Revised edition (August 2025) of the Retro Arms CNC aluminium hop chamber.  This is what they now call the BASIC version, I tend to use either this chamber or the plastic ZCI on all the majority of the builds I work on.

For this new version they have slightly modified the feed and bucking shaft size to allow better compatibility and improved feeding.  Gone is the black annodised finish in favour of grey.  The anti-rotation collet nut also seems to work a little better but never truly stops the barrel for rotating.   Like the previous version this comes with a standard arm for omega shaped nubs and a TDC arm that works really well. There's an o-ring on the feed tube to prevent BB's from dropping when changing mags.

Apply a little silicone grease to the hop wheel and oring. The chamber comes non-assembled so you'll need to put it together.