Won’t hurt anything but your neck. That’s why I recommend the 40 round Pmags. Much more comfortable.
We shoot like that on one of our drills, 5 standing, 5 kneeling and 5 prone on a USPSA silhouette at 200 yards, shot for score and time.
Won’t hurt a thing.
My old prone slow fire position was low enough I could have used a 20 for a rest... it was illegal so I had to get higher. Neck was never an issue but I'm 15 years older by now.. lol
