I have two 338 Lapuas now and have built several for others. Also a bunch of 338 ultramags and 338-300 ultramags or some call edge on here. All of them are the same with the individual barrels being the difference. You will top out between 2800 and 2900 fps with all three with 30" barrels.
+1 on what Broz says - my 338 imp Lapua w/ 300SMK and 98 gr Retumbo gets 2925 on Chrony, but 2850 works with exbal on 29in barrel. Haven't tried for more, wanted to stay under pressure as it is built on a700 action.
I shoot a .338 ultra mag, and when doing load developments I was getting an average of 2865fps over three shots with the 300 smk. the load shoots nice groups but I'm wondering if that seems a little on the fast side. I single load so my OAL is 3.830" with 94 grains of Retumbo. temp was 6 degrees Celcius (I have no idea what that is in F) . elevation 2900'. Could it be that I have a fast barrel or is my chrony most likely inaccurate? I was also getting 3390 fps with 210 TTSX's.
Sorry for kinda off point, but it seemed close enough
Of the several dozen Lapuas I have built I would say on average you will see 2800-2850 fps with a 30" barrel length. The Lapua case will handle an extreme amount of pressure and some barrels are simply faster then others which is why you see the occasional +2900 fps velocity reports but on average, you can expect 2800-2850 fps with pressures in the 65,000 to 68,000 psi range.
300wsmmad, I can not imagine any 338-300 ultramag, or edge as you call it, getting 3300 fps with a 250 grain bullet. That chrono needs to be checked. There are few people around who have the experience with that cartridge as I do and I have chronographed over a hundred of them. None of them would ever even aproach that kind of velocity safely. 3300 fps with a 250 grain bullet is getting into 338-378 weatherby velocities and the 378 case is way more rifle than anything off the ultramag case.
Again, to answer the question, the 338 Lapua will top out between 2800 and 2900 fps with a 300 grain bullet in a 30" barrel. Which is the same as the 338-300 ultramag, or edge, and 338 ultramag. Some rifles shoot much better in the 2700's and get erratic in the 2800's. Just depends on the rifle. For comparison the 338-378 Weatherby seems to like 2975-3025 fps for best accuracy. Like I said"top out", not necessarily where it will shoot the best.