Following a process I found in a 1930 something gunsmith book by Clyde Baker,
I lapped a barrel once. It was not chambered or crowned yet. I cast the lead laps in the bore around a modified brass wood screw attached to a one piece GI cleaning rod.
This was a poor barrel,with definite tight/loose spots. Did I work miracles? Well, I worked out the tight spots,and it tapered slightly smaller at the muzzle.It took time and effort and I learned appreciation for good barrelmakers.
I screwed it in a Rolling Block . Made a 40-70 Sharps reamer on my own with a spin-dex rigged to a Bridgeport that was spinning a cup wheel on a slotting saw arbor. Reamer cut good!
So it was my leap into BPCR ,getting started casting bullets.
Thats a whole lot of new ground to cover. Did I get great results? Nothing I'd brag about. Between 3 and 4in at 100 yds, And truth be told... I leaned it in some corner. I had an interest fizzle.There is a lot to learn with BPCR.
But I did learn that its extremely unlikely, if I buy a quality custom barrel.that I, as Bubba Gun Hack am going to do anything to improve a Kreiger or Bartlein or Lilja or Douglas barrel.
What I have done is taken a loser,copper smearing 2.5 MOA barrel ...one of those < $ 100 "bargain" Brownway or Midells barrels.....And figuring I had nothing to lose, I fire lapped it with cast 30-30 bullets and some mold polishing diamond compound . It was a "No Worries" project.
That doggone barrel quit fouling and started shooting about 1 MOA at 300 yds!
I'm done with "bargain" barrels. But I'd firelap a barrel where I figured I had nothing to lose.