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In answer to some earlier posts, I spent the afternoon at the range with my Shooting Chrony, and got a few recordings. I muffed some rifle readings, in the wind, but my adaptor cartridges made up from 375 H&H virgin brass, held together, and my DIY neck sizer,(no crimp), gave me 2950-3100 readings for 68grs. of IMR 4831 under a Speer 200gr. Hot Core. Since a 220gr. is off of the Powley scale, I also tested one 220gr. Sierra Game King over the same weight of 68grs. of H 1000, and got 2670 fps, with what I believe, looks like to be a very mild load. Note; this is with my test bed rifle, which is an old 29" bbl. BRNO. I'm holding off on any hot rodding until I get my forming-reloading die set from Hornady, later this summer, and make up some real cases from my big Ruger Basics. What will have to wait, is determinng whether the larger diameter powder column of the Ruger (Newton) chambers, will boost the efficiencies of modern powders enough to measure. I'll have to do these tests with the real, high pressure, Ruger Brass. This "cat" of mine, apes the old 8X68S Schuler, with it's streamlined profile, and actually has a longer neck than the Schuler's. My O.A.L. of 3.3", works through my stock mil. magazine. Read; no weakening of the receiver's bottom bolt lug abutment. It's still the same case length as the 375 Ruger, though. I'll get back to this forum in the Fall, and report whether the sharp shoulders of the 375 Ruger, versus my streamlined profile, but with both having the same larger diameter powder column, is what gives the boost that the Big Ruger is showing over the sloping, std. belted mag dia., 375 H&H. I've already necked my fireformed 8mm back up to .375 cal. and to get this trial round to work through the same mil. 3.3" magazine, and crimp into the cannelure of a Speer 285 Grand Slam, I had to trim my dummy case back to 2.5". This trial .375 dummy also feeds really slick, through my tuned up M98, and while technically, I could indeed, have left it at 2.6", like the Ruger, I felt it would be more important to properly crimp the case mouth, into the bullet's cannelure, in a high recoiling rifle. If one did this chop job to a stock 375 Ruger case, I don't think you'd have much neck left. In my wldcat case, starting with a 3/8's inch long neck, and gaining a bit, in necking up from 8mm to .375, I'm still left with a smidge over a .3" neck, after chopping my case back to 2.5", or about what the store bought 375 Ruger starts out with. A Hornady New Dimension 375 Ruger sleeve Seater/crimp die should crimp both of my neck lengths, so I'm shopping around for a quick twist, 1 in 9, cut rifled barrel, or a heavy sporter bbl., M 98 rebore prospect. My adaptor case is 5 grs. H2O less than a virgin Hollands, which is then respectively, 5 grains of H2O less than the 375 Ruger. So; to spin the Grand Slam bullets at the same RPM, from a ten grain of H2O, smaller cartridge case, I figured out that it will take this 1 turn in 9 inch, twist pattern. I also calculated that my 375 caliber variant, is really right there with the 375-358 Norma, which another recent thread discussed. And this big Norma is really a blown out 338 Win Mag. case body. If the wider powder column trumps the sharper shoulders, I may still beat the larger Hollands case in my stock mil. M 98's, magazine length of 3.3". So see ya! down the road in the Fall.
And be sure to realize, that today, I did get at least one, over the top, velocity reading with my Chrono, which could well mean some excessive pressures. I've only got a home brewed neck sizer to work with at present. So this Powley predicted data is only for my own rifle, at this time. In fact, I have slowly worked up to this IMR 68 grain level, so beware!
Thanx Carpooler
 
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