Any one have a guess as to how much pressure it takes to flow the primer into the firing pin on the martini cadets? Will reducing the pin dia. get me closer to pressure problems with my 310 in 222R? Im  not sure wether the problem is the large hole or hot load. makes action hard to get open with primer in the hole. Im open to any suggestions.
Tom

I too have had problems with primer flow in the Cadets. A stronger mainspring is a possibility but I've tried it several times with mixed success, also a stronger spring will make it more likely that dry-firing will damage the striker. Martinis should never be dry-fired without using a snap-cap or similar since the striker may already have one leg cracked, and if the other one cracks while loaded and cocked, the shooter could very well have a catastrophe. Dry-firing without a snap-cap allows the striker to bottom out on steel which is more likely to cause cracking. Don't do it!

It's been my experience that bushing to a smaller diameter pin is the only sure solution when using the small primers. I just finished doing it to two of mine.
Good luck, Joe

Bushing the breechblock and soft soldering a music wire pin into the firing pin body is the way to go.  I set the pin for about .040"-050" protrusion to a slightly flattened hemispherical shape, with the radius forward of the breech face at full protrusion.  On my 12/15 converted to centerfire for the .357 Max. case, I found that after about 4,500 rounds, the bushing set back into the breechblock from primer pressure, so I re-cut the block for a dovetail bushing made from 1095 steel, heat treated like a soft spring.  No more problems!

David
Montezuma, IA

Strength would not really be an issue - just cartridge size be cecause of the small barrel shank - you still need chamber walls thick enough, which can be a problem with some rounds.  FWIW, it has been made up into 5,6 x 50R, which is like a .222 mag on steroids, without any ill effect...
Anything .222 won't be able to overstress the action.  And the primer flow you are experiencing would rather be the issue of sloppy firing pin fit and oversize firing pin, not of too much pressure from the round - which is why you had better bush the firing pin.

I don't recommend welding the breechbolts unless you'll be re-heat treating them afterwards.  You can end up with a too soft primer support area, or even too hard in that area.  You will be much better off with a mechanically fitted bushing, either the screw type or a dovetail type like the original Martini Enfield .303 conversions.   

David
Montezuma, IA