I set up an old barrel in the lathe yesterday to turn down the shank and thread for a LR Mauser. By the time I made a few light cuts and measured I had overshot and it was already down to 1.040". There is plenty of meat forward for a redo, but I wanted to seek knowledgable opinions on how much effect this would have on safety and fit before I did so because I am trying to preserve barrel length. Thanks.

IMO there's not enough thread depth remaining. Plenty safe except that the barrel may come flying out of the front of the receiver!

IMO set it back and rethread.
Regards, Joe

Thanks. I knew in my heart that was the right answer, but wanted to check anyway...

quote:

Originally posted by J.D.Steele:
IMO there's not enough thread depth remaining. Plenty safe except that the barrel may come flying out of the front of the receiver!

IMO set it back and rethread.
Regards, Joe

Isn't anywhere close to being safe. With a major thread diameter of 1.1, losing approximately half of your thread depth on a coarse 12 pitch thread won't cut it.

BTW, if barrel length is critical, you can turn the shank down and make a good fitting threaded adapter which would be perfectly safe. But if you can spare the .630 length, then do as Joe suggested and redo it.

Thanks Westpac. I should have measured/calculated thread depth and figured the % I was thinking about giving up before ever asking. I will file this one in the stupid question file.

Barrel length is far from critical. It is currently 22" and I was planning on chambering in 30-06 so I just didn't want to give up anything if I didn't have to. Plenty legal in terms of length, and .630 is nothing really...

FYI, this will be my first attempt at threading a barrel. It is a $10 or $20 gunshow find that I have had laying around for a while. It has a big fat, long shank, but it is turned down to somewhat of a sporter profile towards the muzzle. The outside at the shank end is very rough, almost like original scale from a forging, but the bore looked good. It slugged out right around .308, although it got a little tighter at the muzzle. The guy selling it didn't know much about it, but thought it was some sort of milsurp machine gun barrel. No threads, relief cuts, or any chamber to speak of. No clue how it attached to whatever it attached to, looks like it was just lopped off. Anybody know what this might be? I can post a photo later this evening.

Sounds like you have it perfect for a M95 Steyr project.

quote:

Originally posted by montea6b:
I set up an old barrel in the lathe yesterday to turn down the shank and thread for a LR Mauser. By the time I made a few light cuts and measured I had overshot and it was already down to 1.040". There is plenty of meat forward for a redo, but I wanted to seek knowledgable opinions on how much effect this would have on safety and fit before I did so because I am trying to preserve barrel length. Thanks.

Well, I'm not sure I will do that again. Not with this lathe, and certainly not on an expensive barrel...

My little Chinese 9x20 just doesn't go slow enough with enough torque to do this job right, but I got 'er done. 12 TPI at 130 RPM (and with no way to brake the chuck) leaves little margin for error. I elected to leave the half nut engaged and reverse the motor each pass, so I had to time the shut down precisely to let it coast down and keep the cutter from crashing into the shoulder.

Perhaps the selection of this technique was my downfall...

Anyhow, I still crashed, (lightly) stalled the chuck and chipped the cutter several times. Other times I'd stop early and have to goose the throttle or force the chuck by hand to break off that last curl. Lots of choice words uttered.

It looks OK though. A couple more light passes to take the threads to full depth and allow the receiver to screw on should be all that is needed. Then a clean up pass on the shoulder to remove the evidence of my poor technique!

You didn't happen to get that on video did you? Something like that might win you enough to get yourself a machine with a foot brake. Cutting threads by leaving the half nut engaged and reversing the motor can be a little challenging even for a seasoned pro. If nothing else, get an old barrel or pipe and practice, practice, practice using the half nut like it was designed.

quote:

Originally posted by Westpac:
practice using the half nut like it was designed.

+1

Thanks guys, I will.

KC, from your signature line:

quote:

Originally posted by kcstott:
I can't help you if you are to stupid to follow directions.

I know this wasn't intended DIRECTLY for me, but since the shoe fits... I'm wearing it!