The realities of rising prices and increasing production costs have meant that some once-common size-classes of Transformers toys are now considered things of the past. One casualty of this phenomenon is the "Scout Class," once the go-to size to get a decent fully-featured character for under ten bucks. Coming out as part of the Cybertron line, Hardtop is a good example of this class.
I don't mean to suggest that Scouts were the smallest size of Transformers available back then. That's not the case at all, although even Mini-Cons were often sold in three-packs as part of the Scout Class at this point. But smaller toys such as the "Legends of Cybertron" tended to depict smaller versions of characters also sold at larger price-points. Scouts were "the real thing." Small in size, but typically with fully-articulated shoulders, elbows, hips, knees, and neck, and fully-participating in the main gimmick of the line (about which more in a moment).
Although fully-realistic alternate modes tended to be the exception more than the rule in the Cybertron line, Hardtop is readily recognizable as a dune buggy, if perhaps most dune buggies don't have weaponry like Hardtop's. But besides the fact that Hardtop is a Decepticon, Hardtop was characterized as a sniper, and thus would hardly be complete without this weapon.
Which brings us to Hardtop's utilization of the Cybertron line's gimmick of plugging "Cyber Planet Keys" into the figure to unlock special features. For Scout Class toys, the keys tended to plug into the figure's weapon, rather than into the figure itself, and with Hardtop, plugging the key into his weapon causes the barrel to flip over to reveal a longer barrel more suitable for sniping. Hardtop now stands ready to take on all opponents... from a safe distance.