the L3i BMR magazine block will easily lock into the magwell and prevent your bolt from closing. This is a great way to visually show your action is open on the firing line. As with all magazine blocks it will not indicate if a live round is in your chamber and you should always verify the chamber is empty prior to installing the mag block for safety.
Fits perfectly and is a nice little accessory made specifically to fit the BMR mag well. None of the other empty chamber flags I own fit into the .22 LR chamber for true safety at the range or anywhere you want to flag an empty chamber. This block is visible below and above and fits the bill.