Well....Last Sat. I spent 7 1/2 hrs. doing a barrel break-in as per Sinclair International's instructions for moly-coated bullets.  I was working with a Sharps Borchardt chambered in of all things.. .25 Ackley Improved Krag.  I needed to fire-form cases & though rifle was built in the mid 1960's..bore condition looked to be unfired.  I was using a mid-range H4895 load with 100gr. moly-coated Speer Spitz. for the .257 Roberts..about 2800 fps.  First shot left copper on very edge of lands at muzzle.  After cleaning, 2 shot fired & now a thin copper wash was present on top of lands..but only on the edges..middle of land was black..and grooves never did copper.   
    When returned to work, we drew up a Cad dwg. of rifle bore..though I wasn't 100% sure of rifling land width..so I estimated .050" wide.  Anyway, I came up with a concave radius on land top with a depth of .0025".  This I surmize was reason copper was only on edges and not middle of land.  Spoke with tech. at Sinclair & he opined that if brl. was button rifled..grooves would be under most stress & metal burnished smooth & work-hardnend & less likely to collect copper?  I don't know who brl maker was..but gunsmith was a Mr. Durham of Denver.  I was just curious of land width of my .22 Hornet Shilen brl...I guess I could examine some saved fired slugs I have.
   One thing that surprised me during brl. break-in..Sinclair suggested shooting a 3 shot group when arriving at this stage of shoot/clean sequence..I figured it to be a waste of time..but set up target anyway.  1st 3 shot group printed 2 1/2"...just what I thought..waste of time..but after cleaning next group was 1 1/4"..that got my attention..next was .900"  & next was .800.  Final two 3 shot /clean 3 shot groups were shot on same bull and went into 3/4" with all but 2 cutting into each other.  Never heard of accuracy improvement during break-in..only easier cleaning.  Interesting!

From my small bit of experience with new barrels, the better the finish in the rifling, the less improvement during break-in process. If the bore is a gorgeous, highly polished finish, they seem to shoot as well with the first few shots as they do a few hundred later.

Thanks John! The only barrels I've purchased new were for cast lead shooting rifles.

I think you hinted at the solution to the measurement problem when you mentioned
recovered bullets. Shoot into water, recover and measure by the best method you have
available. Calibrated eyepiece on microscope would be best... al la .. ballistice lab but
shooters are innovative and I'm pretty certain you can come up with a good answer. 
Local HS science lab teacher might be able to help.