WHY P.O. ACKLEY WENT WITH STRAIGHT CASE WALLSP.O. Ackley demonstrated graphically that up to a certain pressure, the staight walled cases adhere to the chamber wall and literally absorb all of the pressure inside the case during firing. You see evidence of this phenomenon yourself from time to time, but don’t realize what you are seeing. To wit:Ever pick up a .30/30 case fired from an old Win. 94 and noticed the primer backed out a little? Or how about your own reloads? When you start low and work up, ever notice the primers sticking out a little at first, then as increase the powder charge, the primers become flat? If there is any gap between the case head and the breech face, or bolt face, and the pressure is relatively low, as with factory .
30/30’s, here is what happens:Firing pin drives the case forward, pressure builds, case expands and is held by the chamber wall. Gap between head and breech face lets the primer back out, There has to a gap for the primer to back out, meaning the case head must be forward, right?It takes less pressure to move a tapered case back than it does the straight walled cases. Coversely, up to the limit of the strength of the brass, the straight walled cases contain all the pressure. When the pressure exceeds the hold between the case and chamber wall and the case slides back, or the pressure exceeds the strength of the brass and it stretches above the head, allowing the head to move back.
The truth of the matter is that the straight walled cases will contain enough of the pressure load to allow you to operate at pressures well beyond where you ought to be and still get away with it.
Earlier discussion about the standard .219 Zipper reminds me of one I did a few years ago. I started low and worked up in the usual manner and at moderate loadings it only took a slight increase to make the barrel hard to open and extraction difficult. The Zipper has an abnormally tapered case, making it an extreme example. One powder charge and things are ok, next step up, and there’s trouble—-quite dramatically.
Other evidence of the merit of straight walled cases and heavy brass containing the load:When T/C brought out .375 Win. I would have bet anything that it wouldn’t last 6 months on the market before they’d be forced to withdraw it due to frame stretching. But that was before I found out how much stronger the .375. Win case is than its counter parts like .38/55 and .30/30 Winch.Help me out here, guys, I don’t have a book handy, SAAMI max pressure for this round is around 48-50,000 psi, right? This is too much. No? Well why don’t you load your thinner cased .30/30’s to 50,000 psi? Why don’t the books show 50,000 psi .30/30 loads “For the Contender?” Get my drift.
The .30/30’s brass is thinner, point one, and the case has quite a lot of taper to it, point two. The pressures inside the barrel push this case (cork) out the end of the chamber easier than they can thicker walled, staight walled cases (corks).You can run high pressure in the stronger case with the straight side wall. The smaller diameter of he .375 Win case lets one run a little higher pressure than allowable with the .444 Marlin case.
In reality, the .375 Win. case is probably the best or at least one of the best cases to work with———-but everything you can do with the case requires custom dies, except .375 Winchester!So why doesn’t everyone rush out and work their wildcats around this case? I don’t know. Availability? Again, I don’t know. It would make an excellent .35 cal, and would be my case of choice or .30/30 Ackley Imp, which consistent with other comments on the list, is really one the very best cartridges for the Contender. I doubt it can handle the 165’s as well as larger cases, but 110’s through at least 135’s it holds its own pretty well. I haven’t looked at .30/30 Imp data for awhile, but it is pretty much in the same realm as the .300 Savage, and the .300 Savage’s performance is what we are getting from .308 Bellm & .309 JDJ types of wildcats. Again, making a distinction concerning handling the 165 gr. and heavier bullets…………But I’m opening another can of worms ….Hopefully you have a little better picture of the straight walled case issue, and more.