I would guess you would add around 200 fps at the most. The round is only going to go so fast, really anything over 8" or so won't make it go any faster. I would step that round down to Corbon's 185 grain. It a rocken round!
I don't recall the source, but I seem to remember 1050fps from reading I've done on this very topic. All I know is that I really enjoy shooting my USC. It's an underrated carbine and makes a fine close in personal defense weapon. From across the room out to 50+ yards the thing is accurate and effective. For anything beyond that I really like the HK91. The proven .308 rocks at longer distances.
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