Retro Arms CNC Machined Aluminum Rotary Hop-Up Unit for M4 Series Airsoft AEGs

"I installed the retro arms hop up chamber in a Krytac CRB. It fit right in without any modifications. It was well machined and seems to adjust just fine. Has alot more precise tuning than the standard krytac hopup unit.

I've had the prowin, VFC, Krytac, Prometheus and the retro arms. Have to say my top two so far for adjustment and fit and finish are Retro Arms and Prometheus. Retro arms is all aluminum as opposed to the Prometheus having some plastic.

"Stupidly good hopup, like other reviews said you will have to trim your bucking but that does not affect performance in the slightest. The grooves inside the turn wheel make it a super solid turn that won't wiggle out of place during use. Also once you screw in the nut for the inner barrel it makes it tight with no wiggle at all. The only thing I had to do was shave my outer barrel a bit to make it fit inside the receiver, but that took two minutes with a file and it was perfect. Beware like other rotary hopups it stands high so it might be to tall for your receiver. All in all it reminds me a lot of the action army hopup for vsr10's in how it operates and once I get this thing out to areas bigger than my local cqb place I'm expecting easy 275ft+ shots on a r-hopped barrel/polarstar setup. 5/5