I think too much is made out of the "seat the projectile out". Real world advantage is small and generally lost in the nose, unless the extra space allows you to drop a burn rate or two and still fit enough in for max velocity. This isn't the case with the 280ai as there is plenty of room for suitable powders, 2217, N560, RL22 etc.For my 280ai I load 162 amax at 3.380 OAL with 61gr N165 for a lazy 2925 in a 23" barrel. This has the boat tail/bearing surface interface inline with the neck shoulder junction. The 280ai has a long neck.
You can load longer in a LA 700. 3.6" ish ? IIRC. which should have the base of 162 amax at the neck/shoulder junction.
The 280ai and 7mm saum are balistic twins and behave as such, similar barrel life , similar speeds in any given barrel length. Both will out run the 284.
Any of them will be fine so build whatever you have a hankering to build.
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