twist
The slow 1-38 twist in most of the contemporary .44 mag carbines has always been a mystery to me also. Ruger finally upped the twist rate to 1-20 with the 96/99 series, but now those carbines are gone too.
My own early Ruger auto carbines (1-38) have responded well to lighter (shorter) slugs, and I've pretty much settled on 200 gr bullets from them on deer. Lots of guys report that 240's shoot well in their 1-38 twisted rifles, regardless of make, but my two don't.
Part of that may be that I tend to load for the carbines modestly to avoid wear and tear (there are NO parts out there to speak of) and my slightly lower velocities w/ 240's, a bit slower than factory and max loads, may contribute to innaccuracy. I suppose I should experiment a bit with some factory 240's, but I really don't have any complaints on deer with my 200 gr XTP reloads.