While looking at some old Fraser sporting rifles I notice some step down from the breech shoulder rather quickly, a la featherweight configuration, to a cylindrical section. What is the minimum safe diameter this section can be for a 257 Roberts cartridge loaded to +P pressures.

Winchester Model 70 Featherweight contour; not saying that it couldn't be thinner; it can; look at some double rifles and drillings. But for a bolt action, it is also balance that is important. Col Whelen turned a Springfield barrel down to 1/8th inch wall thickness at the breech; fired it with no problems and finally cracked it with some proof loads, and that was not even with chrome moly steel.
So, there is a few times safety factor in barrels. They are not made to minimum safe specs.

The thing I always laugh at is when people insist on making the chamber area 1.25" or so in diameter and claim it is for safety reasons. Does it never occur to them that the threads at the root are a good deal smaller?

Funny; I have had that said to me as well and I tell them to remain quiet and calm whilst I explain it to them. . Then they say, well, the receiver will hold the barrel thread expansion when you fire it. To which I then tell them to quit talking and go away because they are too dumb to own a rifle.

I admit my ignorance, but hope I'm not too dumb to own a rifle.
Is there any difference in strength and ability to handle pressure among a large ring Mauser with small thread barrel, large ring Mauser with large thread barrel and a large ring Mauser with an integrally milled barrel, assuming same steel and the same overall dimensions.
If so please explain.

Ability to handle pressure in the barrel has nothing to do with the receiver. So, the only difference is the diameter of the barrel threads; in your example, .980 vs 1.1 inch. I don't put magnums on small threads, but some do. It is usually the WSM fat cases that can cause issues in small diameter barrels. The receiver does not help the barrel contain pressure until it is way too late and bad things are happening.
Not sure what a Mauser with an integrally milled barrel is.

A Mauser with integrally milled barrel doesn't exist to my knowledge. Only used to expand on the point. I know Savage made some 22's in which the receiver and bbl. were all milled as one piece - the bbl. didn't screw into the receiver. Not sure that one of their early high powers (models 20, 45) weren't made the same way but I could easily be wrong.]
Following is a quote from Remington's safety and strength features - "Finally, the last “ring of steel” refers to the fact that the barrel is threaded into the receiver, which was machined from hardened steel."
I believe Browning A bolts have a thread diameter of only .935" - less than small ring Mauser. Are they not as strong as most actions which have larger diameter bbl threads even though offered in wsm?
So, if the receiver ring provides no additional strength, can you explain why it doesn't (so that even a dumb person can understand)?

This is what I am asking about. SR receiver, likely ~1.1"dia.shank then reduced to what diameter. Less than .900 maybe.
https://imgur.com/SBDKAxJ

Sorry, tried to post a picture and failed. Help!

I suspect the Fraser bbl pictures is similar to the Win M70 Featherweight contour. The actual thread diameter is smaller than the initial bbl. stepdown. If you look at Douglas barrel website you can see a diagram of the featherweight bbl that is the same or very similar to M70.

Right, it looks to be about like the M70, in which the threads are one inch and the taper starts at .960.
Are Brownings as strong as any? Sure; that shows just how strong chrome moly steel really is.
Do you really want your barrel to expand and be supported by some fairly coarse and often loose, threads that only contact the receiver in a few random places when you fire it? No.
Remington's three rings of steel all contribute zero to the radial pressure produced during firing. They only come into place when you blow up the case head. The first ring is the bolt face, the second is the barrel surrounding the bolt head, and the third is the receiver ring. None of which actually hold Radial firing pressure. By the time all of the 3 rings come into play and do their jobs, the entire rifle is ruined beyond reclamation. But the system does work; I have seen two blown up with pistol powder.

