When it comes to rifles the general focus in the training industry is on manipulation of the weapon while vertical. That is to say that the focus is on how to run the gun while one is upright. However, when you consider what a rifle is for (the long shot) it makes more sense to know how to work with it from the ground. I have attended way more ground fighting training than any one man should when it comes to the discipline of rifle. Rolling in the dirt with a rifle is something that I'm well acquainted with, and you should be too. Here, in this video is just a small snippet of information for you along those lines.
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