If you can get a Trapdoor that is over 50% on the exterior, but has a shot out barrel, I would get it sleeved. Bob Hoyt in Fairfield, Pa does an outstanding job straightening and sleeving with a chrom moly correct twist sleeve that you can not tell from the original. For $200 to $300 you will have a straight shooting, original Trapdoor that can handle substantially more (notice quantity, not power because you still have the Trapdoor action) shots through it, and will even handle jacketed bullets (if you request a .458 barrel instead of traditional .459 barrel). Regarding whether or not to make it Carbine length or retain the original rifle length, that would be personal preference. Since it is already being mutated by sleeving, it probably would not change the value. Besides, value is the least of your consideration, functionality is the key to enjoying...unless you like safe-queens and wall-hangers.
The top one in the top picture was a mutated, home made carbine that was thrown away because the dude did not research. He cut a pristine stock with all the cartouche's way too short, and cut the barrel at 19" which is 3" shorter than what a carbine is supposed to be, along with dovetailing for a front sight. I picked it out of the garbage and polished out all the rust on the receiver and barrel (had excellent rifling and bore), crowned the barrel, stuck a .673 Marble front sight in it and took 'er to the range. Turns out this is an excellent shooter. The second from the bottom is an original carbine, it had a shot out barrel. Used it for a year as a .410 and actually shot a nice Turkey with it. I have since had it sleeved by Bobby Hoyt, it is an absolutely dead nuts accurate shooter now. The rest are still original, including the rifle, which shoots just fine. Just remember the originals have very, very soft steel barrels and will be shot out quickly since by the time we get 'em they have generally had a ton of lead through 'em. The bottom Cadet model in the first picture probably has a best original bore since it was plugged with lead in 1903 when sold to the Southwest Texas Military Institute after being made to Cadet specs by the Alabama Armory after the Spanish-American War where it was first issued by the Springfield Armory, yet it never left the Alabama Armory since it was issued to a "colored" regiment and they were not allowed to have the guns until shipped out of the country. They never were.
