That's a good question. I don't have any hard data, but just because the 44mag is more popular I'd say they made more rifles in that caliber.
I would say the .41 Magnum is the rarest...as the .44 Magnum is very popular. Notice I didn't say better...the .41 Remington Magnum is an excellent cartridge for hunting and law enforcement. Conceived in 1963-64 by Elmer Keith and Bill Jordan, the .41 Magnum never enjoyed the popularity and success of either the more "popular" Magnum cartridges, but is still prized by handgun hunters as it generates somewhat lighter recoil and slightly flatter bullet trajectory at longer ranges than the .44 Magnum.
