Here is some general info that some may like to see:
"BBL Length vs. Velocity
This is from well known maker Charlie Sisk:
For a long time I have wondered about how barrel length affected velocity. I had always been told you need a certain length barrel for certain calibers. I have read when folks compared one gun to another with different lengths but I always thought that was not an apples to apples comparision. So I did a few test myself.
All these were Shilen barrels. I used the same brass through out the whole test. All weighed to with 1 grain. Bullets were tested on the Juenke machine. Powder charges were weighed to .1 grain. The same rest, chronograph, Redding press, primers all from the same lot, bullets for the same box, same lathe, same crowning tool, same cutoff tool, and each rifle done from start to finish on the same day. Ambient temperature was the same because I shoot from inside the shop. I held the rifle the same way on the rest every time. I shot ten rounds first to break in the barrel. Then cleaned with Sweets and fired one fouling shot. Then shot five rounds and took the average. I used a midrange load fron the Nosler book, not too hot but certainly not a reduced load. Here is what I got.
22-250 Hodgdon 380 34 grains Federal GM210M Remington brass 55 grain Ballistic Tip
27” 3469 fps
26” 3451
25” 3425
24” 3407
56 fps spread from highest to lowest
270 Winchester Hodgdon 4350 54 grains Federal GM210M Winchester brass 130 grain Sierra
27” 3115 fps
26” 3093
25” 3071
24” 3054
23” 3035
22” 3027
21” 3001
114 fps spread from highest to lowest
300 Winchester mag Federal GM215M Winchester brass 74 grains of Reloder 22 180 grain Partition
27” 3055 fps
26” 3031
25” 3024
24” 3003
23” 2984
22” 2960
95 fps spread from highest to lowest
340 Weatherby Federal GM215M 250 grain Sierra 81 grains Reloder 22 Wby brass
27” 2837 fps
26” 2817
25” 2809
24” 2791
23” 2777
22” 2755
21” 2731
106 fps spread from highest to lowestBBL Length vs. Velocity"
http://www.longrangehunting.com/forums/f19/barrel-length-300-win-mag-62018/index3.html