This isn’t a Frequently Asked Question and maybe it’s not even a secret, but it is a matter that needs to be addressed if you expect to receive the best accuracy from our bullets.
Any gun that you plan to shoot cast bullets from has to be cleaned of all copper jacket fouling first. The copper fouling is much harder than any cast bullet and will act like sandpaper on the bullet as it travels down the barrel. Not only will this lead to poor accuracy but may also give you signs of leading that really isn’t occurring.
While testing cast bullets, it’s also important to keep your barrel free of leading. You may concoct a load that is a little too hot for the bullet/alloy you’re using and have a leading issue with that one load. If that leading isn’t removed before you fire your next test load, you won’t be able to tell which load gave you the problem. Moreover, leading is cumulative and will adversely affect the accuracy of subsequent shots.
But don’t despair. I’ve shot literally 100’s of thousands of cast bullets and have found a quick and inexpensive way to remove leading. I use Bronze Wool, available from Brownells, either in the fine or medium grade. Unlike Steel Wool, Bronze Wool is softer than steel and will not scratch your barrel. Also, Bronze Wool is not oiled, so it leaves your barrel absolutely clean. Simply pull some threads of the Bronze Wool off of the pad and wrap it tightly around a slightly undersized bronze barrel brush. The tighter the fit, the faster it will remove leading. Ten to twelve passes up and down the barrel will remove all but the most severe leading. If you do this regularly, you’ll never have severe leading to contend with. Bronze Wool has become an integral part of my shooting kit for years. I wouldn’t be without it!
– Dave Jennings, Montana Bullet Works