Just bought a Sig 220 stainless at a gun show, it's shooting about 6" low at 15 yards. This is not from a sandbag but from a braced position. The gun was previously owned but appears to never have been shot, although it has Hogue grips instead of Sig. Should I spring for adjustable rear sights or taller rear fixed sights; I've never had this problem with fixed sight autos before. I'll let someone else shoot the gun before I do anything.