300WM,190gr projectiles,2990fps out of a 24" barrel.From the same barrel mfg,what kind of velocity increase could I expect from a 30"?

maybe 150 feet/sec

That's about what I thought too.

For what it's worth Loadtech calls it more like 110-125.

quickload says 180...


and ..split the difference, and you get 150fps ...

LOL

Nothing a game animal would feel a difference from, or that would make you notice a difference in trajectory. Nevertheless, one of these days I'll finally shoot out the snubby 24" barrel on my .300 Weatherby Magnum Vanguard and put on a 30", because that seems to be about the longest "standard" replacement barrel.

In recent years I've been more interested in old milsurps than anything, and I just love the old standard long infantry rifles. Can't imagine why anyone ever wanted to "sporterize" a Gewehr 98, which I think is an ideal rifle just the way it went into the hands of the Kaiser's troops, but that's another topic. I don't find them unhandy, in any case.