I've never used GMX's.
I've only shot 1 big game animal with a 22 cal, an antelope about 5 years ago. Antelope tags in Idaho are VERY hard to draw. I'd been reading about guys hunting with 223's. I don't own one but I do have a 22-250 so I thought I'd give it a try. I had some 55gr Sierra softpoints on hand. It's a slow twist barrel and larger ones aren't as accurate.
My shot was only about 75 yds at the most. We found them bedded in a grassy bowl in the lava beds. We sneaked in and just peeked over the top of the rocks right down on them. I got a heart shot. The bullet tore the heart in half, hashed the lungs, and I found it in the far shoulder. He ran about 20 yds.
