If you want to lap a barrel for use with lead, be sure to go with 280 grit as an absolute minimum / 320 grit preferred.
I've never compared different brands, but several cast bullet manufacturers recommend only "Clover" brand valve lapping compound.
The 4 oz part number for 320 grit is 1A-51803 but 280 and 400 grit are easier to find. (A-51803 for 280, 2A-51803 for 400)
(The label may carry the Fel-Pro brand name, as well; since Fel-Pro owns them.)
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