Author Topic: FredM needed... (Read 434 times)

Donaldo · « **on:** December 31, 2004, 05:10:13 PM »

Here's the situation. Berger 224 dia 75 grn VLD bullet, length, 1.050". Berger says it needs a 1/9 twist barrel to stabilize. They don't say what velocity. Stability is dependent on velocity and twist, right? I would assume a certain rpm to be stable. Question.... What velocity is needed out of a 1/9 barrel and what velocity out of a 1/12 barrel is needed to stabilize this bullet. Muzzle velocity only please. Seems I used to be able to figure this, but can't seem to get my mind around it now. Thanks in advance.

cheatermk3 · « **Reply #1 on:** January 01, 2005, 04:27:11 AM »

A 1 in 9 twist is 1.33 times faster than a 1-in-12 twist, so it would seem that, for whatever velocity your bullet is stabilised in the 1/9 barrel, you will need 1.33 times that velocity to get that same RPS in a 1-in-12 twist tube.

If this is correct, for a load that produces 3000 fps MV in your 1/9 twist barrel, you will need 4000fps to produce the same RPS, in a 1/12.

I don't think it's quite that simple, since it seems to me that if the reason a faster twist is needed is that the longer, heavier bullet has a greater tendancy to tumble, due in part to it's greater mass in the ass, so to speak, the faster you push it, the more faster it must spin in order to stabilize.

What caliber are you talking about?
EDIT: I've been known to make a mistake or two especially with fractions. Hopefully Fred M will be along shortly to correct any errors I have made here.

Fred M · « **Reply #2 on:** January 01, 2005, 05:50:10 PM »

Doaldo.
It is doubtful that you can push a bullet of this weight and length fast enough to overcome a 3" twist disadvantage. If you did I think the bullet would come apart.

These bullets were originally designed for the military (75and 80gr) to give the wee guns more range and more Ft/lbs. These bullets are only good in 223 or 22BR or others of its type. which many target shooters now use out to 1000 yards. A 223 powder charge is about all the 224 bore can handle with good accury in mind and of course minmal recoil. GI-Joe is very sensitive to recoil.

How fast you have to drive one of these bullet to be stable in a 1-12" twist.
would require complete parameters of the bullet which I don't have. I would think you would need a case of a 300 Win Mag at a pressure I would not want to sit behind, to reach about 4500 ft to stabilize this bullet in a 1-12" twist that is the best I can do, is guesss.

When Walt Berger says 1-9 twist he is not kidding, because he knows who is using his bullet and for what reason. They work well past 300 yards punching paper and stay in the x-ring. One moa will do fine. I think.
Sorry I could not help.

Donaldo · « **Reply #3 on:** January 01, 2005, 06:11:50 PM »

FredM, Thanks anyway. Near as I can find out the 75 grn VLD needs about 2900 fps to be stable out of a 1/9 twist barrel. Maybe a bit less. Anyway to convert this to a 1/12? Other than the 1.33 times factor as above? Just bought a box of these, they are pretty little things. Look a lot like a needle. I have a 1/9 barrel on order for my Savage 110. We shall see....