Does the diameter of the case head have an effect on the maximum pressure that the cartridge can safely be loaded to?

Axel

Here we go again.

Review your old posts, Todd

I am not refering to thrust forces. Let me rephrase.

Let's assume one loaded a 30'06 case just to the point the primer blew out, lets assume this equates to 90,000 psi. So we now "know" in this hypothetical situation, that a 90,000 psi load in a 30-06 is, the threshold at which the primer is blown from the case.

Now if one loaded a 460 Weatherby magnum to 90,000 psi would the primer blow out as it did on the 30-06, or would it take less/more pressure to achieve this failure mode with the 460 Weatherby magnum?

Thanks,
Axel

[ 04-21-2003, 19:36: Message edited by: Axel ]

Same.

Stonecreek, are you sure about that? The reason I ask again is, that I have been told that the larger diameter cases can handle significantly greater pressures before primers are blown. I was further told, that due to this "fact" lug shear and/or bolt set back are MUCH more common with the larger diameter cases than with the smaller ones. I was told this by a local gunsmith/dealer. The reason for my question is to validate this gentleman's comment. So please do not take it as a flame.

Axel

With same primers, set in same size pockets, both will handle same pressures, before primers blow,
with same firing pin hole size and firing pin.
Now bigger base cases will cause more setback
on lugs(Assuming same lugs are compared)at same high pressures, due to bigger base size, taking
more thrust.To cause setback or blown primers, takes pressures of course that
no one should load up to all..Ed.

I can get more velocity out of a 9x19mm when hot rodded , than I can out of a hot rodded .357 SIG [357S limitation is primer pocket enlarges and primer falls out].

The bullets are the same, but the diameter of the case around the base of the case are different, and the 357Sig has more case volume.

I suspect this has something to do with hoop stress.

The hoop stress [burst like a banana peel] in a thin walled barrel is:

S=Pr/t

Where S is the stress in psi of tension

P is the chamber pressure in psi

r is radius of the chamber or bore in inches

t is the thickness or the metal in inches

The longitudinal or axial stress [break off like a lizard's tail] is:

S=Pr/[2t]

Because the longitudinal stress is 1/2 of the hoop stress, one can cut

threads on a barrel 1/2 way through the barrel if the receiver supports

Hoop stress for barrels with thick walls and high accuracy we need Lame's formula for maximum stress in a thick walled cylinder subject to internal pressure:

S=P(R2^2 +R1^2)/(R2^2 - R1^2)

Where:
S is the stress in psi of tension

P is the chamber pressure in psi

R1 is radius of the chamber or bore in inches

R2 is radius of the barrel [center to outside] in inches

Clark, what exactly are you saying? Will the 460 Weatherby require less, the same, or more pressure to blow out the primer pocket than a
30-06? Did you get those equations out of your "Machinery Handbook"? If you did I really need to get one of those!

Axel

[ 04-23-2003, 04:51: Message edited by: Axel ]

Clark-That difference is probably brass toughness, hardness, and base thickness.When
developing my wildcat 458 I couldn't get cases
built from Bertram brass to expand primer at really high pressures.But Bell brass would expand pockets at about 25,000 psi lower(About
50,000 psi).

If cases are same quality,same pocket dimensions,
supported by same chamber clearances,same firing
pin and hole,same base thickness and design, same primers they should hold same pressure.The only reason I didn't use Bertram
Brass for the long run was that the sides thinned
to quick from tough base and separated in 8- 14
reloads.The Bell brass at pressures the base handled,loaded 30 to 100 times.New Horneber brass
will be best of both when we get it done.Ed.

I know the 8x57mm limit, when I increase powder, is the brass flows, which causes the bolt to stick.

The same action in 45acp [which is thin wall brass compared to rifle brass], when I increase powder, limits out with sticky bolt and primer falling out at the same load.

This leads me to believe that rifle brass is overbuilt, but still just brass. It starts to move like toothpaste at 70 kpsi.

I know a guy that made steel case heads that screws into cases. I think Casull had the same thing on his web site for a while.

I did some experiments with making 10mm brass from 30-30 brass, and found the 10mm case design was already optimized in a pressure - capacity trade off.

My guess is for the 30-06 that higher velocities would be had with thinner brass and more powder or even better, steel case heads and more powder.

What may make me wrong about that is the time domain. I know when I overload Bullseye powder in 357 mag, the cases stick. When I overload H110 with the same bullet, the primers get beat up. The H110 is slower, and can get through the delay line of the flash hole. The Bullseye has a higher peak pressure and can push out the case walls harder. If rifle brass is thicker, because it has a longer pressure time, then there may be no advantage to making it thinner.

If one made 30-06 cases with 45acp brass and brass tubing, one could find out.

[ 04-23-2003, 07:57: Message edited by: Clark ]

I can't help on the large end. But the cartridges I've made based upon the 25ACP case necked to 22 for rifle use showed that a small increase in rim diameter resulted in a greater capacity to hold primers. Granted, much of this could have had something to do with the amount of clearance around the rim in the bolt face. When I started my 22 Epperson Cricket project I tried to turn the rims to 22LR rim dimensions, after blowing a few primers I ended up leaving them alone and had much better results.

This may or may not help...just my experience.

I have stretched primer pockets in Norma brass with loads that did not damage either Remington or Winchester cases (7X57mm). I believe that reason was that the Norma brass was softer, because the case capacities of the Norma and Winchester brass were the same, while the Remington cases held LESS powder than the other two.

[ 04-23-2003, 18:54: Message edited by: eldeguello ]

Would it be safe to say that none of you have loaded up a Rigby based cartridge to HIGH pressures? I am in the process of building a big bore and have been told that these Rigby based cartridgers can shear off lugs prior to blowing out primers so I am somewhat concerned with an accidental overload during load development.

Clark, using the thick walled cyclinder equation, which is what the head of a cartridge case, I have the following stress for a 30-06 loaded to 90,000 psi:

1021 MPa

To achieve this level of stress in the 460 Weatherby magnum case:

Requires a chamber pressure of: 105,800 psi!

So according to YOUR equation it should take more pressure to blow the primer out of a 460 Weatherby magnum than a 30-06! This assumes of course that the brass is equal between the two cartridges.

Axel

[ 04-24-2003, 00:13: Message edited by: Axel ]

Weatherby cases are just Rigbys with a belt, and they are loaded to relatively high pressures,
and don't shear off the lugs.ed.

For a given area, pressure will give exactly the same force exerted in any shape, whether it is a star, egg or sphere.

Primers are roughly the same size, so they will experience the same force for a given pressure (the primer). To get a primer to blow out, or for the primer pocket to enlarge would be a function of the pressure exerted over the whole case head since it is the head moving around that is leading to the enlargement. A larger case head would experience more force on it due to area. But rememeber the primer pocket and its abutment are the same size (area) in a large rifle primer.

I agree with Hubel that it is brass hardness/thickness that is coming into the situation that will affect pocket enlargement.

Axel,
The reason a primer gets blown from a case has nothing to do with the primer. The fault lies with the design of the case. Lets use the .30-30, .30-06 and a .300 Wbty. too illustrate this. All three use the same size, large rifle, primers. Yet all three function at different pressures. The design of the cases determines the safety pressure point where the case starts to expand to a point where it will no longer hold the primer. The thickness of the web area of the case, coupled with case body thickness determines this safety point. Pressures are limited by the ductility of brass. The brass case will always be the weak point in the rifle-cartridge combination. I hope that this is of some help. Good luck.