Remember, all the rifles we use were designed when steel was in it's early years and alloy steel as we know it now did not exist. Nickel steel was the newest thing in the late 1800s.

quote:

Do you really want your barrel to expand and be supported by some fairly coarse and often loose, threads that only contact the receiver in a few random places when you fire it? No

I agree, but if threads are well fitted, and I presume some are, why why doesn't the surrounding receiver provide some additional strength?
I agree chrome moly barrels have tremendous strength, but if, as you say, the receiver provides no strength, then why would one need to be cautious in a small ring Mauser rebarreled with a modern chrome moly barrel?

Due to the Axial pressure component, not the Radial. Some small ring Mausers have the thread relief cut so deep that the ring is very thin between the threads and the locking lug recess. The receiver does, indeed, take all the axial thrust produce from firing, (minus the brass to chamber adhesion component,, which, with dry brass and chamber, can be as much as 40K psi) but the receiver needs to be able to handle all possible back thrust, which can be in the 8000 pound range.
Radial thrust, OTOH, is completely contained by the barrel; it can't rely on receiver threads to absorb pressure as those can be very loose.
Of course, the receiver would take pressure, but only after the barrel was expanded and stretched.

Thanks. Not to belabor a point, but can't the threads be fitted and tight?

Consider this; the M2 BMG (50 BMG) barrels are screwed into and out of the barrel extension in order to adjust headspace, and they are not torqued at all; they are held in place by a little flat spring. If they expanded into the barrel extension each time they were fired, it would be impossible to adjust them. We need an engineer to explain plastic deformation of steel and modulus of elasticity to us as it applies to barrels.

Can't the threads be fitted tight? Custom ones are usually fitted as tightly as good machining practice allows, but even if you lapped each one in, what would you accomplish? Factory ones are fairly loose. You are still limited in chamber pressure by the brass case.
Another thought; our M256 Tank Cannon operates at close to 100K PSI, and the barrels are not torqued in, nor are the threads tight; they are held in by a nut against the recoil mechanism.
How? Steel cases and screwed in primers.
So, using the receiver as a pressure vessel would accomplish nothing.

quote:

Originally posted by dpcd:
Winchester Model 70 Featherweight contour; not saying that it couldn't be thinner; it can; look at some double rifles and drillings. But for a bolt action, it is also balance that is important. Col Whelen turned a Springfield barrel down to 1/8th inch wall thickness at the breech; fired it with no problems and finally cracked it with some proof loads, and that was not even with chrome moly steel.
So, there is a few times safety factor in barrels. They are not made to minimum safe specs.

dpcd,

Major Julian Hatcher turned down an 03 barrel to 1/8 inch (.125") wall thickness and it held regular and high pressure cartridges with no visible results. He then turned it down to 1/16 inch (.0625") thick over the chamber and it held 3 regular service cartridges perfectly. He then fired a 75,000 pound high pressure test cartridge which blew a piece out of the side. See Pages 201 & 202 of Hatcher's Notebook for photos and his description.

But I agree, barrels are not made to the minimum safe dimensions, not by a long shot.

And in their defense, barrel/firearms manufacturers have no way of knowing what kind of crazy-hot handloads someone may try to fire.

Can't speak to bolt guns as I'm a double guy. For double rifles I have a minimum of .180" around the chambers and down to .085" at muzzle. I've seen a certain Italian gun with .065" muzzle thickness on a 9.3x74r.

SAMMI +P pressure for the Roberts is listed @ 58000psi. Would approximately .225 chamber wall be adequate to allow safely shooting +P loads.

The receiver threads do hypothetically contribute to hoop strength in the barrel extension. The problem is that this added strength only comes into play at the very last instant before the metal begins to move permanently in the barrel. But by the time the hoop expansion in the chamber begins to load onto the receiver thread, you have already suffered permanent damage to the chamber. Yes, the hoop strength in the receiver could prevent some personal injury when things do eventually let go, but it won't prevent damage to the firearm.

I suppose in theory there is a magic point where you could add (JUST A LITTLE BIT MORE PRESSURE) and the receiver would prevent damage. But creeping up to that a pound at a time and having such a tiny amount of strength gain is like arguing how many angels can dance on the head of a pin.

