I would guess you could get away with around 0.105-0.120", but it does vary with bullet (VLD, Hybrid, etc). Best thing is to call Dave Kiff (if you want a PTG reamer) and ask, he is usually very helpful and knowledgeable. I went with a 0.112" for my Dasher, which has a tad shorter neck. I am planning on using the 105 Hybrid.