Gunsmithing M-14 action hardness

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Augustus

Guest
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

Gunny Sergeant
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Minuteman
Jun 6, 2009
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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
 
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Augustus

Guest
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

Sergeant
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May 11, 2008
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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

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May 11, 2008
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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
 
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Augustus

Guest
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

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May 11, 2008
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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.
 
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Augustus

Guest
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.
 
A

Augustus

Guest
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

Sergeant
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May 11, 2008
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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.