Funny, I was just on the phone with the gun shop and this very subject came up. The guy at the shop said they were planning on building several ARs in 9mm, .40, and 45ACP. They said they were going with the Olympic Arms uppers instead of the Dalphon uppers. He said the Oly uppers have a little bit better quality.
As for me, I'm waiting for the Victor Arms dedicated 22LR upper.
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"Ray guns don't vaporize Zorbonians, Zorbonians vaporize Zorbonians" The Far Side