The A.R.M.S. Number 71L sight set is a durable polymer back up sighting option. The #71L-R and #71L-F use the same metal posts and apertures as their standard iron sights to provide heat resistant performance for both CQB and long range shooting applications. These spring loaded sights deploy with the push of a button and are held in place by spring tension, allowing them to collapse and avoid damage when dropped. Not designed for use on railed gas blocks.