It really doesn't matter what size you bore the hole down the bbl, this isn't going to correct the faults of steel shot. The fault of steel shot isn't in the size of bore, but in the density of the metal.
Rifles are an entirely different matter than shotguns due to the multiple pellets of the later vs the single projectile of a rifle. Compare the ballistics for instance of a 180 grain .30 cal bullet with that of a 180 grain round ball (approx .50 Cal).
If for instance you could come up with little steel bullets, .130" in dia & having a round nose with sufficient length to weigh the same as a #4 lead pellet & could keep them point on as they went down range then the steel would be as effective as the lead. Doing this though is not a matter of hole size in the barrel.
The shotgun is pretty much saddled with little round pellets.
