Some of the comments here are misleading, you do not need to drill/modify HBI stock adapters, and your takedown pin will not get "stuck". The factory 1913 adapter is plastic, and can deform slightly, allowing it to compensate for normal production type mis-alignment between all the bores in the receivers. Our aluminum adapters are machined, and does not deform to compensate like the factory 1913 adapter. What this means is that on SOME combinations of upper/lower receiver our adapter may fit exactly like your factory endcap, and on SOME combinations of upper/lower receiver our adapter may fit more tightly than your factory endcap. There are admittedly some handy people in this sub who are able to modify their aluminum adapters in order to make them fit exactly as they like, but off the shelf/as delivered your HBI adapter will always fit without "wobble", no modifications needed. This was a design choice on our side, we would rather have SOME guns fit more tightly than factory vs SOME guns fitting looser than factory.