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I know this is an oldish thread, but what the hey.

I saw ball-burnishing at Parker-Hale about 50 years ago.

Basically, a series of very hard, very precisely dimensioned highly-polished steel balls are pushed through the bore from the chamber end to the muzzle by means of a steel rod that is very close fitting to avoid buckling. The next ball in the series is larger by a couple of .0001".

I was shown micrographs of before and after tubes and the improvement in finish was remarkable. PH strongly believed that the burnished barrels with their very smooth. work hardened rifling surface gave excellent resistance to copper fouling, were especially easy to clean and had excellent wear resistance.

In my second career in the defence industry, I watched hydraulic cylinders of up to 150mm bore undergoing the same process at Nummi Oy in Finland.

But won't that just affect the lands leaving the grooves like a ploughed field in comparison?

All I can tell you is that ball burnishing did not affect the grooves - here is the explanation from PH.