 300. He thought it was 1/2x28 but wasn't a 100% sure. The hand guard is oversized and covers the Noveske Break that's on the barrel. The Break is either their KX3 or KX5 model (difficult to read through the hand guard) that both come in the 5/8x24 and 1/2x28 sizes for the 300BO. I'll need to take of the hand guard and break to find out what thread size I have.