Originally Posted by mcguyver
The FCC hopup uses a square spring, and a factory Systema as well as a modified hopup use hard silicone rubber cushions. The spring is going to be more linear, however is not as strong as the cushions. The cushions are vastly more affected by temperature snd stiffen up when cold, something the spring doesn't do. A strong spring is required to apply maximum pressure from the adjuster onto the BB.
A modified hopup uses a 3MM adjuster while the FCC is 2MM as well as the 2012 factory adjuster. It is fine, but the larger adjuster will form around the top of the BB once it is bedded in.
I personally prefer a modified hopup, but would like to replace the cushions with a stronger spring. FCC has the right idea, but the spring strength needs to increase by a large amount, something I am not sure can be done with the existing design of the adjuster cage. This is probably the reason why rubber cushions have been used for so many years and through all design changes.
There are pros and cons to both.
on all their 2013 FTW, complete rifles and hop up kits will have the stronger spring, I too prefer the modified Hop but in winter its a pain as Brad say it will stiff/freeze on you. I have used both in extreme winter conditions (-25 -30C) and the FCC hop have no issue