if hern cast their barrels horizontal, that mean the mold is filled from the bottom ( side in this position ) and up
so they first heat all the liner in its full lenght at just a tiny spot first and more and more when the mold is filled
maybe heating the full length from just the bottom and slow fill it will make it less round
I dont know , just a thought
I believe it would be much better to cast it vertical and fill from the bottom of the mold ( from the breach of the barrel )
when the mold is half full when poured in a horizontal position you have half the liner hot and the top half still cold
maybe that also could bend the liner slightly that you also get a curved bore, as half the liner is hot and the other half cold
just thoughts, any idea guys ??