https://www.longrangehunting.c...and-back-thrust.396/

I found this old article surfing around. Interesting comments regarding case design vs back thrust. Safely firing a .30-.30 with the locking lugs removed!

PO Ackley did tests on a 94; but with an IMP case. No locking bolt needed at 40K psi and below. We see that all the time when the primer is protruding; shows that the brass handled all the pressure. I will read the attachment later.

Yes, the article reported that the straighter the case wall, the more it "sticks" to the chamber wall. Of particular note, are comments on the 250-3000 Savage case and how it's taper contributes mightily to back thrust. The AI case much less so as you point out.

quote:

Originally posted by dpcd:
PO Ackley did tests on a 94; but with an IMP case. No locking bolt needed at 40K psi and below. We see that all the time when the primer is protruding; shows that the brass handled all the pressure. I will read the attachment later.

The article also makes reference to brass case thickness and design around this part of the equation.

Some time ago I found an interesting piece on the redesign features of the 7x61 cartridge. I used this cartridge for years during which time Norma made the transition from their original 7x61 S&H case to their new 7x61 Super case which gave an increase of 50fps MV in loaded ammunition with the 160gr bullet. Point made was that the thinner brass was stronger due to heat treating and better metalurgical properties

All of which means nothing; remember that the primer is the weak link here; not the brass.
Remember the "steel head" brass from the 1980s?
This is how we get to use 98K psi in our tank cannons, which are just big Sharps falling blocks. We use steel, electric primers, screwed in. One of my jobs was managing tank ammo. It was like hand loading; ordering cases, projectiles, primers, Propellant, load assemble and pack.

I have a Marlin 336 and a Sav 99 in 25-35 imp.
I wondered about the "weaker" 30-30 case I always used. I formed a few cases out of the much stronger 375 Win cases. Because of the thicker brass, my loads used a couple grains less, but vel before the lever got sticky was the same as with 30-30 brass.

Much to do about nada!

Except...
It is important to remember that lever action rifles don't operate like bolt actions with "pressure signs".
AND if you go beyond allowed pressure, the Marlins and Winchesters do not handle it well. I tend to stick to original factory pressures and mimic factory
loaded cartridges.

The 348 WCF case was one of the best and my favorite over the years. It came about as a strong tapered case derived from the .50 Win Ex.
Even staying within original loading pressures, it has slain bear, deer, elk and my largest moose.
Have an original 99 Savage in 250-3000.
It will still put the original 87 gr bullet out
at 3000 fps, and won't burn out the barrel if
not hot-rodded.

spot on! Like any other rifle design, work up loads a grain at a time, then half gr. to the rifles max, all else is twiddle! Levers are not as strong as a bolt action and they don't need to be..

I did a little informal test some years ago when such things seemed important and a chamber polished to 380 to 400 grt apparently had less back thrust and would allow a tad more pressure than a 600 -800 grt chamber or so it seemed.

quote:

Originally posted by dpcd:
PO Ackley did tests on a 94; but with an IMP case. No locking bolt needed at 40K psi and below. We see that all the time when the primer is protruding; shows that the brass handled all the pressure. I will read the attachment later.

Snake oil, P.O Ackley was selling snake oil. He was selling his wild cat designs in competition to others who had other gimmicks, such as Weatherby,all of which claiming their cartridge went faster because of some special feature. Yes, even tapered cartridges will lock in, depending on the level of friction between case and chamber, up to the point that the pressure in the case stretches the side walls. If you have ever fired a light load, and found the primers above the case head, then you have duplicated Ackley's 30-30 test.





Ackley's choice of a low pressure round was quite "fortuitous". If he had tried a lug less 30-06 AI, the case head would have blown off, and the bolt would have blown out.

When ever Ackley's claims have been put to the test, his claims are proven false.

Experimenting with Bolt Thrust

https://gundigest.com/gear-amm...ing-with-bolt-thrust

Ackley had a bolt thrust test gauge, it is shown in the first Handloader magazine issue. Now, just where is his bolt thrust data? It went in the trash, that is where it went.

Its not snake oil, its physics. The chamber and bolt face combined contain a high pressure explosion, the case is little more than a gasket. With a tapered case the force of the explosion (gunpowder) is concentrated more toward the rear of the chamber and pressure more or less wedges the case toward the bolt face. Or rather the shape of the chamber wedges the pressure toward the bolt face.
With a straight walled case much more of the force is directed outward toward the chamber walls and the wedge effect is virtually eliminated.

I have to say the 250-3000 picks up 300fps over the original case as Ackley stated. that said I never wanted or needed to improve the 250-3000, its beauty is accuracy and the fact that its mild of voice and a sponge of recoil, it kills as well as any caliber Ive used within its ball park, if I want more 25 calber push Id use a 25-06 or 270. I've killed enough elk with the 250-3000 to know if it didn't work it was because someone didn't shoot straight.

OMG! Whenever he who shall remain unnamed (but everyone knows who I mean) chimes in, it's time to change the channel.

quote:

Originally posted by Wstrnhuntr:
Its not snake oil, its physics. The chamber and bolt face combined contain a high pressure explosion, the case is little more than a gasket. With a tapered case the force of the explosion (gunpowder) is concentrated more toward the rear of the chamber and pressure more or less wedges the case toward the bolt face. Or rather the shape of the chamber wedges the pressure toward the bolt face.
With a straight walled case much more of the force is directed outward toward the chamber walls and the wedge effect is virtually eliminated.

Please read up the definition of pressure.

quote:

Originally posted by Peter Connan:

quote:

Originally posted by Wstrnhuntr:
Its not snake oil, its physics. The chamber and bolt face combined contain a high pressure explosion, the case is little more than a gasket. With a tapered case the force of the explosion (gunpowder) is concentrated more toward the rear of the chamber and pressure more or less wedges the case toward the bolt face. Or rather the shape of the chamber wedges the pressure toward the bolt face.
With a straight walled case much more of the force is directed outward toward the chamber walls and the wedge effect is virtually eliminated.

Please read up the definition of pressure.

Your right. My laymens explanation sucked. So I found this for you from; "The physics, chemistry and dynamics of explosions"

"It is well known that limits of detonation of combustible mixtures in chambers depend on the dimensions of the chamber. A detonation propagating past a stationary wall develops a boundary layer on the wall behind the leading shock, and the influence of this boundary layer on the flow can tend to weaken the detonation. For a detonation in a long circular tube of diameter d, the propagation velocity decreases with decreasing values of d, and at a critical diameter, the propagation ceases."

We are not dealing with a static pressure like hydraulic pressure. But rather a dynamic pressure. Tapering the case at the shoulder means the volumetric center of the explosive material is moved toward the bolt face.

I think some are a tad rough on PO, he added a world of information to us at a time when any information at all was available, some of his loads were too hot in some guns just like they are today, so its us to the reader to drop his or anybody's loads and work up, He offered us that information so we didn't have to blow up a gun or two finding a starting load in a world of wildcats and where to start..That is a definite problem and a time and money savor back in the day and is today. I don't know anyone that contributed more to the gun world at that time and place or today for that matter..