I've shot a few HK's including the PSG-1 and truthfully I wasen't to impressed especaily for $10,000+ gun. Thier were a couple AR's their that wouyld shoot with it and they all would shoot with a few of the Bolt guns but the custom built bolt rifles that their chamber was cut for the ammo they were shooting were way more accurate
My .02 cents is if you are not going to utilize the capabilites of a semi-auto reciever,then why have the moving parts in a LR just for "decoration". Maybe I am missing something like "a rapid fire course" at the 1K line, though it might be fun.
Hi Armalite makes the 300 REm SAUM but i believe it would be much better in 7mm REm SAUM because of the ballistics potential at long ranges with a Sierra 175gr MAtchKing over the Rem Factory 300 Rem SAUM loads with the 190gr MatchKings.
Their are other manufacturers that are making semi's in larger cals and i believe their is at least one manufacturer that makes an AR type in 338 Lapua.
The Biggest downside is that the Semis to be as accurate as a bolt action are almost twice the cost for the same accuracy.
That is possibly why the bolt guns are mainly used but if you want one by all means have a custom rifle built in an Ultra MAg in 7mm or 300 with match Quality gear and the custom manufacturers that make them and you would have an awsome long range rifle capable of quick follow up shots but the thing is that you have plenty of time to reload a bolt gun while the projectile is still on the way to the target so their is not that much advantage over a bolt gun anyway but you have the right to use whatever you like in the US anyway.