45 Dragoon, the 71 Opentop is a Uberti. The date code (just checked) reads "CI" but I can't find my date code sheet to find when that was. The gun was actually purchased new at a gunshow, maybe 2014? 2015ish?
One thing I'll say is that the gun's cylinder has a "collar" that is made, seemingly integral to the cylinder (not 100% sure about this) that is apparently a Uberti introduced design intended to mitigate against gunpowder residue gumming up the cylinder with the arbor. Trying to drive the wedge in further, to me .... seems not a very good idea. Possibly it would bind the cylinder against BOTH this collar and forcing cone?
I have always tried to be careful reassembling this ---- and other --- repros. The cartridge conversions and opentops that Uberti has made have introduced differences, atleast from the cap and ball guns, if not original Colt made opentops, such as the aforementioned antigumming collar, as well as a screw above the wedge with a chord cut-out. I honestly don't know if originals had that, or not. But I try to reassemble the gun exactly as it was originally. As I said, the tiniest washer I have made it impossible to replace the barrel to frame. I did not try to force it beyond what I thought reasonable at the time, but tried to keep the alignment straight, since obviously the two parts must properly align to fit together in the first place (!).
I "think" this Opentop might be correct .... which sorta begs a question; if Uberti Colt's all have short arbors, what did they do wrong on mine?
I have to admit I do not have your expertise or experience with fixing this probkem, or working on other aspects of these guns. I can only say I am unable to show my Opentop has a short arbor.
I'll also say this; Yes. IT IS A REAL CONDITION. I'm not claiming it is not. I have Colt Ubertis I bought in the early 1990s. I'd never heard of short arbor then. I also have modern Ubertis.
All of these cap and ball guns have short arbor. EVERY. SINGLE. ONE. 1990s-present.
Some of my 1990s Ubertis have been shot a lot of times. All seem ok with no mashing of wedges, or metal around the wedge slot. But all have washers in them now.
Maybe I
did get lucky with that 1871 Opentop. Maybe. I'll take my luck anywhere I can find it!