I just cut off the barrel stub at the 303 chamber neck to use as much of the barrel as possible and bore out the stub and turn down the barrel to set back into the stub ( like you do with the .22 ). a few set screws and locktite and your all set. Now mark a 21/64 drill bit at the same length at 32-20 case length and a 11/32 drill bit the length of the base to the shoulder and that will give you your chamber. You will have to polish with emery paper until the case fits. for drill stops I use a piece of 5/16 gas hose because it fits nice and snug and wont move when you drill into the proper depth. ( I know the gun smiths would cringe at all this, but oh well ). like I said I made 4 this way and the only cases that I have had any trouble with are those nickel ones.