I thought so and not to sound discouraging but good luck! I know how undersize many factory slugs are or at least were yet they still slugged up and gave very good accuracy ~ Winchester, Remington, Federal all plain old Foster style slugs and all shot well from both my Browning BPS and my old cut down Cooey single shot. I have as yet to get the same level of accuracy from home cast and loaded rounds.
I'll say again that I think consistency is EVERYTHING! The factories have total control over hulls, wads, slugs, powder and primer and can test umpteen things before they put it to market. While they aren't perfect and don't shoot well from every gun, factory Foster slug rounds have certainly shot well in my guns all the way to 100 yards which is where I judge consistency and accuracy. In my opinion it isn't hard to get decent accuracy out to 50+ yards, it is beyond that that inconsistencies take effect and accuracy becomes "iffy" for most slug and ball loads from smoothbore.
Certainly my experience anyway.
Longbow