Captain Gregson's wife fires several rounds into the door, which clearly shows black, powdery marks. In the next scene, the black powdery marks are gone just leaving several clean holes.
Detective Bell says that a victim was shot with a Glock 21. Glock's barrel rifling is distinctive, so it's plausible that he knows it's a Glock, but he has no way of knowing whether it's model 21 (full size), 36 (compact) or 30 (subcompact), all of which use .45 cartridges.
At 13:20, Sherlock says that blood on the driver's side of the car comes from the left shoulder, but as driver's seat is on the left, it actually has to come from the right shoulder.
When they are searching the house, Holmes says that one of the two handguns in the bathroom is a Glock, but neither gun is actually a Glock.