In looking over my .50/70 Sharps data, I came accross the Formula for determining minimum rifling twists.
: As my 1859 Sharps relined barrel has the slow 42" twist bullet mould modification was required to maintain resonable weight, yet shoot accurately in the slow twist.
: FORMUAL: bullet length in inches divided by the diameter in inches = 'X' which is divided by 150 = 'X' which is multiplied by the diameter in inches = twist in inches required. As stated earlier, this "Twist" should be reduced by 1" or 2" to get an even more stable bullet.
; Expamples: - Lyman mould # 515141 casts the original type bullet for both the .50/70 and the .50/90 Sharps. It is a pointed, grooved lubricated bullet with square grease grooves, with a diameter of .515" and is .950" long. According to the formula, it needs a twist of 40.3" or SHARPER for best accuracy.
: As my rifle's twist is 42", a bit slow, by at least 2", I shortened the mould by boring the nose and hard silver soldering in a rouded top plug. The mould now casts a cup-point bullet of 420gr. weight fo 1/2:1/2 Wheel Weights and pure lead fo a length of .830" which by the formula requires a twist of 47.4", well within the capabilities of this rifle.
: Subsequent testing of this bullet shows full BP loads, as well as Herco smokeless loads with buffer material, to shoot into less than 1.3" at 50yds, just a ragged hole for 5 shots and 1.45" at 100yards, also a single hole group, hand-held on the bags. The shortened bullet was a definite success in this rather slow rifling.
: The full length bullet shot resonably accurately, however as we've seen with the 48" twist buttoned TC barrels, it may not be stable once it strikes a large game animal. My best accuracy with the pointy original bullet ran 6 shots in 3.26"X 3.12" at 100meters, with 4 of those in a snug 1.565". This was with the original battle sights, blade front and "V" notch adjustable rear. The barrel is 22" long. Straight from the mold 520gr. Lyman bullets were tipping at 25yds, and whistled down-range when shot at the further bunker.
: The heavy bullet Lyman #515142 mould, casts a bullet of 520gr. and requires a minimul twist of 36.0" for stability.
: My only testing with BlackMag3 powder showed a load of 75gr. weight gave a velocity of 1,400fps with the 420gr. cup-point bullet. The recoil was quite heavy in this light-weight carbine.
: Other testing with Herco lists 21.0gr. and Kapok filler as giving 1,260fps, which should do for a nice shooting hunting load. It went 1.1" for a 3 shot group at 100meters.
: 44.0gr. 3031 and the 420gr. listed at 1,307fps.
: All of the above were shot in blown-out .348Winchester brass. It's only detriment is the extractor has to be manually held in, so the slightly smaller rim won't slip by. Extraction is desisive, just as if using Dixie .50/70 brass.
: A final thought, is that most bullet will shoot accurately and maintain stability with very much faster twists, but the reverse doesn't work. In other words, the full sized 450gr. Lyman bullet for the .50 will shoot very accurately down to about a 20" twist, but at 42", becomes unstable, as shown by slightly oblong bullet holes in a 100 meter target.