Win M-70 Extractor Cut, New Style or Old?

[INTJ]

I am permanent newby and have now successfully chambered a half dozen barrels for my BAT actioned LR BR rifles. Since I am currently unemployed and the overreaction to the Wuhan Virus has delayed my return to employment for an additional 2-3 months, and since they just closed my local range (I guess having 1-3 guys sharing a 20 bench firing line is not enough social distance); I might as well finish up my initial batch of gun projects. Besides, the PM 1340GT and the PM 833T are getting lonely.....

I am a CRF M-70 guy and need to rebarrel several. I have the straight PTG cutter and I just ordered the radius cutter. Looking at all my various old CRF M-70 barrels, I see that the pre 64s and the earlier M-70 Classics used the radius cutter and angled the extractor slot. The later Classics and New M-70s just have a flat slot cut across the whole shank.

I don't see a huge advantage to the old style angled radius extractor cut, and the new style would be a lot easier to do. Still, I suppose the angled/radius slot might provide a tiny bit better gas control.

What are your thoughts on this? Is it worth making the angled/radius slot or is the simpler straighter across newer style the way to go?

 

[GenePoole]

I've always just used a woodruff cutter and they come out fine. I bought the PTG radiused cutter, but I've never used it.

 

[shortgrass]

Just take a look at the extractor cut in the coned breech of a 1903- 03A3 Springfield.

 

[GenePoole]

Found this at White Oak's website (1903-A3 barrel):

 

[PWS]

I don’t think there’s any advantage between a flat or radius surface but do think it’s reasonable to come in at an angle to minimize the amount of chamber wall removed especially since the inner portion of the nose of the extractor is angled anyway.

I’ve read about the trick of cutting the relief just short of full clearance to cam the extractor off the case when in battery, purportedly to eliminate the extractor from pushing the case off center in the chamber and having a negative effect on accuracy. Don’t know if I buy this as important or necessary and usually try to provide full clearance.

Most of the measurements I’ve taken from the extractor nose (at the forward flat, not the slope of the hook) to the bolt face run around 0.130” so I target a relief cut depth of 0.140”minus, measured from the base of a GO gauge to the chamber edge. This is roughly mimics the maximum overall bolt nose clearance I want end with, assuming the face of the extractor matches the relief cut.

 

[INTJ]

Thanks all! I guess I'll try the angled cut. I'll practice on some old barrels first

 

[Dusty Stevens]

The radiused cut leaves less exposed case on each side. You have to take a straight cutter too deep to be right in the middle and on the outside edges.

 

[Will Henry]

If you look at the extractor on a pre-64 in comparison to the latest Model 70's, you'll see that the extractor on the new one is not as thick so the flat cut doesn't have to be as deep as it would be if you cut the same on a pre-64. I don't think one is any better than the other. I've always done mine using a Palmgren milling attachment on the lathe and an end mill. WH

 

[PWS]

I got to thinking about what I wrote and if you go 0.140” deep at the edge of the chamber to the end of a GO gauge and the flat nose of your extractor is only 0.130” from the bolt face, the clearance between the slope of the extractor cut and the slope of the extractor hook will be more than 0.010”. This is deeper than the minimum necessary and the minimum is the safest.

It took me a while to figure out my own madness and it appears that I’ve already forgotten what I do!

I can say with certainty that I use a gauge and the measured distance of extractor/bolt face since it’s such a PITA to “cut and try” - just not sure what those numbers are and my notes are packed up for a move (great timing I might add...).

 

[PWS]

FWIW, the few SC 70’s I’ve worked all have flat, perpendicular cuts AND the amount of overall cone has been less than Classics and Pre64s.

 

[msinc]

.........I’ve read about the trick of cutting the relief just short of full clearance to cam the extractor off the case when in battery, purportedly to eliminate the extractor from pushing the case off center in the chamber and having a negative effect on accuracy...…..

Well, I don't know if I buy it either sir. I have tried it and also tried the flat cut vs. radiused and I cannot pick up one bit of difference on a target or been able to discern any loss of accuracy with either style. I do angle the extractor cut though. As to camming the extractor off of the case...it seems like if you are camming something wouldn't it pull on the bolt too???..... again, I couldn't see how that helped at all.
I think some people have nothing better to do than sit around and dream up ways to impress other shooters/gunsmiths. I always try it just to see, but 99.9% of the time "it" is spoon fed hog schidtt.

 

[Dusty Stevens]

This is the purpose in the concave cutter. You can see how it cuts the same width around the chamber instead of just making it work with a flat cutter

 

[INTJ]

For reference, the pics show, top to bottom:

1. New M-70
2. Late Classic
3. Early Classic
4. Pre-64

 

[buckhunter62]

I take a very course file and do it before you guys get your tools out & the machine set up to cut it' When the gun is assembled you can't hardly see the extractor cut any way.

 

[Will Henry]

A friend cut his with a cutting disc on a die grinder. I tried it and it worked fine and quickly but I prefer to mill the slot. Camming the extractor off the case is poor practice as it deflects the nose of the bolt. An extractor which contacts the barrel is often a source of inaccuracy. WH

 

[CFCA1237]

Take some pictures of your setup as you go! I am working on one as we speak...

 

[Danny1788]

What angle is the pre64 extractor groove cut at? I have the cutting tool but not 100% sure on the angle? Not the coned counter bore angle I know that already. But the angle that the cutter is ran into the threads to make the groove.

 

[INTJ]

What angle is the pre64 extractor groove cut at? I have the cutting tool but not 100% sure on the angle? Not the coned counter bore angle I know that already. But the angle that the cutter is ran into the threads to make the groove.

We need the real gunsmiths to answer. but it looks like you count six threads and cut from there to the edge of the chamber.

 

[Danny1788]

I’ve heard 30deg but don’t know if that’s right. I don’t have a factory barrel to measure just the action.

 

[INTJ]

I’ve heard 30deg but don’t know if that’s right. I don’t have a factory barrel to measure just the action.

I don't have a great tool to measure, but the Pre-64 and early Classic look to be 60 degrees. Please don't take my measurement though unless confirmed by a real gunsmith.