Need some help
 

I currently own a CA m15
it;s been upgraded with systema gearbox, tightbore etc...
but i want to change the front end to be somthing like a s-system.

now my gf is going to come with me to the game
i need a cheap gun for her

so what i think is i would buy
a JG- M4s system or a Dboys M4s system

the JG is ABS+metall rail
the DBOYS is full metal

i am going to take the SIR and install it to my M4
and build an cheap one with my spare parts
however i dunno if the SIR from those 2 model fit on CA m15.


what do you guys think? and which one i should take?