I recently purchased a used custom model 70, chambered in .270 Weatherby. Bedding looks fine, barrel looks little used, new Swarovski scope. Accuracy with Weatherby factory ammo in 130 grain TTSX, 140 grain Accubond and 130 grain Norma SP is between 1 1/4"-1 3/4" for 3 shots at 100 yards. I asked a local gunsmith to look the rifle over, and he noticed/blamed the poor accuracy on the bolt jumping when you pull the trigger. He could not tell me what caused the bolt jump, or how that impaired accuracy. I have never heard of this issue, and own 6-8 pre-'64 model 70s, most with very good to excellent accuracy. I see the issue now that I've picked the rifle up, and will check this out with my other pre-64s. Anyone familiar with this happening on these rifles, or others? Is the bolt jump caused by an undersized bolt inside the receiver? Causing the bolt face to not be square at ignition of the primer? or is this negligible and the gunsmith missed something else? all help/ideas are appreciated.

The bolt jump means the handle is set a little too deep. And..yes, I think that can cause accuracy issues. You might try a shim under the handle... just enough to eliminate the jump ...or most of it..you don't want to go the other way.

If that doesn't work, look over the crown...and then...who knows?

Used, pre 64 barrel, in a Weatherby magnum? 1.5 inches is all you are going to get, no matter if the bolt jumps or not. It happens as DW said and is not rare. If you fix that, who knows. But no one can predict accuracy short of shooting it.
I usually look at the dim side of things; that way if it turns out better you will be happy. If not, you won't be surprised.

thanks for the replies. Custom barrel by Lilja, so was hopeful for better accuracy

But you said it looks used. For a Weatherby, depending on if they used the original type free bore, (real long) used can mean bad things.

quote:

Originally posted by dpcd:
But you said it looks used. For a Weatherby, depending on if they used the original type free bore, (real long) used can mean bad things.

Especially if the freebore diameter is a bit oversize.

The 378 and 460 are still .75". Absolute top accuracy can be obtained but loads can be fussy and especially for the 378.

Use heavier (longer) bullets and seat them out as far as prudent.

quote:

Originally posted by Russ Gould:
Use heavier (longer) bullets and seat them out as far as prudent.

The first tw Made in America Mark Vs I had, just after they came out, we Synthetic stocked in 270 Wby and the 375 H&H. Those early ones had all steel two piece bottom metal like the M70.

The 270 Wby was very accurate but what suprised me with that rifle was the 100 grain in Factory and the 100 grain Hornady and 100 grain Speer Hollow Point reloads were the most accurate of the 100, 130 and 150 weights. You just never know. A real rocket with 100 grainers

quote:

Originally posted by Russ Gould:
Use heavier (longer) bullets and seat them out as far as prudent.

If it has a standard SAAMI spec chamber, you can't get a bullet long enough to reach anywhere near the lands. DPCD is correct, if it is a Wby caniber, I won't shoot worth a chit unless you alter the throat area

quote:

Originally posted by Jim Kobe:

quote:

Originally posted by Russ Gould:
Use heavier (longer) bullets and seat them out as far as prudent.

If it has a standard SAAMI spec chamber, you can't get a bullet long enough to reach anywhere near the lands. DPCD is correct, if it is a Wby caniber, I won't shoot worth a chit unless you alter the throat area

I could not agree with that. Actually in relation to its calibre a properly bedded 460 Mark V with a .75" parallel freebore is accurate in the extreme. sk RIP on Big Bores forum.

However, if all else is equal and say we compared a 300 Winchester and 300 Wby and both in accuracy type rifles. The 300 Winchester will be accurate over a wider range of loads. Also, in an all out accuracy type rifle the best load for the 300 Winchester will group a bit smaller. The reason is that altering the seating depth a little bit one way or the ohther alters the ignition and you can't do this with the 300 Wby.

The 300 Wby is also more dependent on consistent neck tension.

