Hail Hydra. MGI Multi-caliber AR Posted April 24, 2014 in Other Gear & Gadgets by Nicholas C with 28 Comments MGI made an AR that is multi-caliber. So what, many other companies have a multi-caliber AR. Well this can switch from 9mm – 7.62x39mm – 556 within minutes and without any tools. Check out MGI for more info.