Starting a Big Bore Subsonic Rifle - need some input

[daviscustom]

Not sure which forum this fits in.....but this started life as a factory rifle so here goes.

I need some input from the cast boolit experts on a rifle I am getting ready to build. It will be chambered in 50 Hushpuppy (.510 cal bullet in a 7 wsm case cut at the shoulder). I am using a Savage Axis action for the build and I need input on the proper twist rate to use for cast boolits. The subsonic round uses 50 bmg bullets for jacketed projectiles....and that is what originally got my attention, along with the availability of pulled surplus bullets for cheap. After the glitz faded from the big jacketed bullets, I realized that they are just going to plow through what ever they hit and never have any chance of expansion or transferring much energy to the target in a hunting situation.

I have always assumed that I would experiment with casting BIG boolits for this rifle, but now that has become my primary interest..... to the point that I wonder if I am making a mistake by choosing a fast twist barrel (1:10 twist) that would be the standard choice for heavy jacketed bullets fired at subsonic velocities (about 1000 fps). It has been suggested that for lead I should be getting a slower twist. My plan is to be casting 600-800+ grn boolits for this rifle, so that is the first thing I need input on.....what twist will stabilize these big pills and not strip the sides off the bullet in the rifling?

This will be a short barrel, only around 17", and as you may have guessed (being a subsonic round) it will be a suppressed rifle.

My interest in bullet designs will be in maximum energy transfer to the target along with designs that will maximize long range (300 yard ballpark or more hopefully) accuracy. The more aerodynamic the better but looking at flat points, hollow points, and hollow points designed to carry a small jacketed bullet to force expansion.

Any input is welcome.

[rhbrink]

Do you have an idea of about how long these boolits will be and I assume .510 diameter?

RB

[daviscustom]

Haven't found any options in the size I want yet, so just a guess based on a 750 grn A-max......around 1.5-1.75" long.

Yes .510

[felix]

I would go 24 twist and be done with it for your subsonic requirements in a 50 cal. Reasoning is based upon the stock 45-70 twist of 22 for 405-500 boolits. If you are scared to use that, go to 18 twist for 500 grainers at a 1000 yards for optimum wind bucking. Because your diameter far exceeds 458, up the twist back to 20-22. That should be enough twist for your 1000 fps muzzle, 1000 yard target. ... felix

[Nobade]

Standard 50 BMG barrels are 1:15, that will stabilize any reasonable cast boolit you want to use up to 900gr. easy.

I have a friend here in Abq. that built one of those, but he goes the other way to see how fast it'll go. He used a Pac-Nor 50 BMG barrel and it works great. The spotter/tracer bullets are a lot of fun as long as it's not fire season. They can be shot to very LONG distances and you know when they get there. It also works well with lighter, say 400gr. or so, pure lead paper patched boolits for killing things. Basically works like a rimless 500 S&W.

[daviscustom]

So you agree that 1:10 twist will be nothing but a headache for cast boolits?

I was wondering if going with a standard twist for something like a 50-70 might be a reasonable choice....even though the velocity was higher.

Didn't see that last post.....I had wondered if a standard 1:15 for BMG might be a happy medium.



Hmmmm the only consensus thus far is that 1:10 is too fast for lead.

Nobade: what kind of accuracy is he getting with large lead boolits, do you know?

[rockrat]

1-15" twist will be good up to at least 2200fps with an 850gr. I have run it as slow as 1000fps with decent accuracy.

100yds@2200fps

[longbow]

Maybe there is some useful info here or at least people you can contact for specific questions:

http://castboolits.gunloads.com/show...ight=hushpuppy
http://castboolits.gunloads.com/show...ight=hushpuppy

Longbow

[daviscustom]

Longbow: Unfortunately Aaron/ 82 Airborne has been off the grid for several months....no info from him for quite a while. He is the one that got me interested in this project.

Looking at the Mountain Molds website, their bullet mold program shows a recommended twist of 1:26 for 600 grn and 1:18 for 900 grn.....probably not going that big though......1:20 for 800 grn

I know with jacketed ammo the thought tends towards faster twists for lower velocities

Rockrat do think a slower twist then 1:15 would be better/worse accuracy wise?.......and what sizes are those boolits.....and who makes the molds?

When you say "decent" what are we talking?

[rhbrink]

I did some checking on my program and came up with these numbers. These are only suggestions to give you a idea of where to start your mile age may vary.

All velocities were 1000fps, a boolit weighting 500 grains at 1.25 inches long up to a 750 grain boolit 1.75 inches long would stablize very well in a 20 to 22 inch twist.

Just noticed that you are in central Missouri I live over in Cass county?

RB

[daviscustom]

Thanks for the info, I'm in Saline county....near Marshall.

[Idaho Sharpshooter]

Ever heard of the Greenhill Formula...?

[daviscustom]

Nope, but I'll do a search.

[nanuk]

seat a shortened Jword backwards and you'll have a close range sledge hammer!
cut it off like Johnson (?) did with the 50 alaskan

[MT Chambers]

Have you checked out the trajectory of those bullets at around 1000fps? Your .22 rimfire will shoot flatter to 200 yds., but this may be okay for you. Drop at all ranges will be more then the old Black Powder cartridges, even the 50/70.

[daviscustom]

I've been rolling it around with the guy who is going to do the barrel work for me and he thinks I want to stick with 1:10 twist because of the low velocity. He says the bullet won't be going fast enough to strip the sides off and for the 850 grn cast boolit I'm leaning towards now.... I'm going to need a lot of twist to keep a 1.79" long projectile stabilized. he plans to shoot cast in his as well, and he is actually thinking about a 1:8 twist.

I found a Millers formula twist rate calculator and it is recommending 1:20.....just a slight difference in opinion. http://bulletin.accurateshooter.com/...and-stability/

[rhbrink]

I've used the Miller formula a lot and it seems to be very accurate at least in my experience. Let him build his with a 8 to 10 inch twist and build yours with a 20" it's your money. It'll be interesting in seeing which one shoots best I'm betting on the 20 inch twist. Keep us posted on developements.

RB