Big shout out to Bigragu and all his help and direction. FX Crown 177cal. 500mm barrel I JB welded a sleeve onto the liner. When you do this the washers will not work Cape Fear 901 has the sleeve and the special washers needed to put in the barrel since the old ones will be too small. I took some pictures of my experience the worst group was 1/1/4" the best was 3/8" which was position F which is where it is going to stay it had one flier about 1/8" from the rest I did try G & H but they were at least an inch or so. Everything was shot at 50 yards. I shot 7 to 9 pellets at each barrel position. JSB 10.3.