Enlarging M70 Receiver Thread on Win M70

G

grits

Guest
Hello Everyone

In the past, I have cleaned up the receiver threads on a M70 just enough to get them square. I have heard about M70's being enlarged to 1 1/16-16, the same as a M700 Remington, from 1-16, which is stock on the M70. I have also thought about enlarging the existing thread +0.010 to +0.015,, nevertheless, to a predetermined size. That would give me one less thing to keep up with

I have a couple of M70 projects I am getting ready to start. Can anyone comment on what I mentioned above.

Thanks,

Grits
 
I believe Winchester opened up the threads on the short mag actions... and I know Bill Leeper has done the same to regular Model 70's with success.
 
grits

I've enlarged several using Dave Manson's tooling. I liked the final product but the problem is they are hard as hell. The scope base screw holes are even harder. I would bet they're induction hardened as the only area that is hard is the receiver ring. I ruined several $200 taps before it sank in that this was losing proposition. Now I Run a .010" over 1" tap, square the receiver face, lap the lugs and square the bolt face. As hard as they are I'm not sure there is any way to recut the treads and know they are true. The threading tool will flex differently as it passes over the hard and harder spots. You can probably get away with truing the exsisting threads but watch out around the screw holes. If it's a blued action you can see a ring around the holes that shows they are a different hardness.

Dave
 
M-70

There are several flavors of M-70 receivers. The post 1964 up to about 1968 with the matte finish are a piece of cake with the Manson reamer and tap setup. The STR's with the polished receivers will eat your $200 taps in no time at all. I don't have experience with the later receivers, but Dave Manson says the classics are ok to use the tooling on.
 
Method of work

Thanks for the Replies

I was planning on doing the work on a lathe, using a spider, with carbide tooling and coolant. What do ya'll think?

Grits
 
M70 threads

Recently single pointed threads on a new stainless M70 with carbide tooling, no problems.Yes they are hard. Need a very ridged setup, .001 per pass, feed with the cross slide.This was the beauty that had the receiver raceways broached right through the threads on a WSM. Made perfectly fire formed cases that were about as round as a flat tire. Wouldn't put three consecutive shots into a refrigerator @ 100yds. It gets better, this was a "Presentation Grade" and those babies ain't cheap. Hope they fired the idiot in control of that joke before they moved production south.
Regards...Herb Coates
 
Mine are older

Hello Everyone

Mine a older. One is one of the first post '64 Supergrades. It started life as an '06 and i am re-barreling it in 7x57. Another is a long action push feed that was build in the late '80's. I cannot remember what is started out as but I used it as a platform for a 280 AI. It is due for a new barrel. The third is a later Heavy Varmint push feed that was chambered in 222 Rem. It will be re-barreled in 300 Whisper. All three are CM.

While we are on the subject has anyone ever trued a Montana Rifleman action which very close to a M70 Post '64 Classic?

Thanks,

Grits
 
I have enlarged M70 threads before,like this. I made a kind of bushing
with a D shaped hole in it .This was held to the reciever ring with a
set screw . After truing the reciever face and machining the D bushing
true at the same time. Adjust the steady rest to the bushing OD.

Then the mandrel is removed,and the action set up using the steady
rest to support it .Machining the threads is relatively simple after this,
proceed carefully,taking small cuts. Threads came out perfectly and
I did not find it necessary to enlarge all that much,Although the resulting
good thread is still a bastard diameter,it's perfectly true ,the firing pin strikes
dead center.

You MAY find you need a bushing for both front ring and rear ring,but once you have them they can be used many times,just with a clean up cut each time.
 
I used to use a setup just as Kevin describes and it worked fine but for the last 10 years or so I've used a big tube with set screws to hold the action.
I use cobalt steel bits to cut the threads and now take them to 1 1/16 (started this with the advent of the WSM's and their oval chambers.) to give me a full thread for the entire circumfrence. Carbide inserts truly hated those screw holes which is why I went to cobalt steel bits.
I have trued a few MRC actions and they are a real can o' worms. The main similarity with a M70 is the trigger design and the outside contour. Inside, the differences are considerable and there are some real challenges. If anyone's interested I can take you through it. Regards, Bill.
 
