The Remmy is a little different animal (and thus requires a different approach -) than the open-tops. The barrel-gap for a open-top is regulated by the arbor, but on a Remmy (whether Army [.44] or Navy [.36],) the barrel gap is regulated by the shoulder on the barrel itself, which nestles up against the frame.
To 'tighten' (reduce) the barrel gap on a Remmy you can go two very different ways. The
best way would be to chuck it in a lathe and cut the shoulder back the correct amount to allow tighten up the cylinder-barrel clearance, as was done
here.
Alternatively, should you find yerself lacking a lathe (as I did), you can still tighten up your cylinder gap (you do, however, take the risk of ruining your gun - it all depends upon your 'risk comfort level')!
What you need to do is simple, remove enough metal from the front of your frame so as to make your barrel (when seated to it's full depth in the frame again -) actually sit deeper within the cylinder recess or void in the frame. You need to first remove your barrel from the frame, and then you simply file or sand the front of your frame down the amount required to reduce your gap to your liking.
The bad thing is that you can remove to much metal (although, doing all this by hand, you'd really have to work hard at it - but still it could be done,) or (and this is what I feared I'd do when doing my gun -) "cant" the front of the frame to where the barrel would have a gap at either the top, one of the sides or the bottom of the barrel (you have to pay "anal" close attention to avoid this, as this would require taking your frame to a machine shop and having the whole front of your frame milled flat [expensive])!
Go slow, always stopping and re-screwing the barrel back in frequently (it's waaay to easy to remove too much, which opens another can of worms) to check the gap! If you have some experience cross-filing, you shouldn't have much problem (mine is a ss 1858 buffalo, had to both file and sand - all the way down to 3000 grit - to git it to my satisfaction, but it's a perfect fit now)!