I probably have over a hundred pre-64 model 70 rifles in various calibers, factory rifles and custom rifles. I have a few, just a few that demonstrate a similar oddity. It occurs on both original factory rifles as well as full custom rifles. Here goes!
As the bolt is lifted to cycle the action things go smoothly until I reach the three o'clock position. There is a bit of significant resistance as you to the two o'clock position. When the bolt lug clears the race way all pressure is relieved and the bolt can be pulled back to chamber a round. This happens with a live round in the chamber, a fired case in the chamber as well as an empty chamber. I think I have a bolt lug set back in the contact area in the bolt race. What do you think? The thing is if you fire a round even a mild round in the chamber, the resistance while cycling is increased a bit????? Very confusing as it looks like I may have to replace the existing action on my custom 375H&H to get rid of the problem.

Are you feeling the pressure required to cock the firing pin?

I don't think that is it. We played with over 50 rifles this weekend and only 7 had this phenomenon. It feels like the bolt lug is riding in the bolt race and meets the step up, goes over the step onto a flat just prior to releasing. If that is when the firing pin is cocked I just do not know.

I think you have lug setback also. Noticeable when lifting the bolt on an empty chamber because of the firing spring tension as it is cocked riding over the unsetback portions of the recess bearing surface and more noticeable when lifting the bolt on a fired case. The increased headspace caused by the setback in the lug recess allows the case to expand larger than it would if there were no setback, as the bolt is turned on opening it moves ahead as it it rides over unsetback portions of the lug recess bearing face squeezing the fired expanded brass further into the chamber tightning the headspace causing resistance until the lug clears the bearing surface of the lug recess and falls into the lug raceways.

Check for binding in the following places. Winchester M70 bolts are known to have these spots rough or oversize enough to drag.

One, The LH lug OD will drag in the cocking cam in the front ring. This will show as a drag or wear mark on the blued finish. What it is , the raceway is slightly larger than the closing cam cut and the outside raduis of the lug will hit this few thousands and drag.
To fix, remove about .005 from the out side diameter of the LH lug so as not to bind in the two different cuts.
I had one that really tossed me for a loop once, seems the tooling cutter got wore and then they had about a .020" radius in the corner of the cam cut. The sharp corner of the LH lug just kept digging in and binding. I had to file a small bevel on the rear edge of the lug to clear the raduis in the cam cut.

Two, I have seen this a couple of times. The front diameter of the bolt where it meets the front of the bolt handle root has a larger radius than the reciver. This will cause a bind in one spot only about were you are seeing it. Then it disappears as the bolt handle drops down and the raduis then goes into the larger RH raceway cut. Had a 1961 Fwt that my cousin bought new, he had used it a lot. It always bound slightly in one spot. Found the bright wear mark in the sharp corner of the root vs the bolt body diameter.
To fix, carful use of a file with a smaller raduis or safe edge.

Three, Also the sleeve lock vs the bolt notch for it, if the sleeve lock nose is to long then it will bind as it goes into the notch since the sleeve is threaded this distance will change as the bolt is operated.

Four, Also sometimes the bolt stop is sloppy on the pin and then the rear edge of the sleeve lock will hit the front inside edge of the bolt stop and bind up. This one is hard to see as it is hidden, you will have to remove the bolt stop and then try to function the bolt. Once the bolt stop is out and it does not bind anymore then you know it is the bolt stop.
To fix, either replace the bolt stop or file an bevel on the inside edge so the sleeve lock will ride over better.

Five, Check to see that the top of the sear is not hitting the rear edge of the bolt as it comes off the cocking piece. This is more of a problem on the post 64 actions than the pre 64 but does happen. The sear top is to high and hits the bolt edge and stops or drags. To check for this remove the sleeve assemly and then you can function the bolt and see if they are contacting.
To fix, either polish a raduis in the top of the sear to clear the bolt body, or bevel the spot on the rear of the bolt that hits it so it will ride over easier.

Six, check the overall length of the safety plunger. If it is to long then the bolt will drag on the small end of the plunger. To check this remove the sleeve assembly and look on the rear of the bolt for wear marks. Also look at the small end of the plunger that protrudes thru the sleeve by the threads.
To fix, remove the safety lever and take about .010" from the small end of the plunger and reasemble.

It does not sound like lug set back, on a M70 you would feel that when you first try to lift the bolt handle with a fired case in the chamber.

You have to remember that these guns had a lot of hand work to them during assembly, not every on is the same.

Hope this helps.

Jim Wisner
Custom Metalsmith

Does this phenomena occur when you remove the striker assembly from the bolt?

Anyone having over a hundred pre 64 mod 70's
dosen't need any help from anyone. What do you use for a gun safe?.
Good luck!

I don't think you have lug setback. You are experiencing some other sort of mechanical bind. Setback occurs at the fully closed position and you would feel it at the beginning of the bolt lift as the locking lugs were camming out of the recess against the mainspring. Opening the bolt after firing a round would be even more difficult.

