Paper patching to improve a bore

[HWooldridge]

I know every barrel is different. In generalities how much is the barrel dia. enlarged by lapping?

I work in the machining trade and we occasionally have to pickle rusty items. On very light surface rust, you lose tenths but I’d figure at least .001 lost on a bad bore and it would be more on basket cases.

[kbstenberg]

Thank you HW

[Lead pot]

Some before and after photos would be great.

I can give you a before and after what a PP bullet does to the bore.
Below is a new barrel that has the reamer marks and the second is what it's now after running just short of 25 bricks of primers through it. I number the bricks for the rifle I use the primer in to keep track of the shots fired. I lost count after the previous primer shortage and started using them in different rifles.
Yes paper will polish the bore but it takes many-many shots fired before you see the effects.
I had a very dark bore in a Trapdoor that I fire lapped using 400 grid Clover lapping compound with 10 shots fired using those knurled bullets. The knurling holds the lapping compound well and works fast using black powder loads so the bullet fills the bore and groove fast. But I would use caution fire lapping it will erode the throat if you seat the bullet deep in the case. Done that.
I breach seat the bullet at the case mouth doing this and it works fine and after a few shots fired I follow up using 600 or 1000 grid 3-4 shots to polish.

[450 Fuller]

This is very valuable information. Have been reloading for 50 years, but now in new territory. I work/read with Paul Mathews
book on PP slick boolits. Have a few molds. Going slow because the rifles deserve it: an 1885 original HI Wall SS Winchester in 45-60
along with an early Shiloh Sharps "Old Reliable" in 45 2.1. Have various paper thicknesses I am experimenting with. Both bores are
excellent. Might do some polishing on a 338-06 in a pre-64 Model 70. But it is like navigating a submarine through a minefield.....