I have 444s in 18.5" ported, 20" and 26", and each wears a different twist. I have found that if you want to shoot cast slugs then the twist really doesn't matter as much as fire lapping or bore lapping the barrel to remove obstructions and roughness. Once this is accomplished you can shoot gas checked cast slugs anywhere from 240 - 405 gns with excellent accuracy. My 26" tube loves the Beartooth 335 gn slug and gives me a one-hole 3 shot group from a bench at 100yds at probably 2300'/sec. My 20" likes the 330-335 gn Beartooth gc slug but prefers the Beartooth 300 gn gc and that one gives me the same accuracy at the same velocity. My 18.5" Timber Carbine really likes the 300 gn casst gc Beartooth and moves them out at a bit better than 2,000'/sec. The 18.5" barrel wears a 1:20 twist, the 20" bbl wears a 1:38 twist and the 26" tube wears a 1:26" twist. HTH.
