Our team has ben using two of these barrels (Version 2's) in ICS M4s for the last month or so. I used to have a Systema 6.04 in my ICS (borrowed from my TM M4), carried out light upgrades to the ICS, and shot some before and after groupings. The Madbull barrel produced ever so slightly tighter groupings then the Systema, and I had less flyaways. I'm quite impressed with them, and they're affordable to boot!
South Island Rangers Airsoft - Victoria, BC