See my new post (today) on building a single shot 338 RUM. The short match action is far stiffer than any "open top" and will eject empties w/no problems. The left port load is plenty fast enough as this is not a "running jackrabbit rifle".

338 RUM is the choice, why ? FACTORY AMMO if you need it, which BTW is very accurate as well.

I figger with the 300 gr Berger and a 34" 3 groove nitrided tube, getting very close to 3000 should be do-able.