Well, we had a couple of pretty good threads going on it a while ago, but I can't get the search engine to find the best one now.. Here's the one I
was able to find:
http://castboolits.gunloads.com/show...ght=paco+kelly
Read the whole thread.
Basically it involves pushing the cartridge into a die with a blind end, using just enough force to squash the nose a bit. The
original intent was to put a flat on the bullet nose for better "terminal effect", but it also expands the diameter of the bullet to match the inside of the die. THAT makes the bullet a better fit in the throat, which improves accuracy.
I made a die set that works like the Neal Waltz system, which is much better than the Paco Kelly tool. I can send you my sketch of the die and the punch if you like. You'll need a lathe and an old .44 Magnum die with the 1/2" thread top plug, and a .2250 to .2255 chucking reamer.
I did a lot of testing of this, using an old 10/22 (stock barrel) and cheap bulk ammo, and found that it really did improve accuracy quite a lot. But simply bumping cannot make up for other deficiencies such as bullet weight, primer compound uniformity, and such. The best combination in that 10/22 was weight-sorted and bumped CCI MiniMax ammo.