Newbie Looking For Advice... 270 or 308

[Xtremetj]

Mathematically, a 9 twist with the 140 VLD at 2950'sec is stable at sea level in zero degree air but it is getting on the low end. That said, stable is stable. Is 1.11SG optimum? No. Is it adequate? Yes. At 5000' elevation and 60 degrees the SG is over 1.5.

I'm new to all this terminology. Is a SG over 1.5 better or worse than 1.11?

 

[MudRunner2005]

I'm new to all this terminology. Is a SG over 1.5 better or worse than 1.11?

An SG of 1.5 or greater, is considered fully stabilized.

A 1.11 SG would be unstable.

 

[Michael Eichele]

An SG of 1.5 or greater, is considered fully stabilized.

A 1.11 SG would be unstable.

1.11 is stable. Stable is stable. Anything above 1.0 is stable.

While there maybe more yaw in the beginning with 1.11 versus a 1.5 SG (and it will last a bit further downrange), it will eventually settle down. As a general rule, a bullet's stability will increase over time until it gets knocked around by the effects of it nearing the subsonic range and transitioning into the subsonic zone. Some bullets will survive it and some wont and the list of factors that determine this is long and complicated but the fact that it started out with a 1.5 SG or 2.0 for that matter doesn't automatically mean it will survive the transition.

SG is for 'Gyroscopic Stability'

What a hunter doesn't want is to develop a load in the summer at high altitude that is stable on the lower end of the spectrum and then go somewhere at low elevation in cold temps only to find that it isn't stable there. For example, you could live at 5000' and develop a 210ABLR in a 12x barrel during the summer at 60 degrees which will yield about a 1.3 SG which is more than adequate. Then, go to sea level in 0 degrees and the SG is under 1.0 which is completely unstable. Personally, I live and shoot less than 100' above sea level and do much of my development in the winter. If I'm punching clean round holes at 100 and 300 yards, I know that any hunt I will be on I will have adequate stability. I have found by trying to push the edge of twists using heavier bullets that when it is mathematically around that 1.0 mark, bullets keyhole at 100 yards.

 

[MudRunner2005]

1.11 is stable. Stable is stable. Anything above 1.0 is stable.

While there maybe more yaw in the beginning with 1.11 versus a 1.5 SG (and it will last a bit further downrange), it will eventually settle down. As a general rule, a bullet's stability will increase over time until it gets knocked around by the effects of it nearing the subsonic range and transitioning into the subsonic zone. Some bullets will survive it and some wont and the list of factors that determine this is long and complicated but the fact that it started out with a 1.5 SG or 2.0 for that matter doesn't automatically mean it will survive the transition.

SG is for 'Gyroscopic Stability'

What a hunter doesn't want is to develop a load in the summer at high altitude that is stable on the lower end of the spectrum and then go somewhere at low elevation in cold temps only to find that it isn't stable there. For example, you could live at 5000' and develop a 210ABLR in a 12x barrel during the summer at 60 degrees which will yield about a 1.3 SG which is more than adequate. Then, go to sea level in 0 degrees and the SG is under 1.0 which is completely unstable. Personally, I live and shoot less than 100' above sea level and do much of my development in the winter. If I'm punching clean round holes at 100 and 300 yards, I know that any hunt I will be on I will have adequate stability. I have found by trying to push the edge of twists using heavier bullets that when it is mathematically around that 1.0 mark, bullets keyhole at 100 yards.

We must be talking about the same thing, but with different scales... According to Berger's stability calculator, 1.5 or greater is stable. Less than 1.5 is marginally stable. And I'm not sure where their scale drops off to unstable, but that's how their stability calculator is setup.

 

[Michael Eichele]

We must be talking about the same thing, but with different scales... According to Berger's stability calculator, 1.5 or greater is stable. Less than 1.5 is marginally stable. And I'm not sure where their scale drops off to unstable, but that's how their stability calculator is setup.

It use to be set up for 1.4 as minimal so that you had room to play with in case you were in a 'worst case' scenario, you'd still be above 1.0.

Since Litz has been on the higher SG = higher BC bandwagon, he's changed it to 1.5 as a minimum but I assure you, above 1.0 is stable.

Personally, I used to put way too much emphasis on this subject. I worry less about it now. I just know the limitations of my twists and shoot bullets accordingly. My opinion on 30 cals is that unless you're shooting above 215 hybrids or mono metals, the 11x to 11.25x is about as perfect a balance as you can get from 155-215s. Is the 11.25x the perfect twist for the 215? No but it works and it works darn well, even at sea level.

 

[hawk45]

At the end of the day, any caliber is only as good as the persons skill using it. If you dope correctly any caliber will be just as accurate as the next. Availability and reloading have lots to do with selection. If you don't reload, then you are at the mercy of factory loads. What if those factory loads don't shoot well in your rifle?? So if you don't reload, look for a caliber that many companies reload and in many weight and powder configurations. If you reload, all bets are off and just pick the one with the ballistics and reloading components you can find. Honestly, I've been thinking of getting into 7's for sometime, but can never find all the reloading components to put together the complete bullet/powder/case I wanted. Hell, even a complete set of dies are hard to find for some rounds. But I always can find components for .308 because it's so versatile and widely used, even though it's the #3 cartridge everyone hoards after .22 and .223. But if 20 rounds will do you for 3 seasons, any caliber will do.