Gunsmithing M-14 action hardness

[Augustus]

I came across an M-14 (recent production ) with messed up threads in the front scope mount screw hole. A machine shop attempted to drill and tap it. They finally got a good 1/4 in. hole drilled in it but could not get it tapped. What kind of special tap will it take to complete the job. That action is some hard stuff.

 

[cal50]

Re: M-14 action hardness

Off the top of my head I think that is a 12-32 threaded hole.
You would want the diameter to be .185" or a #13 drill. Taps are available from Midway or Brownells

If you punched it out 1/4" that's too big.


One way to fix it-

http://fwd4.me/0imK

 

[Augustus]

Re: M-14 action hardness

I think the mount can be made to work OK with a 1/4-28 screw. The problem is the action is harder than the tap, it flattened the cutting edges. I was wondering if there is a tap with enough hardness to cut it.

 

[toolmaker]

Re: M-14 action hardness

You need to use a carbide tap, what kind of machine shop could not figure this out? You should of had them install a helicoil so you could use standard scope mounting hardware. G.I.Specs for rec. hardness, case depth .012-.018 core hardness, 28-42 HRC Surface hardness, 61-71 HRD

 

[toolmaker]

Re: M-14 action hardness

If the hole they drilled in the rec. is 1/4 diameter you can not use a 1/4 -28 screw. The hole should be .213 dia. to tap for a 1/4- 28

 

[Augustus]

Re: M-14 action hardness


What kind of machine shop? Obviously one that didnt know how to drill and tap an M-14 reciever. No,seriously he thought the tap would cut it. He said he would have to get another tap, thanks for the numbers. I will pass the info to him, I will also mention the helicoil. To be honest I have no idea what that is, maybe he will, anyway Im going to do a searh so Ill know. Thanks again.

 

[toolmaker]

Re: M-14 action hardness

I dont mean to come across like an A-hole but its not about knowing how to drill an M14/M1-A receiver. Its about knowing how to drill and tap hardened steel. The minute that drill bit touched that steel and started to squeal like a pig he should have realized what he was up against.

 

[Augustus]

Re: M-14 action hardness

Yep, thats exactly right and I could tell he didnt know what he was doing, thats the reason I was asking you guys. Back to my question, will a standard run of the mill carbide tap do the job or do need something special.

 

[Augustus]

Re: M-14 action hardness

Yep, thats exactly right and I could tell he didnt know what he was doing, thats the reason I was asking you guys. Back to my question, will a standard run of the mill carbide tap do the job or do need something special.

 

[toolmaker]

Re: M-14 action hardness

A carbide tap will work, be warned they are very expensive! Once the tap gets thru the hard ''skin'' of the receiver the tap will cut like butter.

 

[Augustus]

Re: M-14 action hardness

Ok, thanks