May I throw out a possibility/opinion?

The forces on the side wall of a cartridge is equal to the force of the powder burning in the case (pressure) times the area of the case wall times the coefficient of friction. In a pistol case the walls are roughly cylindrical and normally short. It's easily possible that the force resisting the push to the case head is easily over powered by the thrust against the case head.....but in a rifle cartridge the number of square inches of case wall and the resulting pressure is greatly increased.....thus a rifle will have a much greater propensity to stick to the chamber. This can account for the semiauto functioning of a Rimfire.
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Further.....when the pressure builds in a rifle cartridge such that the case head is pushed to the bolt face and then against the action, the case has stretched as much as it's allowed by the headspace available to it. When this happens the force of stretching the brass has become history and the resulting force against the bolt is equal to the pressure times the number of square inches of the internal case. The friction forces only slightly delaying the bolt thrust but not in any way eventually diminishing it!

As an example.....a .30-06 at 58,000 PSI and an internal case diameter of .443 (.473-.030) has an area of .154 square inches and a resulting bolt thrust of about 9,000 pounds. This so overwhelmingly over powers the case web and causes it to stretch that after the metal has stretched it no longer has any restraining force against the thrust on the bolt therefore surface finish in the chamber of a high pressure rifle is not relevant to the issue of bolt thrust. It may have relevance to how much the case stretches.....

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On the question about by "CRF" issue with strength of an action.

It's well understood that the weak link in any firearm is the brass case. Further when we have actually seen brass extruded from the actual case head (in the case I mentioned in a push feed M-70) about .050 deep by .19 wide into the extractor cut and then stopped only when the extractor was wedged tightly against the inside of the receiver ring, we can easily understand the value of fully supporting the entire case including the case head during the firing process. CRF rifles do not do this.....in the case of my Mausers almost half the case head is open to rupture. Same for my M-70 rifles in CRF.

Until recently, I have not seen a M-700 blown up (it was clained to be from too small a charge) and the one M-70 push feed I saw blown up I did explain....but I don't think anyone bought it.

I've been fascinated by blown up rifles all my life and far and away the largest group of blown actions were M-70 pre-64 and M-98 Mausers.....and also it seemed to me that most of them were chambered to .257 Roberts, .264 Win Mag and .270 Win.....no scientific study.....merely a thing of memory....and does not prove anything.

I offer this as It was asked why my comments on the strength of CRF rifles. It really has little to do with massive strength....it has more to do with surrounding the case with enough steel.

Try to imagin why most metals have different yield and rupturestrength.
If your way of looking at the brass starting stretshing(yielding) suddently loos all strength, then there is a rupture.
A rupture often occures after gradually exceeding the yield strength, gradualy elongating the stressarea, ending up with a rupture. All the way up to rupture the metal will carry minimum the yield strength. Brass is known to have a verry high elongation %, That is the reason why it is so easy to shape, by coldforming. All the coldforming is performed above the yieldstrength, within the elongation %, below the rupture strength.


The statistic reason for seeing mutch more crf blow up, is logically caused by the fact that they blow up at lower presure.
Statistically higher presure is more seldom than lower presure. So the rate of blowups must be counterproportional with the presure needed to create a blowup

quote:

Originally posted by jørgen:
Try to imagin why most metals have different yield and rupturestrength.
If your way of looking at the brass starting stretshing(yielding) suddently loos all strength, then there is a rupture.
A rupture often occures after gradually exceeding the yield strength, gradualy elongating the stressarea, ending up with a rupture. All the way up to rupture the metal will carry minimum the yield strength. Brass is known to have a verry high elongation %, That is the reason why it is so easy to shape, by coldforming. All the coldforming is performed above the yieldstrength, within the elongation %, below the rupture strength.

jørgen,
I always appreciate your posts as they contribute to the subject.....and they are from an engineering mind.....this isn't unusual for good gunmakers but your posts are especially interesting.

Thanks for that....I'll mull it around for a time.
Vapo

jørgen,
I'm going to agree with you.....you have twisted my arm...

If the web thickness is .015....lets say .030 and the diameter is .473 then the area of brass that is in force is 3.14159 X .473 X .03= .044 square inches.....if the yield strength is 40,000 PSI then the amount of bolt thrust held by the case is 1800 pounds. This is a long ways from a significant amount of force compared to the 9,000 pounds of pressure against the inner case head.

What say you?

Brass is elastic and will start to stretch at relatively low levels of force. I made up a split chamber (in 30/40 Krag). I chambered it so that about 1/2 inch (12.75 mm) protruded from my chamber. I was able to insert a piece of brass and clamp the chambein my barrel vice to lock the brass into the chamber. I set up a dial gauge mounted on the chamber piece and contacting the case head. I found that I could exert enough force, by hand ( I used a rod, with a tee handle, inserted through to the base of the brass), to deflect the case head .002". I doubt that I can exert any more than a couple hundred pounds of force yet I could deflect the case head by a measurable amount. In a front locking action, the bolt face doesn't deflect anything like .002"; probably more like .0005" at normal pressures. I am, therefor, convinced that whatever strength the brass lends to the bolt thrust equation is a drop in the bucket. Now, if the rifle has enough headspace that the brass must stretch right to it's elastic limit before contacting the bolt face, it's plain it could potentially reduce bolt thrust by a significant margin. If, however, the headspace was sufficient and the pressure was sufficient to exceed the elastic limit of the brass, then the brass would fail and the contribution of the brass would be zilch.
If the pressure was not suficient to overcome the brass' elastic limit, the brass would not contact the bolt face and bolt thrust would be only what was transferred through the protruding primer cup.
Higher pressure leaves less brass available to stretch since more of the case is adhereing to the chamber wall under pressure. Therefor, the brass will stretch less before failing but will take more pressure to stretch at all.
In the end, if there is no head clearance, the brass will not add to the strength of the action until pressures are sufficient that the boltface is deflected by more than .002 or so. At this point, the pressure may be high enough that the brass flows so, again, it is taken out of the mix. Regards, Bill.