ndnchf,
Thank you for the range report. Very neat looking piece of Winchester history you have.
Based on your sight set up and older eyes, I would say that 1 1/2" groups at 25 yards is very good. My '73 wears a tang sight and definitely groups better with my older eyes than when it had the same narrow sights as yours.
Original factory .44 W.C.F. ammunition available at the time your rifle was made was loaded with .424" pure lead bullets and shot well in a variety of bores since the soft elastic bullet would form a perfect fit to the barrel upon ignition of the b.p.
Consider the 30 shot target illustrated in the 1875 Winchester Catalog. All rounds inside of 4" at 110 yards using factory ammunition. "Doc" Pardee said that the Winchester was steady in her performace........
For the best grouping results with cast bullets (The Winchester & UMC lead bullets were swaged.) I set any aside with visual defects and weigh within + 0 - 1/2 gr on a 200 gr. bullet. That's as close as one can get to the swaged Winchester & UMC bullets. Alloy shuld be no harder than 50/1.
Otherwise, the best groups will not be realized even with the proper sized bullets.
If you wanted to try larger bullets you could add another 2 grs or so of powder and compress it with the bullet, which, if soft enough, will increase in diameter. A measure of the diameter of the outside of the case neck as compared to current will tell if the bullet diameter has increased. Once you get it to the right diameter make sure that the increased neck diameter will still fit the chamber before loading a quantity.
I would say, though, that based on your results, the bullet is bumping up to be a snug fit in the barrel. Loading the best bullets (no flaws, weight variance heaviest - 1/2 grs. will improve the grouping ...... better sights would also help.
w44wcf