There have been several attempts over the years to build a .22 WMR in semi-auto. I've not kept current on them, but in the past all tried, and none proved 100% reliable.I picked up an Alexander Arms 17hmr AR upper several years ago, and I liked it so much I bought a second one. I stocked up on ammo when it was still cheap and probably have enough that my kids and grandkids will be shooting it well after I’m gone. I’ve killed a bunch of stuff with my 17’s from crows to wild pigs, but like like Dennis, I’d prefer a 22 magnum with heavier bullets. However at this point, I’m too heavily vested in the 17’s, and though I’m not necessarily an AR guy, I like the 17 on that platform and don’t think there’s a quality AR alternative in 22 magnum.
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There are some new manufacturers out there that are theoretically coming out with .22 WMR simi auto's but have yet to be put through the torture test of reliability.