Just got an MTM K-Zone shooting rest delivered today. Just wondering if anyone else has one of these and if you've bothered to load it up with something to help keep it planted or have just used it as-is? I'll primarily use it for zeroing and wondering if it's good to go out of the box for AR and AK calibers or if it's really gonna need some filler to keep it in place for .223 or 7.62. Seems like a pretty flexible and handy shooting rest to have so far though.