Regarding the 6.8 I would stay with the SPC reference availability of ammunition in most major sporting goods and larger gun shops. The two calibers I am partial to are the 458 SOCOM for accuracy as well a "stomping" game. (Pigs DRT!) And the 6.5Grendel for accuracy and longer range shooting. Have also killed deer, pigs, coyotes and prairie dogs at long range with the 6.5. Both of mine are sub MOA guns.
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-- John F. Kennedy