Hi
I received a muzzle loader barrel , that has stipped nipple threads ...short of changing the breech plug ... would it be safe to install a threaded insert , to get back the original 1/4 x 28 threads ..?
Thanks , Bob

If there’s enough room a properly fit thread insert would work fine.

Thanks , John
I just found , that they make oversized replacement nipples as well .010,.015,.020,.025 ....same 1/4x28 ...this is maybe the way to fix this ..
Bob

Or retap it to 5/16ths; that is a standard nipple size.
Or convert it to flintlock; they are more reliable when you run out of caps.

Yep - that too...5/16 would work ..