If you have a bounded weapon and if that weapon is also one of your major or minor skills, you can max out it's attributes by doing a simple trick:

Just hold L, R, and X. You should hear a sound as if you're changing weapons, but if done correctly you didn't. The game will also slow down for just a bit.
Hold all three buttons for about a minute, or however long you'd like then check your stats.
They should have increased by an enormous amount, and you'll be perfect using that weapon.