On the plus side for the 300 Wby and this is more applicable in hunting style rifles, the 300 Wby is more likely to shoot into the group from a clean cold barrel and alos one that has cold hard fouling in the barrel. The 300 Wby will achieve very good velocities with a wider range of powders and especially those that are a bit fast burning. Pressure spike are less of a problem so the 300 Wby can be loaded to higher pressure.

So for an all out accuracy gun I would pick a 300 Winchester every time. For a hunting style gun I would pick a 300 Wby. Ditto for 7mm Remington and 7mm by and so on.

While the bolt timing issue may be the root cause of your inaccuracy, I kind of doubt it. It can be cured by, as Mr. Wiebe mentioned, raising the bolt handle slightly; with a shim or weld at the root of the handle. If thelocking lugs are vertical when the bolt is closed, one might want to just clear the right side of the cocking notch in the bolt instead. If a person isn't real sure of the cause and effect, he should probably not mess with it.
Another thing which can cause inaccuracy in model 70's is an extractor cut which is too shallow and deflects the bolt when it is closed.
All model 70 bolts are undersized in relation to the receiver and the resultant deflection is probably good for about 5% (at the most) of the vertical dispersion in your groups. I have eliminated all of this slop in the bolts of my model 70 target rifle and, while it may have boosted my confidence, it didn't make enough difference in grouping to get too excited about. When it came to reducing vertical dispersion, the change which had the most effect was the replacement of the striker springs which were, like the operator, old and tired. Regards, Bill.

Cocking piece strikes on the bolt will cause inconsistent ignition. You'll need to remedy that situation, the primers need to be struck the same every single time.
If the barrel looks kind of "used" to naked eye, believe me it's life as an accurate barrel is over, put a scope in it. The life of a rifle barrel is about 2 or 3 seconds considering the bullet travels thru that bore in a millisecond, just something to be aware of, barrels do wear out. At a minimum that barrel is 55 years old chances are good it's been shot enough that it's over the hill.
Barnes bullets are long bullets in order to get the bullet weight up they must be longer. Order your new barrel with a 1-9 twist as a little more spin helps on those longer bullets, stable is always better.
Be sure your Smith is willing to true your receiver and bolt prior to barrel work.

quote:

Originally posted by Timan:
Cocking piece strikes on the bolt will cause inconsistent ignition. You'll need to remedy that situation, the primers need to be struck the same every single time.
If the barrel looks kind of "used" to naked eye, believe me it's life as an accurate barrel is over, put a scope in it. The life of a rifle barrel is about 2 or 3 seconds considering the bullet travels thru that bore in a millisecond, just something to be aware of, barrels do wear out. At a minimum that barrel is 55 years old chances are good it's been shot enough that it's over the hill.
Barnes bullets are long bullets in order to get the bullet weight up they must be longer. Order your new barrel with a 1-9 twist as a little more spin helps on those longer bullets, stable is always better.
Be sure your Smith is willing to true your receiver and bolt prior to barrel work.

The OP mentioned the barrel is a Lilja barrel which appears to be "little used". I take this to mean it does not appear to have been shot much. Regards, Bill

So the bolt jumps when dry fired? Not an issue. The real question; does the bolt jump when live fired? Deaden a primer (oil perhaps), place it in a case, and use it to 'dry' fire and see if your bolt jumps. The forward movement of the striker system will be stopped by the primer. The cocking piece and the firing pin will not hit anything else; no jump. Anyway, try this prior to rebuilding your very fine action!

quote:

The forward movement of the striker system will be stopped by the primer.

Really?

Yes. Really. Firing pin protrusion is usually .040" or more. The indentation on the primer is usually about .025. Measure it.

thanks all for the thoughts and recommendations.

quote:

Originally posted by gwahir:
Yes. Really. Firing pin protrusion is usually .040" or more. The indentation on the primer is usually about .025. Measure it.

