I have bought a few barrels on the site here and generaly they fit one of my frames. I recently got a 17 m2 barrel and it was a little short to fit my 17 hmr frame. so I put a small diet coke shim in and it locked up fine. 2 is to tight. I went to range and tested her out. first couple 5 rd groops seemed big, few inches at 100 yds. but 3rd and 4th were right at an inch with 3 or 4 of the holes significantly less. I guess we just had to warm up to each other a little, or I had to stop shivering from the snow blowing up my coat tail. So I guess tonight I will have to get busy detempering my .002 feeler guage and JB weld it into place for permanent. I sure do love the way these little .17s shoot. Thanks Don.