I have put screws into the holes when I have opened these up. I know they are a different hardness but at least it wasn't a interrupted cut and it is kinder to the carbide inserts.

G'Day
John aka Bungalow Bill
 
I am Interested

Bill

I would really like to know the differences between the Montana Rifleman Receiver and the M70. It helps the know what is in the can before you grab the worms.

Grits
 
I'm no gunsmith, and don't intend this as a comment on anything posted here, nor do I intend to disagree with any of the previous posts. Having said that, I have seen this service listed on Greg Tannel's website for a very low price. I realize he is not known as a benchrest gunsmith, but so far as I can determine he has a very good reputation for the accuracy of the rifles he turns out. It might be educational to contact him and ask about his method.

http://www.gretanrifles.com/prices.asp

stryker60
 
Greg

I have talked to Greg. I have his bolt raceway reamer. I have also watched his videos. He is very good.

Grits
 
OK, here I go again (picture me, a ruggedly handsome middle aged man, sitting before my computer, cracking my knuckles); M70 Winchester vs. MRC1999.
The main differences between the two actions reside in the receiver ring and are the result of some design features which, in combination with some manufacturing problems/techniques, create some real challenges for the prospective action truer.
The M70 is really a pretty straightforward action and once it is set up in a suitable fixture, it is no great feat to re-cut threads and locking lug seats. For those who like the old classic style of match rifle, it makes a good basis.
As I mentioned before, the MRC shares the M70 trigger design and external contour (with a slightly longer receiver ring. It also shares the M70 coned breeching system but accomplishes it in a different way. This is, as Elvis sang, where the heartaches begin.
The M70's coned breech is machined into the barrel when it is fitted. MRC, for some reason, decided that machining a coned breech and making an extractor cut was too onerous so they incorporated the coned breech into the receiver via an internal barrel seat or c-ring similar to that found in a Mauser 98. The differnce being that the Mauser c-ring encloses the head of the bolt and is therefor made with an ID of roughly .705 to accept the bolt nose. The MRC c-ring is coned on the rear surface similar to the barrel of a Model 70. The ID of this c-ring is about 5/8 inch. This opening is small enough that it is difficult to get any kind of respectably stiff boring tool in to machine the locking lug seats. This explains why they are left "as cast".
There are some more idiosyncrasies of design and manufacture which I'll get into in the next installment. Coming right up. (I think a combination of long post and slow typing skills contributed to the loss of my last effort so I'm going to make this a couple of posts). regards, Bill.
 
I was never in Winchester's plant but if I had to make a guess, I would say the M70 receiver forging is bored from the front.
The MRC, on the other hand, appears to have been bored and reamed from the rear and only the receiver bridge is reamed. Whether or not the receiver ring is finished first and the reamer piloted by an insert or something, I can't say but I suspect not. The receiver ring is machined from the front (how else?!) and the face of the receiver, the threads and the face of the c-ring appear to be done in one set-up in a mill. All machining is done prior to heat treating.
The bore of the receiver ring ( the bolt raceway, if you will)is not machined and is cast roughly .025" oversized. As a consequence of this there is no lateral support for the head of the bolt. All bolt alignment (or not) is accomplished by the fit of the bolt in the receiver bridge. This is done to accomodate the inevitable warpage which occurs during heat treating. This warpage can be quite significant. On the worst one I bought (my own, as it turned out!) was warped to the extent that the receiver ring was eccentric to the axis of the bore of the bridge by about .032" (.064 tir). In addition the left receiver wall bowed out about .015". Even the generous clearance at the front end would not have been sufficient for the bolt to go in had it not been for the clearance in at the rear which was nearly as generous (bolt .696". Bore .708"!)
Now for a brief description of the methodology:
I turned a mandrel which was a tight fit in the .708 bore of the receiver bridge. The front end of the mandrel I turned to .600 so it would go through the ID of the c-ring. The first hint that this action had some real issues was when I found that an OD of .600 was not small enough to fit through the c-ring. I turned it to .550 and it just cleared.
I made an insert to screw into the receiver ring. I turned, threaded, and bored (to .760)this piece in one set-up and faced a bit on the chuck side before I parted it off. The threads were special. I initially threaded it using a sharp 30 degree tool (not 60). With this tool I ended up with a thread which was way deep but which was still flat on top. I then chased this thread with the 60 degree cutter to get it so the receiver would screw on. MY idea here was to produce a thread on my test piece which sat on the angle of the receiver threads and definitely did not contact top or bottom of the thread. Seemed to work out.
With the test piece screwed into the receiver ring and the mandrel slid( alright, tapped. Hard.) into the bridge and out through the test piece, the amount of mis-alignment was glaringly obvious. By setting it between centers, I was able to indicate on the test piece to measure how far out it was. As they said in the '60's, Far out!
Next, fixing the MRC.
 
