Safely firing an antique gun

[RMFnLA]

Stick a piece of rubber tubing on the nipple and blow into it.

 

[Dexis]

Stick a piece of rubber tubing on the nipple and blow into it.

Blows through smooth with no resistance. I removed the nipple as well. Threads look clean, no corrosion, and it snugged back up well. The nipple itself appears to be quite new, flat base no tapers.

 

[cynthialee]

Here's what I do:
-make sure it's not loaded
-clean it well
-look for structural issues on the outside, including nipple, vent hole lock etc
-run a bore scope down the barrel, inspect barrel and powder chamber
-fire a cap/spark the pan
-fire light loads first, pulling trigger with a string from a safe distance: 10gr, 20 gr, 30gr, 40 gr. Swab barrel and check for issues after each shot
-full powder charge
-projectile with half charge, then again with full charge
-clean up and check for issues again

This is a solid plan of action.

Keyhole is on the money.