Rojelio

quote:

Originally posted by Rojelio:
Setback occurs at the fully closed position and you would feel it at the beginning of the bolt lift as the locking lugs were camming out of the recess against the mainspring. Opening the bolt after firing a round would be even more difficult.

Rojelio

True to a degree, except setbak occurs so gradually that the step or jump is not necessarly abrupt or sharp, there is generally not a step but more of a ramp or slope where because of wear over time from opening the bolt smooths off the step created by the setback so that it gradually increases effort to open the bolt as it is lifted. Very well could also be drag from roughness as mentioned to above. Just my thoughts, I only have 2 pre-64's but have seen frequent setback in guns that tend to be shot with loads at pressures pushing the envelope. it's very easy to see when the barrel is removed or examined with a borescope.

I have seen one mauser action (G33/40 chambered in 257 Roberts) that was set back so badly that the bolt could not be opened, period, without pulling the barrel. That one wasn't gradual at all. Abrupt enough to lock everything up. Other cases may be different.

Rojelio

One of the several BLOWN M70's I have rebuilt over the years, The one that stands out, was a 220 Swift, he had blown the case head, cracked and taken off the RH lug, set back the LH into the reciever about .011" - .012".
So had to recut the locking lug recess, fit a newly machined oversize long bolt to the reciver and then headspace it to the factory barrel.

Had a 30 x 338 in last year with both of the locking lugs broken off. Turns out they had two guns and had gotten the ammo mixed up. This one only set back about .004" so could lap the new bolt in. Then headspace the new bolt to the existing barrel.

I have quite a collection of broken M70 bolts laying in a drawer to show people what not to do.

Jim Wisner
Custom Metalsmith

I agree with that too, When you exceed the envelope with crazy loads setback can happen with one round fired, and they are lucky it dosen't come apart, sometimes obviously they do! Most set back i've witnessed has been the gradual type from continual shooting of loads that are over maximum recommended loads which is quite common with reloaders who try to get that extra few fps, the guys who keep stoking their loads until they see excessive pressure signs and then back off a grain and think they are fine but wonder why their brass only lasts a couple or three loadings.

It’s a very (not simple problem and I’ve seen it many times). As you lift the bolt the bar on the bottom of the cocking piece which engages the main sear and rides in a groove in the rear tang of the receiver. As time goes by the cocking peice sear and the groove in the receiver can wear and the cocking piece over rides the groove in the rear tang of the action causing horribly hard bolt lift when the bolt is half lifted. It can also make it hard to pull the bolt back at full lift. There are two methods of fixing this make another cocking piece from scratch with a wider sear then mill the slot in the action to match. Or, and I prefer this TIG the slot in the action up and re-cut it with an end mill to the proper size so that it can cock properly. It can be worse too. The bolt body can be to small in diameter or the action can be bored to large to the bolt body so that the sear on the cocking piece rides to high. The best recourse for this is to get out the dividing head and make a new cocking piece with a much deeper sear. None of this is cheap! Rod Henrickson

Its gaulding....pull the cocking piece assembly out, the whole thing....Look at the end of the bolt body and you will see a big shallow U type cut that the bolt drags on...yours needs to be hardened...heat it and quench then polish it..

Thanks for all of the helpful responses. The 375 H&H custom rifle I am working on now is one of a comisssion of three rifles made as a set.
A clue as to the problem is the fact that if I lift the bolt on an empty chamber without the sear being set, there is no apparent bind in the same way there is if you cock the action and lift the bolt. In other words, if there was a setback, would you not feel the step up or the bind even with an uncocked action????
I really need to have this one worked on by someone that I can trust to do it right. I don't want to botch it up myself.

quote:

Originally posted by Atkinson:
Its gaulding....pull the cocking piece assembly out, the whole thing....Look at the end of the bolt body and you will see a big shallow U type cut that the bolt drags on...yours needs to be hardened...heat it and quench then polish it..

Ray, I see what you are talking about and there is a pronounced step at the end of the bolt body. There is a flat until you reach the U and then a worn point. Do you take the point down in the polishing? Do you polish it off altogether or what????

I would have to see it to understand what you are talking about...You have the big dip and the the cut for the safety....The main thing is to heat that big dip, quench it to harden and then polish it, just polishing won't cure the problem...I use a copper heat sink, heat it cherry red and dip in in tepid water, then polish..Heat it quick and dip it quick, as you don't want the heat running up the bolt..I hold the bolt in my hand, that way I know where the heat is going.

You mean on the end of the rear of the bolt it worn, yes that needs to be hardened, the whole end of the bolts rear face needs hardening..I have seen a few M-70 that needed this treatment, sometime they did that poorly at the factory and its easy to slip by inspection.

quote:

Originally posted by hawkins:
Anyone having over a hundred pre 64 mod 70's
dosen't need any help from anyone. What do you use for a gun safe?.
Good luck!

I have three and working on four soon it would appear!