This has got to be the best thing that has ever happened to the MAC series of weapons. Brand new side cocking with an FN-FAL style charging knob that does not cycle with the bolt. Man - you can get the classic hollywood movie style grip on your MAC. Makes rapid bump firing easy and safe since you can get your hand wrapped up behind the cock knob and around the receiver. The other major benefit is you can now get it with a scope mount since theres no cock knob on top. Master Piece Arms is making the MACS now - brand new - post ban in pistol and carbine configurations. Affordable as hell - you can buy their M11/9 (MPA30) $275, and M10 45acp (MPA10) $375. Their making these side cocking upper receivers to retro on to all the MACS including subguns, in post and pre-ban configuration -thread or no thread. You have to get this stuff from their distributors namely www.RPBUSA.COM and or Jeffs Shooters Supply. The upper receiver is a drop in conversion with your bolt - a 5 minute deal. Costs about $135. Available with or without scope rail. This is a great cheap way to put a new face on your MAC!!! Makes shooting your MAC a dream!!!