Personally, I think the Recon class could use some extra anti-materiel capability to harass vehicles like tanks and BTRs, ideal for supporting engineers or maybe finish off a vehicle nearly exploding.
For balancing, I think AM rifles would be an obvious one shot to a human, and then chip damage on tanks, around 15 on a LAV, then 18-20 in a transport...
First suggested option: Barrett XM109 (25x59 mm) - could be balanced to fire slow and limited to 5 rounds (7 round extended).
Second suggested: McMillan Tac 50 (50 BMG) - bolt action, 5 round 50 Cal rifle