At the very balmy Aug. 15 preem of Lionsgate’s “The Expendables 2″ at the Chinese, Simon West was sweating bullets.“This is the first time I’ve ever opened a film without a test screening, which is scary,” the helmer said at the Drais afterparty. “So I feel very relieved.” The 70-plus days of shooting — mostly in Bulgaria — concluded Christmas Eve. “I got out of there just before the snow arrived,” West recalled. Dolph Lundgren, whose Gunnar Jensen character includes a penchant for math genius, admitted that it’s the first time he’s acted a part in which his academic background came into play. “I got a chemical engineering degree and was studying at MIT, partly because that’s what my parents wanted,” he said. “Then I met Grace Jones and everything changed.” Lionsgate’s Jason Constantine noted that Sly Stallone came up with the idea of having Lundgren portray a brainy character. “It helps that Dolph really is a genius,” he added. Stallone offered heartfelt thanks to Lionsgate, West and his castmates when he intro’d the sequel while conceding that the premise seems far-fetched. “It made no sense on paper,” the star admitted.