I purchased an IMA brunswick musket untouched and also a parts gun. Components are different sizes on the two! I guess Nepal guns are all custom built. After cleanup I calculated the stress in the barrel steel is about 11000 psi with a 120 gr 2Fg load and .690 ball. Since mild steel yield strength is about 40000 psi I used 110 gr for a test load with no problem.
I did encounter some gas leakage around the nipple probably caused by its poorly made threads. Its the same 5/16-18 thread of the Enfield musket so I bought some Enfield nipples but found the hammer throw (distance between pivot point and center of nipple) is incorrect and the hammer offset (distance from lock face to center of nipple) is wrong also.
After some thought I concluded I can make a hammer from a 1 1/4 x 1/4 steel bar and mount a 1/2" diameter cylinder on it in the correct place and weld the two pieces together. Using two pieces I can adjust everything in place so the hammer impacts the nipple squarely and centered.
Has anybody else tried this?