50-70 300 gr twist rate?

[Malamute]

Im considering using a 50 cal muzzle loader barrel with 1-66 twist to make a Gemmer trapdoor 50-70, will 300 gr bullets work OK in a 1-66 twist? Im a recoil wimp, and it wont be a bear or buffalo gun, so have little need or ability to use heavier bullets, and loads will be light for the most part with an original 1868 action.

[dirtball]

Since you did not say which bullet or what your anticipated velocity will be is hard to guess. But probably you would need about a 48 twist. Go to the link below and plug in your info and it will provide a stability number in red (unstable), yellow (marginal), or green (stable)
GOOD LUCK
Dave

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

[John Boy]

But probably you would need about a 48 twist

48 twist is the 54 cal ML twist ... 66 is 45 cal twist

[Malamute]

Theres a variety of twists in any given bore size depending on if it was for patched round balls, both balls and elongated slugs, or elongated slugs exclusively.

The issue is I found a gun I like a lot, very good original type lines, its a 50 percussion with a 66 twist intended for patched round balls. Im trying to determine if its workable for a Gemmer conversion with the 1868 action I have for 50-70 if I use little short 300 gr bullets.

[dirtball]

Go to the calculator, plug in you bullet diameter, weight, length, then select 66 twist, and play with different velocities. This will give you some idea of what to expect from your proposed project.

Dave

[John in PA]

50 cal 1:66" is roundball twist for black powder velocities. 1:36" probably marginal. 1:25 seems to be most often recommended for .50 cal BPCR

[Malamute]

50 cal 1:66" is roundball twist for black powder velocities. 1:36" probably marginal. 1:25 seems to be most often recommended for .50 cal BPCR

Yes, though most in BPCR shooting seem to tend towards the mid and heavier bullets, Im looking a lighter bullet load that works OK with the 50-70 case and will still shoot OK in a 66 twist. I ran the .490 RB through the calculator at 1700 fps, it said it was marginal stability. A wild guess, a 300 gr 50 cal bullet with approximately 70-75 grains powder may be in the 1300-1400 ish fps range? I may use light smokeless loads, the main objective is make use of the original barrel and my 1868 action to build a well shaped Gemmer type rifle. I cant afford to start over with a new barrel. Ive had the action 20 years or so (and wanted a Gemmer type since the 80s), if I dont do something with it towards the desired Gemmer project I may die of old age before it happens.

[AntiqueSledMan]

Hello Malamute,

I'd say probably not. I do shoot the RCBS 45-300-FN set in a sabot in my Lyman Great Plains Hunter, 1:32 twist.
We've played with others in different rifles, like the LEE 452-200-RF in a sabot in the Lyman Great Plains Rifle, 1:60 twist with good results.
Also the LEE 452-255-RF in a sabot in the Thompson Center Hawken, 1:48 twist with good results.

AntiqueSledMan.

[varsity07840]

The twist in Government .50-70s was 1in 42, which today is considered very slow. Also given that your barrel has a slow patched roundball twist, it probably has relatively deep rifling which is usually not a good idea for BPCR and even worse for smokeless loads. Unless you intend to do the machine work yourself, I'd send the barrel to Bobby Hoyt and have him reline it with a shallow groove, and moderate twist. He can chamber it and cut for the extractor. That's assuming he can also do the square barrel threads. If not find another smith that can do all three. With black powder loads, wouldn't be all that concerned about recoil with say, a 450gr Government bullet. There's no rule that says you have to use 70 gr of powder, hence the 55 gr .45-70 carbine loads.

[Dave T]

Sorry but I don't have any good advice about your choice of barrel, bullet weight, or rifling twist. I do applaud your desire to have a Gemmer style Trap Door. I love the look of those Gemmers and would love to have a Rolling Block in that style, and in 50-70 as well.

If you ever get it built please post pictures, and good luck.

Dave