Muzzel velocities

[Dave King]

Welcome to LRH!

I don't have a 338/416 (yet) but I've had 338 Lapua and 338 RUM and one can figure to get 2775 to 2900 fps out of these with a 27.5 to 30 inch barrel and the Sierra 300.

These two cases are about the same in case volume and are essentially shortened 338/416s.

As for using a 505 Gibbs, I recently had a fella tell me Prairie GunWorks had something in 416 on a 505 Gibbs case and the 408 Cheyenne is using a case derived originally from 505 Gibbs dimensions. I don't know how well a 338/505 Gibbs would work, probably way overbore and beyond efficient use.

[Coyoter]

First off, I'd like to say "Hi" to everyone on the board. I've been sitting back and reading for some time now without registering and you folks have definately piqued my interest.... Several $k worth if I know me!
I've been reading up mostly on the .338/416 IMP, but am open to other suggestions. The posts by Darryl incicate a muzzel velocity of 3100 fps with a 300gr Sierra MK and a 37" tube. I'm curious what that would work out to with a 26" tube, or how much velocity per inch is gained/lost. It's not that I want to build one of these on a 26" tube, but folks like Lazzaroni and Weatherby don't list velocities for their factory ammo with 37" tubes, so comparison is tedious to say the least.
I've had it suggested that I build on a 500 Jeffery or 505 Gibbs. That would be fine, but how long of tube would those cases require to generate 3100 fps? How much of a factor would throat erosion become if I reached the same velocities in a shorter tube?
Thanks for your time and input, Ty S.

[Fergus Bailey]

Darryl could probably give you some actual data on velocity from a shorter barrelled 338/416, but as an estimate I would guess a velocity reduction of 20 fps to 25 fps would apply for each inch of barrel that is removed. This would mean a barrel of 26” to 27” would get velocities in the order of 2850 fps to 2900 fps.

I do stress that this is a guesstimate, not based on actual testing with this round.

Fergus