I have an 1839 contract musket with nipple not wanting to come out. Friend at gun shop will do what ever to remove it. It appears the threads maybe smaller than 5/16. Did some conversations use 1/4 nipple?
No, the U.S. military nipples of that era were standardized. I have seen a small commercial nipple threaded into the remnants of the original military nipple. But, that was only a couple of times in many years of experience!
J.
When using torch on nipple there was some popping going on. Seems it had some hardened powder in the breech. Surprised it happened considering it was soaked in water and scrubbed.