HalfaDouble.
You likely have a 38-40 chambered rifle that was made using the closest size barrel they had in stock. At this time, they paid more attention to "bore" diameter than groove diameter. They probably didn't have a large enough order to make manufacturing special barrel blanks worthwhile. If you can drop a .427" bullet into a case fired in your rifle, you could likely use 44-40 ammo, but since you are having good luck with your loads and have the "set up", it doesn't make much sense. The 38-40 is notorious( even in old American guns) for having oversize chambers. At one time I was loading for a modern Colt clone, an original mod 92 Win. and an orig. High Wall, all in 38-40( comparing different loads). I had to set the sizing die for each individual chamber to avoid ruining all my cases. By doing this though, I had satisfactory case life( I also seated bullets and crimped in different operations).
Mike
