Sgt. George “Loaded” Lockhart, one of the Marine Corps’ top martial arts instructors, has said he plans to open a gym this summer with rising UFC star Brian Stann. Lockhart, who is set to leave the Marine Corps in July, said he and Stann, a former Marine captain and Silver Star recipient, hope to co-manage the gym in Alpharetta, Ga., near Atlanta. The two of them are both quickly earning names for themselves in the UFC — Stann as the underdog fighter who crushed Chris Leben in a New Year’s Day victory and Lockhart as a diet guru who helps…