Marginal stable bullets?

[coop2564]

how many are getting very good groups with marginal stablized bullets?
My 270 has 10 twist but i want to shoot 150gr LRAB twist calculators say it will be marginal stable 1.34! Show bc would change from.591 to .554 which is still better than most other bullets that would be stable 1.5 or better!

 

[elkaholic]

The problem with marginal is at long range. You can sometimes shoot extremely good 100 yard groups but lose out at long range.

 

[coop2564]

Is there a rule of thumb how far that would be ? 500, 800?

 

[elkaholic]

Is there a rule of thumb how far that would be ? 500, 800?

Depends on how unstable but not too likely at 500 yards.

 

[coop2564]

So no one is using this bullet in a 10 twist?

 

[Mikecr]

1.34sg is not 'bad', and goes up further & further downrange. Optimum for bullet or not, stable is still stable.
Also keep in mind that local stability changes with air density.
So run & consider the numbers under conditions you intend to shoot at.

I run 139 Lapuas at 1.3sg here at seal level, while shooting is intended at ~1500ft elevation, where gyroscopic stability climbs to ~1.5. Thing is -it shoots just fine here.

 

[BallisticsGuy]

I routinely run Sg's down to the low 1.3's. Sg increases as the bullet loses velocity down range. Velocity decays a TON faster that gyroscopic spin. The forces trying to flip the bullet over at mach 3 are a lot higher than at mach 1.5 after all. You will quite probably lose a little BC, something like 3-5% probably. Under 600yrds it simply won't matter enough to say grace over.

 

[cohunt]

I run the 150 lrab in my 270 win with 1:10 twist but I'm at 6500msl

 

[coop2564]

Thanks Guys Ill give them a try!