Back Again.
Since this receiver was obviously way off, I decided there was little point in machining to correct it. Sterner measures were called for. Some accuracy gunsmiths and shooters may find some of these methods offensive. Reader's dicretion advised!
I set up a couple of lead blocks and laid the receiver on them with the left receiver wall facing up. Using a chunk of aluminum to protect the receiver surface, I whacked it sharply with a 3 pound hammer. Just a few well placed blows had the mandrel coming through within .005" of the center of the test piece. This also served as a form of stress relief. Not on the receiver but on me! There's something about beating on a new action with a big hammer that just makes me feel good! Anyway, with things much straighter (the receiver wall was now almost perfect!) I could go ahead and set it up in my action fixture just as I would any other action. I did so.
After removing the test piece and the mandrel, I was ready to start truing. I bored out the ID of the c-ring to .812". This gave me room to get in and machine the "as cast" locking lug seats. It was during the machining of the locking lug seats that I discovered another interesting idiosyncracy of the MRC design. The locking lug recess is neither concentric nor round! On the MRC bolt, as on many others of simlilar design, the right hand locking lug (the one under the extractor), is shorter than the other by about .025" or so. This difference is reflected in the receiver. So, when you go in with the boring bar and face the lug seats until you reach the bottom, you ain't done with the top seat yet. I just rocked the spindle back and forth while advancing the tool a bit with each "rock". It worked out fine.
All the while I had been bugged by the lack of lateral support for the front of the bolt and decided to try and do something about it. I had already bored the ID of the c-ring out to .812. I faced it back about .050 just to give a little more space for my threading tool to run into. I then cut a recess another .050 deep with an OD of .937. After I faced the receiver and re-cut the threads (ended up with a major diameter of 1.024"), I made a little insert which fit into the recess and extended through the c-ring. The ID was about .700". The thickness was such that it sat .001" proud of the c-ring so the barrel (and some loc-tite) would hold it in place. I then turned the nose of the bolt so it more resembled a Mauser. The coned breech was a thing of the past. The nose of the bolt would fit into the insert and the bolt would no longer act like it was trying to crawl out of the receiver. Everything worked out pretty well.
As can be seen, it took considerably more work to "true" the MRC than it would a Model 70. So much so that the cost of such work would likely exceed the value. This was a good day's work. In addition, some of the unique problems one can run into with the MRC make me question the veracity of some who say they have trued them up.
So there it is. A complete truing job on a MRC1999. One might refer to it as "Leeper's Folly" and not be far off the mark.
In all fairness, none of the other half dozen MRC actions on which I've worked have been nearly as bad as this one. Also most owners don't even notice what, to me, seemed like real shortcomings. Regards, Bill.
 
Bill this is a great read...

If you type it up on your computer using word or even as an email and then copy and paste the text you won't lose it even if it takes quite some time to compose it...
 
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