Standard loading practice for 155 grain bullets in a 30" barrel .308 gives 3000-ish fps. (some people shoot at 2950fps and win matches, some shoot at 3050fps and win matches, some even try to get 3100fps or even 3150fps in an attempt to get an advantage but I honestly don't think there is advantage to be had there...).
A reasonably decent way to estimate what sort of speed you might be able to expect with a different weight bullet but loaded to similar pressure and using a powder selected to be suitable, is to figure out the m.v. that gives the same muzzle energy.
To cut to the chase, this is the speed you can expect with 200 or 210 grain bullets:
Sqrt[155/200]*3000 = 2641fps for 200 grain bullets
Sqrt[155/210]*3000 = 2577fps for 210 grain bullets
Sqrt[155/230]*3000 = 2462fps for 230 grain bullets.
It would be surprising to see your max velocity end up being much different than these figures. For what it's worth kombayotch's report indicates speeds of 2589, 2594, 2611 and 2635 for four different 21-class bullets, Reloder-17 and a 26" barrel (i.e. a bit better than one might expect from my results above, but still very much in the neighbourhood)
Another thing to consider is whether the bullets will stabilize in your rifle. For a variety of reasons bullet manufacturers use deliberately-conservative figures in the "min twist needed" figures that they publish. While your 12"-twist rifle doesn't meet Berger's recommended "11 or faster" figure, there's a good chance that it will work. You can use one of JBM's calculators to calculate the Miller Stability figure - I used
http://www.jbmballistics.com/cgi-bin/jbmtraj_drift-5.1.cgi
To calculate the stability factor with the Miller method you'll need to know not only the usual bullet bc and muzzle velocity, but also:
- barrel twist rate
- bullet length
- bullet weight
- air density figures (pressure, altitude, temperature)
Fortunately Berger publishes a nice table
http://www.bergerbullets.com/Quick Reference Sheets 10-28-11.pdf of the BCs and also the physical dimensions for Berger bullets.
I did a calc for the
Berger 210VLD and got a stability factor of 1.24 using mv=2577fps, G7bc=0.323, twist=12", bullet length=1.459", weight=210, temp=59F, humid=0%, press=29.92"Hg.
A stability factor greater than 1.0 indicates that the bullet ought to be stable (there are a bunch of is and gotchas, which is why the standard wisdom is "you need Sg>1.4"). So while there are no guarantees that a Berger-210-VLD will be stable out of your rifle, I'd be inclined to bet pretty strongly that it would be stable.
For what it's worth a Berger-230-Hybrid @ 2466fps has a Miller Stability factor of 0.954 under the same conditions, so it will almost certainly *not* stabilize from your 1-12" barrel. Out of an 11" twist barrel though there is a fighting chance (Sg=1.136)
