It's probably mostly from the stock, these Magpul PRS stocks weigh a good 1.5lbs more than a typical stock. Surprisingly, it's not difficult to shoulder my rifle at all, but I can definitely imagine feeling fatigued after firing 10 rounds. I also can't imagine I'd ever want to take this thing hunting
Someday I'll build a lightweight .308 for that purpose, but I gotta let my wallet recover first.

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