Buy Marshalls Technical Manual. He explains everything. What he recommends is 320 grit Silicon Carbide lapping compound. It is aggresive enough to cut, but not so aggresive that you will oversize the bore in 20 or so shots. Remember firelapping is nothing but controlled wear! If you use too aggresive of a compound you can overdo a good thing too fast.
The 600 grit compound sounds like it would be really good for the final polish on your barrel.
I'd avoid Clover, it will imbed into the metal itself and continue cutting after you are done, long after you are done.
Used to use it for fiting bushings, them realized why they loosened up so soon, continued cutting.
Me I got some of the NECO compounds from Brownells and have had good luck with them.
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