Reading the stock hop up wasnt very good for the VFC SR-15 E3 IWS was ordering, I ordered one of these too. It came in shortly after my gun did and I immediately went to install it. First thing I noticed was the middle gear is completely teethed, there is no stopper. I wasnt thrilled, but I went on and tried it out. I shot and I had no hop. Turned it all the way on, and still no hop. Examining it, the nub was too soft to bush down on the bucking (ironic because it was a Systema bucking). I put in my stock nub and it shot fine. This is someone irrelevant though, because you should be getting an SCS anyways (mine was out of stock at the time).
Then I noticed my bolt catch wasnt functioning properly. The bolt plate was rubbing on the gears for the hop up, hard enough it would actually change the setting on my hop up. I tried trimming the adjustment gear, but it still rubbed. I modified my stock gears to fit the Systema chamber, and it barely clears the adjustment gear, but hits the middle gear (which as thin as it already is, I dont want to shave). Obviously, for those who dont have a function bolt catch, this is irrelevant, but could be a problem for those who do. It actually got bad enough it got stuck, and I over-stretched the bolt plate and charging handle springs trying to get it out (luckily VFC sent me new ones for free).
Runs a little wide
No stopper on the middle gear
Nub was too soft
Rating: [3 of 5 Stars!]