[bayman1975]

Does any body know the size and threadpitch for the screws that mount a scope mount to the barrel? The mount is for a Winchester actually. I'm in the process of fabricating a scope mount for my huntin' buddy's crossbow, but I don't have the right size tap. I believe it's metric, but am not sure.

 

[flintknapper]

I thought I could just open up my Brownell's gunsmith tap and die set and tell you, but there are 11 taps in there!


The two sizes that "look right" are #8, but there's both 36 and 40 TPI. There's #10 32 TPI as well. That wasn't a lot of help :smack:

 

[ronpip]

I won't swear to it but I'm pretty sure it is #6 x 42. Hope this helps.

 

[Ex-Sox]

My T/C Contender is 6-48. I would call Winchester just to make sure, tho.

 

[bayman1975]

I believe you're right on the #6, and it could be either 42 or 46. It's pretty fine thread.

 

[flintknapper]

OK, I pulled some screws from a some of my mounts, and they're all different sizes. That esplains why I've got so many taps in my set....

The main thing to consider is that when you settle on a size, you need a starting tap and a bottoming tap in that size. A starter tap has tapered threads on the front to ease starting the threads, a bottoming tap is square on the end, so that it makes threads all the way to the bottom of the hole.

Most of the time you're drilling and tapping shallow holes in a reciever or a barrel, the bottoming tap makes sure you can use every bit of the hole you drill.

I've also got a devise called a "tap ease" that keeps the drill bit steady and 90 degrees to the barrel, it also has a groove in it to help center the bit on a rounded receiver or barrel. It's just a set of hardened collars that fit into a jig to hold the bit straight.