Re: .340 Weatherby or .338 RUM
All things equal such as barrel length, throat length and chamber pressure with same bullets, the 338 RUM will offer slightly more performance then the 340 Wby will offer.
Also, it has cheaper brass which is generally much easier to get then 340 Wby hulls. The lack of a belt on the case is as mentioned a bonus as well.
About 100-125 fps of the 340 wbys velocity potential is due to its freebore chambers. When both are shot in rifles with conventional short throats, the 338 RUM will offer around 100 fps more velocity with same chamber pressures.
If you want to get into true 338 Lapua performance with out the .590" case head issues, Shawn Carlocks 338 Edge(338-300 RUM) is a great choice.
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