Bullet Stability programs

[Wayne S]

Isn't it always the case, one program says yes and another says the bullet needs 2450+ FPS to sabalize:veryconfu
What I have is a 1-10 twist .224 bbl. and and pondering on ordering an
85 gn. .225 mold.

ANY thoughts ??

[Blammer]

I don't think it will work, too slow a twist. I have a 1:9 and the biggest longest Jword I can get to shoot straight is 77gr.

[runfiverun]

the 223 seems to be a cast/speed friendly caliber.
the 2400 fps probably won't be as hard as you think.
but that weight.
if it were jacketed you'd be looking at a 1-8 or a 1-7 twist for stabilization for sure.
and fitting your throat with a boolit that long could be a chore.
if i had to modify the rifle and had never run cast through it before,
i'd pass and opt for a lighter weight that fit my throat better, then shoot for 2800 fps for the fun of it.

[Wayne S]

I don't think it will work, too slow a twist. I have a 1:9 and the biggest longest Jword I can get to shoot straight is 77gr.
What is the length of thoses 77 MK bullets, this 85gn is .864" long[smilie=w:

[82nd airborne]

I think it has alot to do with the barrel. I have a .50 with a 1/12 twist, meant to stabilize the long 650gr api. it will shoot this bullet, amazingly into an inch (centers) but it will also do the same with the stubby 500 gr cast. it shouldnt by reasoning but i have no clue.......

[Doc Highwall]

82nd airborne, your 50 cal has a larger radius giving it greater centrifugal force for stability vs a 22 cal. Wayne S, if you look at the active group buys for the NOE 225-60gr RN you will see what Swede Nelson says about his experience with heavy 22 cal bullets. I am in on this buy for a 1-8" twist Remington 40X.

[Wayne S]

Doc,
for the NOE 55FN or the new 60 RN to work for I want I would have to drive them probably 2500 FPS, AND would need 2.5 MOA @ 200 meters
I'm hoping for that with the 7 Hunter at about 1100 fps or so
OH WELL

[zuke]

How do I enlist my bullet's into one of these program's?
They might learn a thing or two :coffeecom

[Doc Highwall]

Wayne S, I am in on the 7mm Hunter buy for a four cavity that I plan on shooting out of a Encore both hand gun and rifle. I bought one of the NOE 55gr FN and I am in on the NOE 60gr RN also. Right now I am just starting to play with the 311041PB in my 30-30 Win and new dies that I made for my 308 Win.

[grouch]

Greenhill has always been close enough for me.

T = 150 DxD/ L

T = Twist
D = Diameter
L = Bullet length

[HORNET]

Well, the calculator made by Tom Mayer (sp?) at TMT Enterprises says that you'd need 2420 fps to get stability and an old nomograph that I hijacked from the '64 Gun Digest says you'd need about 2700 fps, both based on the .864 boolit length. If that's a .223 case you're going to be pushing it awful hard, might work in a bigger case like a .22-250. IIRC, the NEI 72 grainer was designed to be used in a 10" twist but the recent reports on their quality are not encouraging. Good luck.

OOPS! I forgot to use the derating factor for the boattail on the nomograph. The correct minimum velocity according to it should be 1900 fps.

[Wayne S]

AND the plot thickens, I just received my 14" 1-10 twist Contender BBL in 221 fireball, It came with a target that showed 2" groups @ 220 yds, with 69 gn BTHP bullets at around 2100 fps. This bullet measures .895" long. So much for computer programs. that say this bullet at this speed isn't stable.
Hornet, the negetive comments here about NEi are what has keep me from trying one of their molds, PLUS the cost difference for an LBT isn't that great.

[HORNET]

The fun thing about those BTHP's is that the Effective Length that you're stabilizing is just about from the base to the end of the lead core. The hollow nose length is just kind of along for the ride and to improve the ballistic coefficient (almost no mass). It's a little different with cast HPs of course, where there is significant mass and its mostly near the outer diameter.

[HORNET]

OOPS! Please note velocity correction in post 11. I haven't used that nomograph in a few years and didn't check the notes first. I thought that 2700 looked awful fast... Shucky-darn....

[Eutectic]

The fun thing about those BTHP's is that the Effective Length that you're stabilizing is just about from the base to the end of the lead core. The hollow nose length is just kind of along for the ride and to improve the ballistic coefficient (almost no mass). It's a little different with cast HPs of course, where there is significant mass and its mostly near the outer diameter.

Good info Hornet!

This is why formulas/charts are only 'ballpark' for optimum. As Hornet relates, a .894" length hollow point is a totally different animal than a .894" long round nose soft point. Add a real hollow point (in lieu of the hollow void of jacket with no core) as a cast boolit would have.... another animal appears.

I believe 'center of gravity' or balance point in the projectile's overall length if far more important for optimum twist rate than a generic 'caliber/length' factor. I have had too many cast boolits in borderline twist rates have their accuracy vastly improve by just drilling a big concentric hollow point (on lathe) The 'balance point' is moved towards the base and the boolit reacts as if it were shorter while the micrometer says it's not!

Eutectic

[Wayne Smith]

As implied above, it is the length of the bullet in contact with the bore that should be measured, not the length of the bullet. Enter the wrong data into any formula and you get unreliable results.

[82nd airborne]

Excellent Doc Highwall, I learned something new. It was really baffeling me as to how it could shoot so well with two different bullets. now i know, thanks!