Bought a "yank" 1851 36 cal and it is a blast to shoot but after cleaning you have to give it a tap on the barrel to seat it on the locking pins. All my other pietta and uberti colts line up fine and seat tight. The navy other than that is fine.
I would like to know what the manufacture date is for your Navy. If you just purchased it, I'm willing to wager that is at least a 2015 [CN] or later.
Last Christmas I purchased a Pietta 2015 [CN) G&G (brasser) so that I could swap barrels and cylinders between it and my Pietta 2014 [CM] 1851 Navy steel.
I find that when installing either barrel on the G&G frame, I have to moderately slap it on the muzzle with the palm of my hand (no pain) to seat it, but installing either barrel on the 1851 Navy frame requires no effort at all. I am thinking the barrel lug pins alignment on the G&G is just so slightly off as to make the difference. At any rate I have no problem with it. Maybe Pietta's CNC software or their machinery is a bit off in this area these days, or the pins may be slightly different. If so, not much.
An application of gun oil may help you, but I don't normally apply oil in this location during re-assembly.
Just my $.02 worth.
Jim
Edit: I must add that the arbors are the same length on both pistols, and the barrel lug depths are the same, so the fit with all four combinations result in about a .001" gap between cylinder and forcing cone. I do keep the wedges with the corresponding barrels as the depth of the wedge fit is very slightly different but both wedges protrude far enough through the barrel lug so as to firmly engage the wedge spring.