If you tried that with an open top barrel, you will find the bore larger, even though it's called a 44. The reason is as you said for the rifling machining used on the percussion guns. Colt made up the ammo for the open tops and conversions, using a heeled bullet that contacted the bore while using a cartridge case of the same diameter. Looks like a big 22. Same was true of the early 38 Colt, same rifling. When the testing for the SA was underway, they reduced the bore diameter to actually shoot a 427 bullet. I have shot several gain twist early 44's with great success if the bore is at least a 7. Below that, the pitting and clinkers drag lead off the bullet and affect its spin, and leasd the bore quickly. The Remington 75 is the real problem, for they used a good 44 bore but had oversize chamber mouths in the model 75. They just will not shoot any 44-40 with accuracy. This problem was addressed in the model 1890, so I am told.