I am building a 70-150. The cast bullet weighs 900 gr. The barrel is a pac nor, .705 with 1/20 twist. I would like to have a longer twist. Will 1/20 work ok?

The bullet VELOCITY, LENGTH, and DIAMETER are required to figure out the twist rate. You gave one of them...what is the bullet LENGTH AND VELOCITY???

You can calculate the twist by using any online twist rate calculator if you can supply the bullet length.

I'm guessing somewhere around 0.825" - 0.900"

My twist rate program calculates 1 in 105-110" for a .70" cal, 1500-2000 fs, .900" cast bullet...

1 in 77 for a 1.17" Woodleigh 1000 gr RN SN...1 in 73 for a 1.22" Woodleigh 1000 gr FMJ at 2000 fs.

Luck

You guessed well! .900 length at 1200fps. Pac-nor is the only 70 cal barrel maker I know of and their slowest twist is 1 in 20. Do you think there is any chance it would work with a cast bullet, or is it just too fast?

At 1200 fs I wouldn't worry about it...it is better to overstabilize than go the other way.

The only way to know for sure it to shoot it...there isn't a whole lot of information of any kind out there in the ether, this being almost a figment of Winchesters imagination.

I think my 12GaFH, .73 cal NEF USH has a 1-32 or 1-36 twist, not sure exactly, and I haven't had any problems with bullets/slugs from 500 to 1400 gr with and without sabots, cast, brass and aluminum up to 2000 plus fs.

You might ask/email Ed Hubel, Robgunbuilder, Jeffeosso, RIP or some of the others on the Big Bore forum...there's where the experts live.


What cases are you using, where are you getting them and what rifle/shotgun receiver are you going to use???

WHO's doing your dies???

Why pick the 70 cal instead of a straight 12 ga, (not to be too nosey) where all the pieces and parts are already readily handy???? I though I was the only Weird Harold still floating about.


This one will definitely strain the component availability rope a bit.

Definitely be a conversation starter...hahahahahahahaha

It will have a very high cool factor among the cognoscenti.

Luck

I understand the prototype was on a 1887 shotgun frame, so am using the current reproduction of the same. The object was to duplicate the origional 70-150, so needed to go with .705. I got 12 guage brass from Midway and neck it to .70. I made the dies, and will likely cut the chamber with a boring bar. The mold block was recut with a boring bar from a smaller single cavity ball mold. So far, so good!

That is the same information I came up with...The 1887 shotgun is a neat looking shooter...Hollywood sure likes it. I thought about doing something with one but haven't gotten around toit yet...probably won't...didn't think of the 70-150 cartridge tho', just the 12 ga cartridge and maybe some of James Gates 3" Tri-ball monsters . Definitely has MY little gray cells working overtime.

RMC might should be able to make you some cases with the 70-150 designation imprinted on the case....any length you want.

I tried Magtech 12 ga cases, but wanted more hair so ended up with the blownh out 50 BMG case.

Ed Hubel has done some neat things with the 1887.

You might just start a trend once you work out all the details...I bet lots of Cowboy shooters out there would like one to wave around if it could be produced at a reasonable price. Maybe the 1887's time has come. Who knows.

Keep up the posts as you complete the project, I would like to see the finished shooter.

Luck

well. I got the .705 pacnor barrel and am installing it on the 1887 action. Can anyone suggest a starting load for a 900 gr cast bullet?

How about 150gr of Fg?
That's what Winchester used.

Rich

I would like to use smokeless if I can.

GREAT!!!! Looks like your on your way....

Maybe Ed Hubel has some data on it already at hand...check on the 12GaFH thread.

It should be close to the 12GaFH with consideration to the shorter case...might not need as much fillers.

If I knew the case capacity in grains of water I could run it through my LD program, although for the vey large cases the data results are questionable.

Luck

try 45gr of 5744.

Did you buy some of the window seal round foam yet for filler?

Rich
DRSS

I haven't tried any of the foam fillers in my 12GaFH yet...mostly try to find a plastic shotcup or seal long enough to fill the space or use a fiber filler or use a powder that fills the space.

I've settled on a couple of 750, 880 and 1000 gr hard cast lead slugs and matched things. I use RL17, H4227 and SR4759 for the most part and follow Ed's recipies.

With a 2" case and the length of the 70 cal, 900 gr slug, picking the right powder might not require any fillers.

I'm really looking forward to seeing how this works out for you Gwahir.

Luck

Gentlemen, thanks for the help. The conversion seems to be going quite well. Cutting the chamber and the die with a boring bar worked out. Barrel threads were metric - a bit of a suprise. Working on barrel extractor cuts today. I want it to be a takedown so I can swap between 70-150 and 12ga.

I need to make a swedge die and wonder what size. Barrel is .705. Bullets as cast are .712, so need to squoge them down a bit!

Gentlemen. I had to give up in this idea. See my comments in the 'big bore' section.

Back in the game! I opened up the barrel threads on a large Martini and installed the 70-150 barrel. I fired it twice with pyrodex,80 gr and 100 gr.. The case looks good, although the chamber cut with a boring bar could be more exact. I tried to find 5744 around here, but could not. I am looking for a workable smokeless if there are other options. I am not in love with pyrodex, although it does fill the case nicely.

Sighted in today; 52 gr trail boss and mag primer. There was a little bit of sticky on case extraction, so will back off a couple of grains. I need to do some bench work with it and the lead sled. Recoil is adiquate; like a 3" 12 ga.