Re: Ballistic Changes with 18" barrel
DTA SRS Covert with an 18" Bartlein 10-twist barrel:
FGMM 168 gr = 2591 fps (mean of of 2 x 10-shot string average MVs; String 1 = 2582 fps, String 2 = 2600 fps)
As Pusher stated, the 168s in your setup are not going to be ideal past ~800 yd. At 2591 fps, they will be going trans-/sub-sonic before 900 yd, which the 168 gr SMK doesn't handle too well. The 2591 fps MV was from a bolt gun, so you're probably looking at slightly less than 2591 fps. The Hornady 168 gr A-Max will do a little better, but still not where you would like to be at 1000 yd. I've used 155 gr Scenars (CorBon factory load) from this setup at better than 2800 fps, and they shoot very well from the 18" 10-twist barrel. If you can push 155 gr Scenars close to 2800 fps, you'll be doing better out to 1000 yd than wih either of the 168s mentioned above.