Eightbore, I think you might be a bit confused. Do you know what striking is? It's FILING, by hand. Can you imagine the amount of material that has to be removed by filing the entire length of the barrels around their diameter, vs. simple boring or honing of the I.D.? You can polish external pits relatively simply, but a gun that has major pits inside the bores from lack of proper cleaning/lead fouling, primer or powdwer corrosion is far more common and requires a lot more material removal, generally.

And not "drilled" but bored or honed.