Adding a Half-Cock

[Zonie]

When I swapped nipples it took a 6x1mm and threaded in by hand. The 6mm nipples are a bit bigger than 1/4"...I know this because I compared it to my T/C Hawkin that takes 1/4-28 nipples. I do love using musket caps though. They open up nicely when they fire so they are easy to remove when spent.

A 6mm thread is .236 in diameter which is .014 smaller than a 1/4" thread.

A M6 x 1mm thread (used on many Spanish imports) would be equal to a .236-25 thread in US language.

A M6 x .75mm thread (used on many Italian imports) would be equal to a .236-34 thread in US language.

Notice that a M6 x 1 thread may seem to screw into a 1/4-28 threaded hole because the undersized major diameter will allow for some pitch mismatch without appearing to be the incorrect size.
Because of the undersized condition the threaded joint will be weak and this sort of thing can lead to the nipple blowing out when the gun is fired.

If there is any doubt about the correct nipple thread to be used, remove the barrel from the gun and take it to a machine shop or a hardware store and ask them to determine what size the thread really is.

 

[CoyoteJoe]

The nipple is your whole problem. The lock was built to have a low half-cock position, which is a good thing. But it was intended to work with a shorter nipple. Your nipple is simply too tall.

 

[PreserveFreedom]

I did some nipple swapping yesterday, and even with the factory nipple that has been beaten into a mushroom shape the half cock still does not catch. The only nipple I can think of that could be short enough would be a revolver nipple, if I can get one in the right thread.