I don't know where you get your info, firing pin protrusion is a normally accepted measurement of .055-.065. The depth of firing pin indent you speak of is because the firing effect will push the firing pin back and away from the primer and cause the primer indent to flow toward the firing pin. Try to measure the indent on a fired case after dry firing it.

Where in the hell do you get your info????

Jim: You said it about as I thought it! I also get a little alarmed by a "written word" someone might actually believe it!

Gentlemen, I get my information from measuring. Now, if you can measure a fired primer (not a loaded round) that has an indentation depth any way near the protrusion of the firing pin, I give my most sincere apologies. Talk is cheap.

Stuart Otteson in his book, The Bolt Action Vol 1 has a chapter on ignition of the primer and on firing pin protrusion. My limited observations and comments about the primer stopping the forward movement are completely in line with his observations. He also indicates that primer indentation on a case without bullet or powder usually does not exceed .025" no matter how great the firing pin protrusion. My measurements agree.

In the pre '64 time frame 1 1/2 to 2 inch hunting rifle were good.

Dave

Dave,
The odd thing about "rules of thumb" are the exceptions.
Here is one such exception for you:
My pre 64 M70 Featherweight.308 is a hunting rifle, BUT it has always shot MOA groups and on a good day 1/2 inch 100 yard 3 shot groups. After many outings to make it better, an area bench rest shooter and gunsmith told me "Hell man, those are great groups for a hunting rifle. So save your powder and go hunting" Great advice and I did as he recommended.
I also quit hand loading it, found a commercial brand that shot as well or better than my hand loads and WENT HUNTING. Never looked back.


BTW, my daughter has a Weatherby Mark V Wby 7mm mag that shoots just as well up to a dozen rounds and then the copper must be removed from the barrel to maintain accuracy. We keep the bore clean and she rarely misses.

quote:

Originally posted by nopride2:
In the pre '64 time frame 1 1/2 to 2 inch hunting rifle were good.

Dave

A lot of big game as been and well be killed with rifles the shoot that size groups.

Unless one is shooting out past four hundred yards. nothing more is really needed.

MOst pre 64s Ive owned shot 3 shots into and inch or less, and 5 shots into at least an inch. Most but not all were rebedded or glass bedded, or custom rifles..

Today factory rifles seem to shoot about the same. I recall a lot of custom gun builders, magazome scribes claiming that kind of accuracy was BS, but it wasn't, either they could not shoot or could not work up loads or whatever! Maybe they couldn't build accurate rifles..but it was accepted as common knowledge and it just wasn't right at the time and still isn't. I do believe accuracy is mostly with the barrel, but even some so called bad barrels can be tuned..

ok, so my gunsmith has found and fixed a few problems with rifle parts (replaced extractor collar and firing pin spring), but after all that pin pointed the problem: worn/stripped threads between cocking piece and bolt body allow bolt movement when trigger is pulled. I was advised that unless this is fixed, it was not smart to fire the rifle as a cocking piece flying back into my face would be unpleasant. Anyone seen and corrected this problem? thanks

What? There are no threads that interface the cocking piece to the bolt body.
I would find another gunsmith.

Go back to the top and read the first answer to your post from Duane and find a different gunsmith.

If I remember correctly, the model 70 bolt has a shroud that screws into the back of the bolt. That may be what his smith is referring to.
I have found that it is common that the "shroud locking piece is often under size, allowing the shroud to rotate out of locked position when the rifle is fired. To correct this I had a custom mill cutter made that I use to make replacement keepers. I had two of my three 70 with that problem, and one that was OK. After replacing the two undersize keepers, the shrouds locked in place and don't move without proper pressure.

The shroud can't rotate when or after it is fired, and the bolt opened, whether the lock works or not; that shroud lock is found only on designs with a mid safety position like Springfields, 98 Mausers, and the M70. It only is needed with the safety is in the center position. The bolt sleeve lock is depressed/inactivated when the bolt is closed, as it must be or you could not close or open the bolt. No other design has one, and doesn't need one; the cocking piece holds itself in position by firmly contacting the rear of the bolt.