Southpaw service rifle shooter here:
In the prone position, I'll dismount the rifle and position it so the butt is near my ribcage and the muzzle elevated. That makes the ejection port accessible to where I can grab a round and easily insert it. I'll elevate the butt to let the round slip into the chamber, shoulder the gun, then release the bolt with my left trigger finger. Taking the gun out of the shoulder to load is a pain as it forces me to rebuild my position each time.
I have seen lefties that can keep the gun in their shoulder and reach OVER the gun to load, but that seems like too much trouble for me.
Quote History Quoted:...Grab one, drop it in the ejection port, hit bad lever.
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If you're shooting sanctioned CMP matches then the MAGPUL BAD lever is not permitted on service rifles.