I had a 458 Tromix upper (second one Tony ever built if I remember correctly) but sold it as I never really had time to shoot it (was stuck in my 50 bmg stage at the time).  But now am interested in getting a like upper again.  

Now the hard part..with all the new calibers, (458, 499, 510 etc) what is the hottest round available for the AR right now.  Keeping in mind, I still want to be able to shoot in semi and still use AR mags.  

[url]http://www.ar15.com/forums/topic.html?b=3&f=118&t=158865[/url]
[url]http://www.ar15.com/forums/topic.html?b=3&f=118&t=138911[/url]