I have this d boys ris set from velocity arms. the barrel that it comes with is very short (4 inches) unless you are using a longer barrel like the one that came with the gun it wont be able to house a longer inner barrel. If your battery is an 8.4v mini or smaller get the grip, if its anything bigger then it wont fit. For my gun, i ended up rewiring to the back.
EDIT:
http://torontoairsoft.com/product.php?id_product=329 this seems to be easier, although it says it wont fit a battery but it is cheaper.