Yep on the bore butter or similar.
But first in 1/2 cock and assembled spin a few times check for any minute binding.
Make sure the wedge isn't too tight.
Then remove the barrel again spin for binding. This will leave some minute marks to show where the problem is.
But you said it only did it when almost off.
If that is only place and time, then I wouldn't worry much.
It's possible it just new and not worn in.
I bought a 1847 colt replica a couple months back as a kit.
Mine did not bind at all. But I still used some steel wool on the arbor to check for little gotchas. Also used a very fine honing stone to smooth the hand, bolt, trigger surfaces.
The release is smoother now.
But do have some fun shooting them!