Hi Bill.

I am using a 1:24 twist, and after much debate with myself as to whether to go with a .510 or the original .515 groove diameter, decided to go with the .510.

Dave

quote:

Originally posted by loud-n-boomer:
Hi Bill.

I am using a 1:24 twist, and after much debate with myself as to whether to go with a .510 or the original .515 groove diameter, decided to go with the .510.

Dave

Referring to Croft Barker's book, "THE 50-70 SHOOTER'S HANDBOOK" I find you are historically correct even with .510" groove. Pg. 37:

"There are great differences in groove diameters in the 50-70 and, to my certain knowledge, this dimension can vary from .510" to .518". Within my experience I would say that the .50 cliber bullet diameter should be a thousandth under groove diameter to a thousandth over depending on alloy hardness."

1:30 tin/lead (or softer) use .001" smaller than grooves.
1:25 or harder, use .001" greater than groove diameter.

Twists satisfactory for 600-grain bullets:

.50/600-grainer: 1:22, 1-24, 1;26.

The main problem with a 600 grain bullet in a 50-70 is lack of case capacity. 70 grains of black powder--likely less--will be hard pressed to give 1000 fps with a 600 grain bullet. When the bullet weight goes up, the velocity goes down in a hurry with the 50-70. You will be a lot better off using a 1-36 twist and a 450 grain bullet. My 50-70 did pretty good velocity wise with the 515141 Lyman at 435 grains. With the 515142 at 540 grains, not so much. Twist was 1-24. It takes 93 grains of powder to get 1100 fps with a 685 grain bullet in my 50-90. It is not exactly what I would call a flat shooting rifle.

Sharpsguy, 93 grains of powder and a 685-grain bullet sounds like a fairly unpleasant combination in the recoil department.

It is.

My only experience with the big 50s is with a Sharps in .50-90 where I use the 540-grain bullets. In the .50-70, my plan is to go with a flat-nose 450 grain bullet. I will also pbobably try paper-patched bullets in the .50-70. The 1:24 twist is probably faster then I need, and I still have time to change it, but the 1:24 seemed like a good idea at the time. Maybe go to a 1:30 or 1:32?

If I was going to shoot a 450 grain bullet, I would slow it way down. The original shot a 473 grain paper patched bullet or a 450 grain greaser with a 1-36 twist. My 1-24 twist 50-70 was not a good shooter, and that is putting it kindly.

My 1-24 twist 50-90 shoots 6 to 8 inch groups at 100 yards until the bullet weight gets up to 650 grains. Then it shoots 1 1/2 to 2 inches with careful reloads and I make myself live with that. As previously noted, it kicks.

Sharpsguy, thanks for the feedback. Sounds like it wouldn't hurt anything to have the order modified to a 1:36 twist.

Rolling Block original 50-70 twist 1:36".
Trapdoor original 50-70 twist was 1:42" with 450-grain bullet.

1:36" seems to be the twist to use for an RB 50-70 with 450-grainers.
That is about the only bullet weight to consider for a 50-70 ... even the old standard 50-90 loads were mostly for 473-grain paper-patched at 1350 fps.

Mike Venturino's book SHOOTING BUFFALO RIFLES of the OLD WEST pp. 166-167,
has demonstration loads with a Shiloh Sharps .50-90 Sharps 2-1/2":
1:26" twist
.510" groove diameter
30"-long barrel:
The 450-grain Lyman #515141 shot 5" to 6" groups at 100 yards. MV about 1400 fps.
The 546-grain RCBS #50-515FN shot 1.5" to 2" groups at 100 yards. MV about 1300 fps.

Sounds typical.

Pedersoli Sharps 1874 Long Range Target Rifle uses a 1:26" twist on their 50-90 with .504" bore/land diameter (6-grooves) and .512" groove diameter. 34"-long barrel.

Sounds like that Pedersoli could be re-chambered to 50-140 and use 700-grainers.

My old Accu-Load software has a twist rate calculator that plots "optimum twist" for pure lead and pure copper bullets,
with inputs of only bullet diameter and bullet weight:

.512"-diameter bullet:

450-grainer: 51.51" (lead) ... 40.05" (copper)

475-grainer: 48.80" (lead) ... 37.94" (copper)

550-grainer: 42.14" (lead) ... 32.77" (copper)

600-grainer: 38.63" (lead) ... 30.04" (copper)

700-grainer: 33.11" (lead) ... 25.74" (copper)

775-grainer: 29.91" (lead0 ... 23.25" (copper)



http://www.jbmballistics.com/

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Stability Factor (SF) in range of 1.3 to 2.0 is desirable to ensure bullet stability:

.512" bullet diameter
444-grain bullet weight
0.970" bullet length
1100 fps MV
59.0 degrees F
29.92 in Hg
CALCULATED for 1:42" twist: SF = 1.250
CALCULATED for 1:36" twist: SF = 1.701
CALCULATED for 1:24" twist: SF = 3.828
CALCULATED for 1:18" twist: SF = 6.805

50-140 Sharps with 1:26" twist seems to be ideal for 777-grain bullet of 1.562" length:

1100 fps SF = 1.578
1200 fps SF = 1.615
1300 fps SF = 1.659
1400 fps SF = 1.700
1500 fps SF = 1.740
1600 fps SF = 1.777

Rem Hepburn was a 38/40 now a 50/70 all metal being restored .

Nice project,Concho.

quote:

Originally posted by Concho42:
Rem Hepburn was a 38/40 now a 50/70 all metal being restored .

That would give Buffalo Bill Cody the hots for a new girlfriend. Lucretia would get dumped.

And you got to specify the groove and bore diameters, and twist rate for this conversion ... what did you choose?

Barrel is 32 5/8" 1/24" twist , bore .50 , grove is .515 I was told by the fellow who sold the gun to me it was a 1/36 twist , it is not ! I purchased starline brass and RCBS dies for loading and a 500 grain mold lee, also a lyman 515 Gr 515142 Mold . won't know how it shoots till I get all the metal restored and case hardened . A winter project for me summer is for fishing boating Harley riding and trikking down the road to the Chesapeake Bay .