Alf,

I am glad we can discuss this! I really would not want to get into a fight with you over something as relatively insignificant as to how to model internal ballistics.

I haven't read those articles. Am I understanding you correctly that they are available from the University of Michigan Library? If so a trip to Ann Arbor may be in order.

With regard to achieving the closest possible pressure estimate relative to reality, I think John got that one when he suggested using a strain gage on Ron's rifle.

ASS_CLOWN

Very interesting ...

AC,
I too was turned off of the "Load From a Disk" type programs by seeing them predict high pressures and low velocities in many loads that I had firsthand, longterm, utterly safe satisfaction with.

28 years ago, I completed 108 credits of the 120 required for a BS in chemical engineering, before stumbling off to medical school. Now the math and science related to your modeling is beyond me. RIP, amen.

Please consider these generalities for the non-existant average .404 Jeffery pressure barrel:

Part 1:
*********************************************

GIVEN: 80 grains of RL-15 produced 49,800 psi (~50K psi) with a 400 grain conventional jacketed RNSP.

GIVEN: Varget is usually accepted to be just a tiny bit slower than RL-15, but very close in burn rate.

ASSUME: 81 grains of Varget produces 50,000 psi with a 400 grain Woodleigh RNSP.

So, if I wish to increase the pressure of the Varget load to 60,000 psi, what powder charge increase in Varget will give a 60,000/50,000 or 1.2 fold increase in pressure?

Assuming a linear function through out the range would this not be 1.2 x 81 grains = 97.2 grains?

Of course 85 grains is the 100% density load, with this bullet, so would that produce 85/81 x (50,000 psi) = 52,469 psi?

This would indeed mean that Varget is utterly safe in the .404 Jeffery with noncompressed loads.

Of course this does not match your model, which seems to predict about a 10% increase in pressure for a 5% increase in powder charge. Is this anything like a 2.00 throttle factor for a bottlenecked cartridge? To make it fit your model would 85 grains of Varget give 54,938 psi with the 400 grain Woodleigh RNSP? Then 89.1 grains of Varget would give 60,000 psi?

Part 2:
***********************************************

How does bullet weight alone affect pressures with a given charge, all else being equal.

For example, ignoring barrel friction differences, what will the pressure be with a 340 grain bullet fired with the same charge (81 grains) that produced 50,000 psi with the 400 grain bullet?

All this is hypothetical, and I would appreciate any help. At this point, I do not want to complicate things with velocity, which is so variable from gun to gun, and so too would be pressures.

Just ASSUMING the average .404 Jeffery pressure barrel.

Thanks.

The A-Square RL-15 pressure data matches AC's model in this regard:

400 grain Dead Tough RNSP
72 grains RL-15 >>> 41,000 PSI
76 grains RL-15 >>> 43,600 PSI
80 grains RL-15 >>> 49,800 PSI

10% increase in powder charge causes a 20% increase in pressure, very accurate over this range.

So ???
400 grain Woodleigh RNSP
81 grains Varget >>> 50,000 PSI
85 grains Varget >>> 54,938 PSI

I say my 87.6 grain load of Varget with the 340 grain North Fork is well below 60,000 PSI.

Safe. Heck, it is probably less than 58,000 psi, just like AC predicts.

And considering my non-fouling Magic McGowen barrel, the pressure is probably less than 55Kpsi, with the African Sheep Bullet by North Fork, 340 grains at 2700 fps.

Probably.

Likely.

Maybe.

Almost assuredly.

Magic.

quote:

Originally posted by lawndart:
Probably.

Likely.

Maybe.

Almost assuredly.

Magic.

SWAG

Buy a donkey, as Elvis says in RSA.

Alf,

The peak chamber pressure I came up with that will yield the 404 Jeffery case head are:

Using the following data:

Case head ID = 0.49"
Web thickness = 0.115"

C26000 H04 (minimum tensile yield strength = 63,000 psi)
C26000 H02 (minimum tensile yield strength = 52,000 psi)

The primary failure mode would be the web, which should manifest itself as extractor marks.

Pressure to initiate web yield:
C26000 H04 (@ min yield strength) ~ 83,000 psi
C26000 H02 (@ min yield strength) ~ 68,800 psi

Pressure to initiate primer pocket yield:
C26000 H04 (@ min yield strength) ~ 115,000 psi
C26000 H02 (@ min yield strength) ~ 96,000 psi

If I understand the slang correctly.

C26000 H01 is quarter hard
C26000 H02 is half hard
C26000 H04 is full hard
C26000 H06 is spring hard

Most case heads I have measured hardness on fall within the H04 and into the lower H06 range.

So what does all this mean. Simply put, one would need to be using some REALLY CHEAP CRAPPY brass to see any 'pressure' signs in 404 Jeffery brass until they were into the 70 ksi range. With quality brass their rifle may become the fuse (meaning the rifle may fail first).

My chamber pressure calculations are based off of three dimensional (triaxial) combines stress analysis based upon the von Mises theory of combined strain. This technique combines the affects of the principal stresses (stress in the X, Y, and Z axes) with the shear stresses acting in each shear plane (there are 6 of them in three dimensions). So we are looking at radial, longitudinal, and hoop stresses, as well as, shear and 'bending' stresses.

I look forward to seeing what you come up with for maximum chamber pressures. Please provide some information as to the nature of the stress calculation methodology utilized.

ASS_CLOWN

Does anybody have any references to throttle factor for bottle-necked cartridges, or is AC the only one who knows about this?

AC,
Does the pressure generated by a given powder charge increase linearly with the bullet weight (all other factors such as bore friction artificially kept constant), or some other order of function?

Help me out here please, as I am struggling, and I don't think you are BS-ing .

Using the "RIP-throttle" factor, I get 58,148 psi for the 400 grain Woodleigh with 87.6 grains of Varget.

Assume this to be true, please, for the sake of discussion.

What does your model say that the pressure would be if we just switched the bullet to a 350 grain Woodlweigh?

RIP I don't know the answer on these questions on the linear nature of increase in bullet weight. A more important question is as you increase powder charge is it linear. I think this is a resounding NO. As you approach the maximum pressure for the matearials it increases exponentially and is very unstable. One round within safe range but just barely and the next may be over(as in WAY over). At least that is my understanding of how it works. Good luck. D

D Hunter,
Thanks for the input. I know things go exponential at some point. However, within the range of Varget I have worked with, the velocities were a nice linear progression of about 30 fps increase for each grain of powder increase, using the 340 grain North fork.

The A-Square actual measured pressure data with RL-15 seems to show a nice linear increase in pressure and velocity with their 400 grain Dead Tough.

A 10% increase in powder increased pressure 20%.
When do these lines of different slope become exponential, or am I just looking at the flat part of a parabola (or second order function) beside a straight line.

Obviously the powder charges are a limited domain of useful case capacity, and things will get squirrely with heavily compressed charges or half empty cases.