Question about Bullet Lengths


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GinSlinger
January 17, 2003, 04:13 PM
So I ran the calculations. Shooting .270 out of a 1:9 at 3000fps I am supposed to be using a 1.215" long bullet. Okay, this is longer than what I am shooting right now (Winchester Power Point). Now to my question: Is there any way to find out the bullet length for various bullets without resorting to opening every brand/make and measuring? The bullet manufactures websites don't have that information. My loading manuels don't have that information. So I may be stuck measuring bullets unless one of you guys can help.

Just for double check I am using the following formula:
T=C(K/(L/C))
Where:
T=twist rate (9)
C=caliber (.277)
K=Constant (180)
L=Bullet length (solving for)

Anyone used this method? Does it work? I am at my wits end trying to find a good bullet powder combo w/o too much trial and error. I figure if I can whittle it down to two bullets and two or three powders I'll be doing well. Incidentally, I am shooting a Savage with a 22" barrel.

Thanks ever so much,
GinSlinger

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Frohickey
January 17, 2003, 05:24 PM
Couldn't you just ask the bullet manufacturer via email?

Thing like this is not easily answered since there are a lot of bullet profiles.
Spire points are a conical shape after the bullet shank.
Spitzer are -6S, and there are -7S and even -5S bullet ojive shapes (http://www.corbins.com/design.htm#top), and all of that affects bullet length.

From Corbin's website:The standard rifle ogive in spitzer (tangential ogives) is 6-S. It provides the best all-around compromise between weight range and ballistic coefficient. As the nose becomes more pointed and thus longer, the efficiency of the bullet at overcoming air resistance tends to go up. But at the same time, the bullet becomes longer and, with the same density of core, requires more rifle spin rate to stabilize. Eventually, a bullet can be made so long in the ogive that it is not practical, because too much spin is needed and the velocity is reduced more than the efficiency is increased. Obviously, you cannot shoot a bullet down a rifled bore that has rifling approaching circles or screw threads, and expect the bullet to follow the twist instead of tear across it. But this is what is happening when you try to increase the rifling twist too much, in an effort to stabilize very long bullets.

GinSlinger
January 17, 2003, 06:23 PM
I assumed that the formula was for overall length. I found the same formula on several websites when looking for the ideal bullet weight for my gun. The formula was based on a formula from a Brit from many years ago (don't remember details--geting older?). Basically this formula was presented to show that weight wasn't the determining factor for twist performance, but rather the length. This went contrary to everything I had been told (that certain twists perform better with certain bullet WEIGHTS). I had planned to use H-4831 & H1000 which are compressed loads when pushed near max. Perhaps I should just drop the concept of bullet length and just go with 110 & 130 gr bullets from manufactures I trust??

As a side, with compressed loads are flat-based preferable to boat-tails? Or would either work equally?

Once again thanks,

GinSlinger

Frohickey
January 17, 2003, 09:02 PM
I think boattails only lend themselves when you are going for long range shooting, and need a bit more velocity at that range.

With the boat-tail, you have less turbulence at the rear of the bullet, and have a much streamlined air path. But that only matters at long ranges when bullet flight time is long.

Art Eatman
January 17, 2003, 09:41 PM
The reason folks talk about faster twist for heavier bullets is that in general heavier bullets are longer, right? The thing is, the much-longer ogives are a more recent phenomenon, mostly intended for the long-range target shooters. Most hunting bullets are either spire-pointed or use the shorter ogive.

Most .270s are set up with a twist to stabilize for 130- and 150-grain bullets, since those are the most commonly used. Possibly some are a bit fast for 100-grain; I don't know.

Years ago, I loaded with a caseful of the old surplus 4831 that Hogdon got his start in selling. Fill it up, seat the bullet. (I think that old surplus 4831 was a wee bit slower than what's available today, but I wouldn't swear to it.) Back then, I didn't measure the OAL; I just compared it with a factory load and called it good. :) You learn...Anyway, I don't even remember if anybody made a .277 boattail in 1964.

Many people work up loads with the bullet seated as far out as possible without hanging in the rifling--and that will feed through the magazine. Helps to be a bit cautious for pressure signs, of course. Probably no problem in a .270 with 4831. A compressed caseful is barely max--used to be so, anyway.

FWIW, Art

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