[Darkker]

That's what I was wondering. What difference does the length of the bullet make?

What twist you need for stability.

Many people say something like:
"For a 68gr bullet, you need an X twist".

The weight of the bullet, is a very minor detail that doesn't matter to any typical reloader. It's the length of the projectile, that needs gyroscopic stability.

Cheers

 

[Darkker]

Hi NC-rifle. Are you measuring the total bullet length or from the O-give?
CJR50

Given his reference to JBM, and the lengths he has listed; those are total lengths.

Cheers

 

[Darkker]

1) So you want to measure the length to know if your rifle will stabilize the bullet. Why not simply get the BC of the box the bullet came in?
2) When I had my 6.5x06 put together I called Hornady asking about the 140grbullet stabilizing in a 1-9 twist, Hornady told me no way. So I called Sierra and asked the same question and they said yes but the 142 gr bullet won't. best shooting bullet in that rifle is the 140gr SMK.
3) I went back and looked at the bullet's he was talking about and as I understand it the 62gr bullet will work in a 223 with factory barrel. maybe that wrong and I don't care. I'd have no use for that heavy a bullet in a 223! I'd rather about the same bullet wt in a 243.

1) Because Stability and BC are not the same thing. As far as the BC is concerned, people classically know a little about the G1. What they rarely care to learn, is that the single G1 number they hold up on a pedestal usually isn't tangible to them. MOST of the time when they are looking at a single G1 for trajectories, they are using it in a cartridge that likely will never appreciably achieve a velocity to be able to achieve that number. They typically are using bullets that are actually more like a G7 projectile, and then get confused why their "expected" trajectories don't match reality.

2) This could likely be for a few reasons. Enviros will change what is or isn't stable, and each bullet(140gr Hornady or 140gr SMK) are different lengths. Since the thread is about a 223, here's a perfect example I posted about years ago. The 75gr Vmax is notably longer than the 77gr SMK. When I would go south and visit friends in AZ, I used to make pretty good money on betting the new agents about shooting milk jugs at distance. Bet them that you can shoot the 77gr and hit the jug at distances, but that they couldn't do that with the lighter 75gr from the same gun. Purely by the numbers, my 9-twist bolt gun would only marginally stabilize the 77gr SMK. But in the hills where we were shooting, they were perfectly stable; the 75gr Vmax were nothing close to stable.

3) The OP does care, clearly. Which 62gr bullet, and what twist a "factory barrel" twist actually is; will give different results. If he wants to go shooting in the winter, and only has a 9-twist barrel. His stability will be marginal, and the BC will be affected because of it.

Cheers

 

[Darkker]

It looks like you're searching for something that doesn't exist.

Back to what MikeG said earlier:
"The same" bullets are made on any number of different machines, which have different states of wear on them. "The same" brand of bullet will have construction changes over time, like the AMP changes on the HornHead bullets.
This is also shown, by virtue of various lengths listed on the JBM site.

Not all "same weight" bullets are secant ogive construction, or even the run the same number of calibers in their nose profiles.
Which is to say, expect to see a lot of various lengths from bullets of a common weight; especially if you're using cheap calipers.


Cheers