How or what would one use to plug the bore for a bore casting? I would think that a paper or cloth wad would be forced down the bore with the weight of the lead or it will not seal well? I know to put a brass knocker in the bore first to remove the casting; or I could use a sinker and hammer it in the bore but I don't really care for that method. Just a little worried I might get it stuck.
Any suggestions? Thanks

I have only used the sinker method you speak of. Another way is to get a conical bullet larger then the bore. Say you have a .502 bore, a .505 conical can be drilled with a hole through, a STRONG cord pushed through and a nut tied on the end.. then push that in. Pull it out with the cord. Then you can measure the lands and grooves of the bore.

I've never poured moulten lead in a bore either. Just hammer a slightly oversize soft lead ball or bullet into the oiled bore and tap it out with the pre-inserted brass rod. If you don't have an appropriate size brass rod, just wrap a steel rod with tape to protect the bore.

Normally you would use steel wool. A simple easy way to get measurements is to find a lead ball 10 to 20 thousands larger than the rifling put 20 grains of powder drive the ball in to the barrel and push it all the way down on the powder and shoot it into a large wad of cotton batting with a card board backing 4 or 5 inches thick. When you retrieve the ball your measurements will be the same as if you got them the hard way.

Another method is to use Brownell's Cerrosafe.

http://www.midwayusa.com/product/462...g-alloy-1-2-lb

This Youtube video shows bore casting at ~6:45:

http://www.youtube.com/watch?v=DByaASz_HNk