Needed to attach brass catcher to 2nd upper - Caldwell AR Pic Rail Brass Catcher, Spare Mount

The Caldwell brass catcher is a required item at the range so that you don't have to chase brass all over the place when practicing with your AR-15. I bought this brass catcher for the original upper and wanted to be able to use it on the heavy-barreled upper, also. When the catcher is detached, the rail attachment doesn't detract from the lines of the upper.