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The .375 x 55 Swiss (AKA .375 x .284 Win)
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Old 07-06-2008, 05:04 PM
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Default The .375 x 55 Swiss (AKA .375 x .284 Win)

I got the NEW reamer yeterday, and recut the chamber. Some of you may recall that the first reamer I got was very tight. In fact it was so tight, I am using it as the reamer for making the reloading dies (done ). I am very pleased with the new chamber. I sized (in the new die) 22 .284 Win cases (.284 cases instead of 7.5x55 Swiss cases so I wouldn't have to modify the bolt face/extractor of the Turk action). I fire-formed 5 cases (Bullseye and Cream-of-Wheat) and fired 2 with full charges behind Nosler Accubond 260s. Those 7 cases were used to get precise measurements for QuickLoad (QL).

Based on the QL calculations from the measurements of the fired cases when applying Optimal Barrel Timing theory, I get the following numbers:

Barrel length = 26.0"
Case capacity = 68.86 grains of water
Case capacity with 260-grain Accubond seated 0.637" deep = 51.66 grains of water
Overall Cartridge Length = 2.895"

Optimal Barrel Timing Charge (node #6) = 47.38 grains of Accurate 2495 (100.5% of case capacity)
Estimated Muzzle Velocity = 2388 f/s
Muzzle Energy @ 2388 f/s = 3291 ft-lbs
Estimated Chamber Pressure = 46,985 PSI

Trajectory when sighted in for a 6" target:
.....................................Impact ...... Retained
Range . . . Elevation . . . Velocity . . . . Energy
100 yds . . . 2.9" . . . . . . 2225 f/s . . . 2858 ft-lbs
125 yds . . . 3.0" . . . . . . 2186 f/s . . . 2757 ft-lbs
150 yds . . . 2.6" . . . . . . 2146 f/s . . . 2659 ft-lbs
200 yds . . . 0.3" . . . . . . 2069 f/s . . . 2471 ft-lbs
205 yds . . . 0.0" . . . . . . 2225 f/s . . . 2452 ft-lbs
241 yds . . .-3.0" . . . . . . 2006 f/s . . . 2324 ft-lbs
250 yds . . .-3.9" . . . . . . 1993 f/s . . . 2292 ft-lbs
300 yds . . . 10.1". . . . . . 1918 f/s . . . 2124 ft-lbs

I'm very pleased with these numbers, and based on previous experience, I think QL's numbers will be close. While I'd prefer the 300-yd drop to be 9" or less, for those rare occassions I feel I must take a 300-yds shot, I can add an inch to my hold-over if necessary. Most important to me is the muzzle energy of 3291 ft-lbs, (translates directly to felt recoil), the 300 yd retained energy of 2124 ft-lbs, and the very modest chamber pressure of 47 kPSI - all for something like 47.4 grains of power. 2100+ ft-lbs of energy behind a .375" bullet is gonna take care of anything in NA... without beating me up on my end of the bullet.

Since this is a brand new barrel, and inspection of the fired cases shows that the chamber is as round as I can measure, (zero runout to less than 0.0005"), I am expecting it to shoot pretty straight.

This rifle is built around a Turk .38 action, but once this prokect is complete, (sights, stock, and sighting in), I'm going to make one of my K-31's into a K-31/.375x55. That'll be a sweet rifle if I can figure out how to make the K-31 bolt handle "pretty".

I think I'm going to drill & tap this receiver for 'scope bases. I haven't made up my mind whether I retain a 'scope in the final configuration. I like the looks of open sights, but maybe that 'look' can be for the K-31 version.

Paul
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.375 caliber, .375 swiss, .375x284, wildcat


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