Johnny2,

You can slug the bore with any lead bullet as long as you use a hammer to bump it up to slightly over bore size. The round ball would work but it is harder to keep it straight in the bore. You could bump it up and then drill a starter hole in it and screw a ball puller in so it could be mounted onto a range rod. Use the range rod to push it into the bore and keep it straight, then pull it out andmeasure the results. Another way is to use a 54cal RB to slug a 50cal bore, just use a dowel to bump it into the bore and push it through and out the other end. Good luck.