Length of Bullets

[horseman2]

Since mono bullets weigh less, it tweaked my mind to see what the difference in length was.
Barnes 100 grain TTSX .257 was longer than the Hornady 120 grain and the 120 grain Nosler Partition.

Might explain why my 25-06 did not like the Barnes 115 grain bullet.

 

[Ganderite]

Yes. Bullet could be too long for the twist of the barrel.

 

[Workin Man]

Yes. Bullet could be too long for the twist of the barrel.

Is it actually the weight of the bullet that is the main consideration in choosing a bullet weight for a given rate of twist? I have heard that it is actually the length of the bullet that actually contacts the rifling that is main factor. IE a flat based round nose bullet of a given weight will have more contact with the rifling than a bullet of the same weight that is a boat tail spitzer. I am interested in you thoughts on this. Sorry If I sidetracked your thread Horseman2.

Thanks, Jim

 

[todbartell]

for stability - Bullet length is the big factor, not weight

 

[Alpheus]

Is it actually the weight of the bullet that is the main consideration in choosing a bullet weight for a given rate of twist? I have heard that it is actually the length of the bullet that actually contacts the rifling that is main factor. IE a flat based round nose bullet of a given weight will have more contact with the rifling than a bullet of the same weight that is a boat tail spitzer. I am interested in you thoughts on this. Sorry If I sidetracked your thread Horseman2.

Thanks, Jim

The original Greenhill formula only used the bullet's diameter and length. Miller's twist rule formula, which is a simplified version of Greenhills, uses diameter, length and mass.

The length is the overall length of the bullet, the bearing surface length does not matter.

Consider monometal solid copper bullets. They are longer then lead jacketed bullets of the same weight, and therefore require a tighter twist to stabilize. If you worked on bullet mass alone, you can have issues with them.

 

[South Pender]

The two Barnes bullets you mention will be marginally unstable in your 1:10 twist barrel. The two 120-gr. bullets will be fully stable. As others have stated, it is primarily length, not weight, that is determinative of stability.

I imagine everyone on this forum has this already, but if not, here is a useful table of bullet lengths (from JBM Ballistics) for hundreds of bullets by many makers:

https://www.jbmballistics.com/ballistics/lengths/lengths.shtml

Just scroll down to get to the brand of bullet you're interested in.

You can then enter that length (and the diameter, weight, expected MV, and your barrel twist) into the following (also from JBM Ballistics) to determine stability:

https://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

 

[toddpotiphar]

The length is the overall length of the bullet, the bearing surface length does not matter.

If you look at "long-range" bullets you will find very long tapers at both ends of the bullet, leaving much less surface to contact the lands than on a more "traditional" flat-based round-nosed bullet. A longer bullet requires greater stabilization which is imparted by a faster twist. At the opposite end of the spectrum, a lead ball out of a muzzleloader usually shoots best with a twist of 1:60 or 1:72. It doesn't matter what calibre one shoots, the obviously short lead ball does better with a very slow twist. A .32 ball shoots just as well with a slow twist as does a .54 ball, demonstrating that the ratio of bullet-length-to-diameter is the critical factor, not bullet weight itself.