Our 10x25mm Revolver project was spawned during a chat over adult beverages between myself, Mike Hastings, and Sam Hotton. Sam in particular is a fancier of fine single-action revolvers...Our fantasy was a modern, RIMMED .40 cal. cartridge, which using either .40 S&W or 10mm jacketed or .38-40 cast bullets. It would serve the medium game “packing pistol” role, approximating .38-40 black powder rifle ballistics with smokeless, from a sturdy revolver, in a smaller, sturdy case, formed from common brass, avoiding the excess free airspace and fragile nature of .38-40 brass. A case full of black powder or Trail Boss would be adequate for Cowboy Action, plinking, or small game at about 700 fps with either round ball or bullet.
The .44 Russian case...when necked down to .40 has a capacity of 20-21 grains of 3Fg, 4.0-4.5 grains of Trail Boss or 14 grs. of IMR4227, filling the case to the neck-shoulder junction "gently, without compression" using the RCBS Little Dandy Rotor #18. Using the RCBS Little Dandy Rotor #20 a charge of 16 grains of IMR4227 is compressed 1/16" with the 40-252H at 1.50" OAL.
From our custom 5-inch Ruger Blackhawks, smokeless performance with Bullseye powder exceeds .40 S&W factory ballistics. With “magnum” pistol powders it shows promise to produce a powerful hunting load approximating the 10mm Auto. We attained 1000 fps with Accurate 40-182H and 950 fps with 40-220H cast bullets with 5 grains of Bullseye. With 7.4 grains of Auto Comp we got 1140 fps with the 180-gr. and 1080 fps with the 220-grain cast bullets. Indeed an adequate “packing pistol...”
Dave Manson made our reamer...John Taylor...rebarrelled our Rugers using a Green Mountain “gunsmith special” 10mm barrel with 16” twist, rechambering one cylinder for each gun to .40 S&W, and the other to 10x25mm. .
Source brass...is...Starline .44 Russian, which we neck down and use as-is, resulting in a 0.970-0.975” case. The shoulder angle is 6 degrees, 48 minutes Basic, the same as the .38-40 Winchester. Case body diameter is .454" at the shoulder, the same as the .38-40 and .457" at the base, and the same as the .44 Special.
“DougGuy” in North Carolina made our loading dies by cutting down and honing out .38-40 Lee dies on his Sunnen hone... Doug’s firm price to modify your set of LEE .38-40 dies to 10x25mmR is $150. You supply Lee .38-40 dies, Doug does the mod, and returns your dies insured in small flat rate box. A shortened Lee Quik-Trim case holder, to cut .44 Specials, costs a bit extra.
The die alteration process is as follows:
1) FL sizer and seater are both cut off by 0.4" and a new thread relief is turned.
2) Neck portion of the sizer die is honed inside up to .420" diameter to produce a tight and correct fit for loading .400” jacketed bullets, without expanding, but flaring only.
3) Neck portion of the seater die is honed inside to .429" diameter and the ball seat of the seater die is honed up to .402", because if it is tighter, then it really needs to be.
4) IF you want to cut down .44 Special cases, Doug can shorten a Lee .44 Special case holder for the Quik-Trim, by cutting 0.16" off the top. Then you adjust the Quik-Trim to cut the necked down .44 Special cases to 1.000+0.000/-0.005"
5) Once you have fire-formed brass, it is possible to neck-size only by using a 0.525” spacer with your .40 S&W Auto dies.
...Starline .44 Russian brass comes 0.0960-0.965" long. After necking down to .40 cal. they will be 0.970-0.975"...
We elected NOT to get an inside neck reaming die made to thin our case necks. This saved a great deal of money in development costs and case making effort. It also results in a more sturdy case which can withstand rough handling, unlike paper-thin .38-40s!..
Based on feedback Dave Manson revised the chamber neck diameter on the print and anyone ordering this reamer in the future should specify .40/.44 Special Short Harris Rev1-6/18...with... .429” neck diameter, having a .402” cylindrical ball seat 0.10” long with 6 degrees, Basic forcing cone...
10x25mm loads in Starline .44 Russian brass with 180 Hornady FMJ, Accurate 40-182H and 40-220H, again, all with 5 grains of Bullseye. The 180-grain Hornady FMJ with 5 grains of Bullseye give 932 fps with a standard deviation of 15 fps over a six-shot string. Accurate 40-182H with the same 5 grains of Bullseye in the 10x25 gave 1009 fps, an Sd of 10 fps and shot to the sights at 25 yards, just like it did in the .40 S&W. The 40-220H gave 949 fps with a standard deviation of 10 fps and grouped at the top edge of the black on a B15 25-yard timed and rapid-fire pistol target. Indeed, about right for a 100-yard zero. Both groups very slightly left, maybe one click to center them up.
Next step was to test the same RCBS Little Dandy #9 rotor which meters 5 grains of Bullseye, but this time metering 7.4 grains of AutoComp. The 40-182H gave 1138 with a 10 round Sd of 14 fps, and 40-220H gave 1083 fps with a 10-round Sd of 11 and round groups.
The RCBS Little Dandy #18 rotor which fills the case to the neck-shoulder junction, without compression, was used to meter 14 grains of IMR4227. Velocity was 1033 fps with an Sd of 16 with the 40-182H bullet and 1008 with an Sd of 12 with 40-220H, with significant unburned powder and loose groups. IMR4227 is too slow for the light bullets, but might work with heavier ones. UPDATE Dec. 24, 2018 - Little Dandy Rotor #20 meters 16 grains of IMR4227, filling the case up the neck enough to permit slight compression when the heavier 40-252H bullet is seated. - Will try in the Ruger First, STAY TUNED!
A dip measure made from a .357 Magnum case measures about 20-21 grains of Goex 3Fg or 4.2-4.5 grains of Trail Boss, filling the case “gently to the shoulder without compression.”
The maximum black powder charge is 24 grains using a drop tube or compression die. Sam’s recommended 4.5 grains of Trail Boss is a “full charge” load, with 4.8 grains being the “absolute full stop not to be exceeded,” because Trail Boss should NOT be compressed!
I tried lighter charges with Bullseye and Accurate 40-220H and 40-224H, looking to find a low recoil load of traditional black powder velocity level, approximating the .41 Long Colt. 3.5 grains of Bullseye in the 10x25 case, with 40-220H gave 760 fps with a standard deviation of only 7 fps and an extreme spread of 29 fps over a 12-shot string. Substituting the 40-224H ogival wadcutter results were almost identical with 748 fps, an Sd of 7 and a 12-round ES of 23 fps., producing satisfying 2-1/2” groups at 25 yds.
73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia