You would benefit the most with the heavy bullets, like a 208 A-max, 210 VLD. Depending on your range, you could load up some 155's for flat shooting. I'd look at Retumbo and a 208 as my first choice, though.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: jvm</div><div class="ubbcode-body">I was hoping someone had chronagraphed a long barrel 300 win,
what the reloading books say and what is real some times don't match up </div></div>
Plan for about 15 fps gain per inch of added barrel length, give or take a few fps. Plus, it all depends on what load the rifle likes to the velocity you get. I can get 2850 fps easily with a 208 A-max in a 27 1/8" barrel. You can push it faster with a slower powder up to about 2950 fps, plus your added barrel length. A 190 grainer can go 2950 to 3025, maybe a hair faster. A 155 should run about 3200-3300 fps at max charges, then add your barrel length. A 110 grain V-max can run 3750 to 3800. This should help.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Pat M</div><div class="ubbcode-body">In my opinion, shooting the lighter bullets 155-175 is a waste, you don't get a great increase in velocity so you might as well get the punch from a heavier bullets 190-220 </div></div>
You don't need much punch for prairie dogs. For 300-500 yards, the 155's would be smokin' for a p-dog town with little drop. A 110 V-max would be total carnage.
155's from a 30" barrel should be very fast. You may end up not reaching the target because they self destruct. I shoot them at 3100 for accuracy from my 30-06 and 26" and I've gotten over 3200 when I really lean on em. Start with the advice here and work up from there, that's the best approach IMO.
I have a 300WM hunting rifle, and I won't shoot it a lot, maybe 50-75 times a year, if that. So, if you get 1500 rounds out of it, that will last a long time. Why not have a hot rod 300WM. Velocity does kill!