Sorry; I attributed that Springfield test to Whelen when I should have said Hatcher. I certainly have Hatchers notebook but was typing from memory; point is the same.
Yes, as I said, the receiver only contributes to radial strength AFTER the barrel has already exceeded it's elastic deformation stage and bad things are rapidly happening; and all that is long after the brass case has failed. I have never seen a modern barrel crack open at the breech end.
Read what Mr Little said; if you saw the breeches of some double rifles you would be scared if all you had seen was bolt actions.

Mr KDA, the Winchester 70 FW shank is .960 OD in front of the chamber, and that gives a wall thickness of .265, which its also the same wall thickness over the one inch threads. (tapered brass case you know) That is why Winchester derived those numbers to be the same. Arbitrary? Maybe.
Don't go thinner than that. Why? Because I can't tell you to do something I have not done. Will it blow open and kill you at .225 wall thickness? Is it a modern chrome moly barrel?

quote:

Originally posted by dpcd:
Read what Mr Little said; if you saw the breeches of some double rifles you would be scared if all you had seen was bolt actions.

Somewhere, someone, years back, perhaps Pat McManus or maybe Jim Carmichael back when he was writing Just Jim, did kind of a shtick on the evolution of blowing ones self up.

It all started off with black powder shooters which made pipe bombs to shoot lead bullets and they generally used low pressure explosives and cheap steel and basically put their nose's over it, prayed to whatever boogy they prescribed to and touched it off.

Later came better steels and breach loaders so they invented a higher pressure explosive to bring back the excitement, prayed to whatever boogy they prescribed to and touched it off.

After that, they invented the bolt action rifle which pushed the chamber and main blast area 6 inches further away from their face and prayed to whatever boogy they prescribed to and touched it off.

Finally today, we have the pistol shooters which dropped the pressures down to 6th of what they used to be and hold them WWWAA A A A Y Y Y y y y . . . . . . out there and touch it off.

The general consensus is that, the shooters of today seem to have lost their faith in their gods or have become atheists.

dpcd, yes modern chrome moly barrel. Just looking at the picture of the link I posted and doing the math I am having a hard time convincing myself the barrel dia. is .960 just past the radius shoulder given the chamfer on the leading edge of the action ring + likely some grinding of the ring to remove any markings. Could be just perspective is messing with me.

I am just telling you what the Winchester Model 70 FW barrel dimensions are. . What yours are, you will have to measure for yourself.

quote:

Originally posted by kda55:
This is what I am asking about. SR receiver, likely ~1.1"dia.shank then reduced to what diameter. Less than .900 maybe.
https://imgur.com/SBDKAxJ

kda55,

Looks like .900" or less to me, too.

Are you able to shoehorn a .257 Roberts in to that Kurz M98?

Very nice little rifle, BTW.

Mexican Mauser

quote:

Originally posted by kda55:
Mexican Mauser

Huh...

The Fraser photo that you posted the link for looks like an Original Kurz to me.

But you are apparently talking about a different rifle.

Anyway, I have a .250 Savage on a shortened SR M98 that measures exactly .900" O.D. over the chamber. I've used it with factory loads with no issues for almost 20 years. But those loads do not operate at 58,000 PSI.

I'm asking due to action ring diameter only, not length. Are all Mauser SR not 1.3" dia. The photo is merely an example of a small ring action and the barrel diameter over the chamber area, do not know the caliber.

Yes they are 1.3 inches OD, but that alone, is not what is important. after all, many bolt action receivers are 1.3 inches in diameter as well.

Interesting thread. Hatcher's experiment is not really well known, but the results are basically that an 30-06 (or similar sized) case is safe with a barrel wall thickness of .125", way below what anyone would consider minimum.

I remember way back when no one would chamber the big Weatherby cartridges (378 & up) in a Ruger No. 1 because the wall thickness to the thread bottom would be only about .175 (give or take a few thousandths).

Now there are plenty of these around including some in the Lazzeroni cartridges which run above 60,000 psi. I have never heard of one failure.