Hello all,
I think it is a combination of the grip, barrel length, and weight and balance. I have never shot originals. But over the years I have owned several (and shot extensively) repro Colt 1860 .44 Armies and '58 Rem .44s, and one Colt 51 Navy in .44. The Rems seemed more accurate using the sights, but by far to me the most naturally accurate, best balanced and natural pointing pistol was the Colt .51 Navy in .44 (never shot a .36). You did not have to aim. Just hold it out at or a tad above waist level and just point and shoot. It was amazingly accurate that way. I figured it was due to its exceptional balance and "feel" in the hand and its natural pointing abilities. That is my take on the subject.
For what it is worth I used to have an 1875 Remington in .38/.357 and it was more accurate by far using .38 Special all lead SWC. One day I shot at some 20 ounce coke bottles at like 30 yards. Hit all around it with the .357s but could not seem to hit them but once evey so many shots. I switched to a box of .38 Specials with all lead SWC bulletts. Man, I knocked the red cap off those bottles right and left. Much more accurate to me in .38 special.
Later,
Pistolero
Alabama