1 / 16 twist, which heavy boolit

[Spokerider]

I have a Uberti Baby Rolling Block carbine that has a 1 in 16 barrel twist.
How heavy of a boolit will it stabilize? I would like to make some sub-sonic rounds for it, and the heavier the boollit the better.

Thanks.

[leftiye]

At least 800 grains, assuming it is a 700*** caliber.

[stubshaft]

Knowing the caliber might help.

[Crawdaddy]

I shoot 463 out of a rifle with a 1:28 twist. I would think bare minimum of 600. Can't imagine you wanting to go that big. I am assuming you are shooting something in the .458 range?

[longbow]

Interestingly enough I am looking at the same sort of idea in .44 mag rifle. I am assuming your Uberti is .45 Colt? If so, I found a design for a heavy for caliber boolit.

I went looking and came up with this Dr. Richard Gunn designed .45 cal boolit in my post here:

http://castboolits.gunloads.com/showthread.php?t=137336

According to the article I found, this boolit is stabilized in 1:16: twist at 900 FPS and so far as I have found in ballistics calculators 1:16" will stabilize even heavier boolits in .44/.45 at subsonic velocities. Still checking and confirming though.

I have scaled it down to .434" but since it is so long for .44 mag brass, I plan to alter the design to a nose bore rider so it will fit into a standard .44 mag chamber and also allow regular weight boolits to be shot without extended jump through the throat. I am all about versatility!

It might be a bit light for .45-70 but is a big hunk of lead for .45 Colt.

If you are interested, I have the dimensions of the Gunn design boolit and will be making drawings of my .44 nose bore rider version as well.

Longbow

[Spokerider]

My bad........sorry.
The Uberti Baby Rolling Block carbine is .357 mag that I have re-chambered to .357 max.

I currently shoot 180gr Cast Performance bullets at 1830 fps with good accuracy. Yes, I know that this is a conservative load for .357 max, but when I decided to rechamber the Uberti carbine, I did so knowing I was probably the first to do so.......

As stated earlier, I'd like to load some sub-sonic rounds with heavy boolits. Not sure how heavy a boolit 1/ 16 twist will stablilize.

Thanks.

[longbow]

Okay then, that makes a difference!

In any case, I scaled down the Gunn designed boolit to .44 and it seems that 1:16" twist is plenty. I suspect it could be scaled to .357" and will also be stabilized. Not sure what weight it will be though.

It would obviously be a custom mould but I can scale the boolit if you are interested.

I have looked up and downloaded some info and software for determining twist rates for my project. These are somewhat more sophisticated than the Greenhill formula or so I understand anyway.

I will take a look and see if they will determine the max boolit weight for you.

Longbow

[gandydancer]

My Tender 357 mag I'm having rechamberd to 357 Max has a 1/16 twist also. I would like this information also. thanks. spokerider. & Longbow. GD

[longbow]

I scaled the Gunn boolit to 0.358" and find it is 228 grs.

According to Wingyro it needs a twist of 1:14.8" to be stable at 1000 to 1100 FPS. Above and below those velocities the stability factor is fine.

It looks as though a flat based version which would be slightly heavier should be good in 1:16" though it would not be as ballistically efficient.

Are you looking at a custom mould or off the shelf? That will make a difference to as to nose shape and boolit length.

In any case, it looks like a flat based version of the Gunn boolit of 230 grs. or a little better should stabilize fine in 1:16" twist with stability factor of 2.01 at 1100 FPS. Not sure how much effect nose shape has yet.

I have some other info on manual calculations but haven't gone through them yet to compare results. Greenhill is easy, these are a little more complicated.

FWIW

Longbow

[Spokerider]

Longbow,
Thank you for doing that research, it helps.

I'm only beginning to look at molds and various designs, as I didn't know what weight of boolit to look at.

Will a flat base .358, wide meplat design of 230gr stabilize as per your info? I would like to load them to approx 900 fps. I do need to stick with the original length of the bullet past the case mouth, as I can just wriggle the max cartridge into the chamber around the rolling blocks as it is.

I had a custom mountain man mold made for me once. It worked well, but I'd rather just find one on here that somebody is selling.

[longbow]

I will take a look but I need an approximate length for the calculation.

I can probably get an estimate from an existing boolit style.

The Gunn Boolit looks a little odd in that the crimp groove is very near the nose. It is supposedly designed for .45 Colt or .45-70 but I think there is too much lead behind the crimp groove for .45 Colt and not necessary for .45-70.

My thinking is that the idea is to reduce case volume by filling it with lead for smaller volume subsonic powder charges. In any case, the idea is good for large volume cartridges and the same idea should work for your .357 Max.

A thought is to get Tom at Accurate Molds to cut you a mould based on this design with whatever changes you need for nose length, weight, etc. If I go ahead with the .44 mag version that is my plan.

Anyway, I will take a look for "standard" boolit designs to see how length is for the calculation and post when I get it sorted out. At worst I can model a WFN in 230 gr. then change length as required.

It appears that the pain base is easier to stabilize so likely a heavier plain base boolit will work in 1:16" than boattail boolit.

How heavy do you want?

What is max nose length beyond the brass?

At some point there won't be room for powder so it will be a trade off on boolit weight and powder volume. I don't know how much powder it takes to get a heavy boolit to 900 FPS.

Longbow

[longbow]

Not sure if you are aware of this but M. D. Smith's reloading pages show .357 Max loaded with up to 255 gr.! I do not see any mention of rifling twist though.

http://www.reloadammo.com/357max.htm

I also found some info on a 230 gr. with nose and OA length so ran that in Wingyro and stability is fine right down to 500 FPS.

Still working on it.

Longbow