I've never had a .338 Federal but have had a .338 Win Mag and .338-06 with 22" barrels. My .338-06 got around 2700 with 225s. A couple inches less barrel would probably take 50 fps or so out of that number.
You didn't ask this, but if you're concerned about velocity, one other thought is a .338 Winchester Magnum. It's a pretty moderate cartridge and loads down well with medium burn rate powders to .338-06 or .338 Federal velocities. I've never had one with a 20" barrel, but my 22" guns have been fine. I wouldn't hesitate to do a 20" gun, especially if loading 4895, 4064, RL15 or some other powder in that range.
