It could be a mental thing. Ive seen it several times, someone is trying to shoot farther than they ever had and cant group at all. Just remember the basics. Shooting at 40 is no differant than shooting at 20 or 30. You need to make sure your doing everything exactly the same except use your 40 yard pin. It maybe farther than you have ever shot before just keep in mind its only 10 yards. The farther you shoot the more exagerated your flaws in shooting form will be.