A lot of lengths are here, how accurate he is I'm not sure. He has the Hornady 100gr .257 at .987".
https://www.jbmballistics.com/ballistics/lengths/lengths.shtml

He shows the Sierra 100gr Pro-Hunter at .97".. still a bit long. The Sierra 90gr HPBT GameKing is .89", that would shoot well. They claim it's a high-velocity varmint bullet, but works well on medium game at 250-3000 velocities. ????


Originally Posted by gnoahhh
Something I've been pondering, Rory, is length of bearing surface in relation to overall length of the bullet in this application. I wonder if a .25 bullet that's theoretically short enough to stabilize but has an inordinately long bearing surface (think, say, a 100+ grain bullet with a very blunt round nose and not much of an ogive) would or wouldn't stabilize. Someone asked me that recently, maybe Joe, and I couldn't come up with a definitive answer.
What I've read is that it's almost purely about overall length. The bullet is stablized in the barrel - it's stuck in there nice and tight and moving (almost) perfectly straight. The question will be whether it will be aerodynamically stable - and the physics there is apparently all about overall length, spin rate and velocity.

Alfred Greenhill's formula, which is rough but works pretty well: (C x D(2)) / L = T.
C == 180 for > 2800fps, a constant
D == diameter of bullet
L == Length of bullet
T == Resulting twist needed to stablize it.

So.. solving for T = 14, you get an ideal bullet length for a 1-14" twist of 0.85". The farther you wander away from 0.85", the less stable/accurate it will be. Keith posted a chart of bullet lengths and velocities and how well they'll stabilize, that's a great resource to reference.

When we played with those 100gr Partitions - original length was 1.04" - far too long to stabilize. Got 7'-8" groups. Cutting the lead nose off shortened them to 0.915" - and they stablized quite well with decent groups. Yours that were shortened to 0.85" appeared to stablize even better. From the 2nd line of Keith's chart, you can see we went from deep red with the original Partition to greenish-yellow with mine, to probably green with yours.

Originally Posted by KeithNyst
It seems as though our discussion on twist usually is on the .250-3000, so I put this chart together to show the Miller Bullet Stability Factor for 0.257" bullets to show the impact of barrel twist. The intent being to see how sensitive the .250-3000 stability is to actual production barrel twist variability.

I used 3000fps for the 87 grain and 2800fps for 100 grain. The 87 grain bullet is the Speer Hot-Cor; the first column for 100 grain is the Remington Core-Lokt.

I varied the twist and made calculations for 87gr and 100gr bullets

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