There's been scant discussion about modifications on the new Slingfire, but I've heard that it accepts the omw 5kg spring http://www.orangemodworks.com/product_p/spg-u4.htm
Before modification my Slingfire worked very well and could be fire about as quickly as I could handle the lever with with darts getting respectable ranges a far bit further or around a modded maverick's.
After removing the air restrictor and replacing the spring I had a problem with a gear in the gear box slipping off. It turns out that the lever itself is not a single piece with gear teeth, but a gear held onto the lever itself with two small orange clips. I've since super-glued the lever and gear together, which now operates solidly although I have not tested it in a game.
I would appreciate any first-hand stories or information on modifying this blaster. If any of you know for sure if air restrictor removal negatively impacts range on this blaster I would be thankful because I did not properly range test the stock blaster and the ar-removed blaster with stock spring appeared to under perform.