Mine and most 1:12" barrels shoot the 45gr Win Whitebox ammo inside ½", I've never had to handload for it since it shoots that ammo so good, most do. Unfortunately, it's no longer available. Read the accurizing tips in the FAQs, hundreds have been in your shoes before you, you aren't the first, nor the last to be there, read the FAQs, that's what they're there for, pay close attenion to the Handi Basics 101 too. If you want heavier bullets to shoot well, try the 63gr Sierra Varminter #1370 or the 64gr Win PP, they both shoot very well in 1:12" H&Rs.
If your frame was made since 1999, you can get any barrel fitted you want except a couple shotgun barrels, the 1:9" twist 223 bull and standard barrels are all they sell now.
Tim
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