I want to bush the firing pin hole in a Martini Cadet breechblock. Made up a drill guide to drill from the back for a no. 29 drill. This block is very hard and a new drill bit won't bite. I will probably make up a heat sink and try to spot anneal the block face, but it occurred to me that a spot of TIG weld filling the hole from the front would be soft enough to drill. I could file and polish the breech face and make a guide bushing to fit the receiver barrel threads and drill from the front, avoiding threading the block for a bushing. Anybody ever do it this way? Anybody foresee any pitfalls to doing it this way?

I weld up with O/A and drill from the rear on the cadet block. The firing pin should be reduced to have a slight taper like the Rem.742 and about the same size. I use a small reamer from the rear to get the taper inside. This will help prevent breaking of the tip on these actions. The tip sould be about .058 dia and about the same amount length wise in the fired position. I also use a short section of barrel threaded into the receiver and mill the block face to make sure it is square to the chamber.

You can have the block re case harden.

What Les said.
Regards, Joe

Haven't done it personally and I am not familiar with the geometry of the firing pin hole, but I would think that going into the face of the block with a bushing mounted in the receiver threads would result in a better centered FP hole. If the existing FP is pretty well centered and you're just trying to make the diameter smaller, maybe it is a horse apiece. Is the FP in line with the bore or does it hit at some angle?

gzig5, the firing pin is in line with the bore. The original pin tip and hole in the breechblock is just too large. I can see the wisdom of drilling from the back, keeping the hole in line with the pin body. Mr Brooks, what is that reamer you use, some kind of taper pin reamer? Thanks much for the advise,I wasn't looking forward to trying to tap that block.

FYI, here's a pic of the fixture I use to bush Cadets. It's basically a short section of chambered barrel stub with extractor cuts already made.

I thread it into the action face, mark the desired striker location through the case's flash hole onto the face of the welded-up-&-cut-back breechblock and then remove the block to drill it from the front. When all is finished, I can put a primer in the empty case and check the strike right there at the bench without a lotta trouble.

Les clued me into the idea of a small block-facing cutter guided by the threaded bushing, to cut the block face perpendicular to the bore line. SUPER idea!

To cut the striker nose relief taper out to the inside rear, I use a tapered round needle file inserted through the block from the rear. I rotate the needle file in a COUNTERclockwise direction and I try to be careful not to stroke it in-&-out if at all possible. The rotation is the desired action here, and the COUNTERclockwise direction will keep the cutting edges cutting smoothly without sticking. I observe the cutting action from the front of the block and when the taper reaches the front face then that's time to stop.

A tapered reamer would accomplish the same thing but not everyone has them in the desired size(s).
Regards, Joe

I have had to repair bushings in these blocks which were silver soldered, drilled and tap, and soft soldered. The best way is as mentioned in my attachment which I sent to you. The reamer is a half reamer made out of spring steel or drill rod. It has to be harden and spring steel seems to be the best steel. Shape the cone first and then harden in oil 30 weight. Draw to very light straw first, then grind down to 1/2 dia. without over heating then stone back the cutting edge on the back side like a regular reamer. It will take about 15 minutes to make and if you break it off make over and draw a little more the 2nd time. Reaming has to be done from the rear with a guide made to fit inside the breech block like a firing pin. Did you look at the email I sent to you?

my last one rather than bush i tig welded the hole shut and redrilled (solid carbide bit)