Ruger MKII carbine project

[Akaishinobi]

I'm trying to upgrade the KJW MKII Carbine ( http://www.airsoftgi.com/product_info.p ... cts_id=774 )
What I want to do is downgrade the FPS to between 359 and 380 , find/make a rail to attatch to the barrel so I can equip a grip, and fand/make a set of points to attatch a sling.
The issue here is that I don't know where to start. I assume that, there there is a way to lower the FPS of a Gas non-blowback Ruger, it'd be to get a new valve, but the only ones I can find are the high power valves that were in the old models. Does anyone know of low power valves I can get, or any mods that would allow me to lower the FPS? And also if you know of any rail/ sling attatchment for the Ruger carbine or any ideas for making them, I'd be happy to know. Thanks in advance.

[2nd Ranger]

duster gas, aka HFC134a will lower the power, how much I do not know, probably about 100fps lower though

[Akaishinobi]

duster gas, aka HFC134a will lower the power, how much I do not know, probably about 100fps lower though

Thanks, that is one way possibly, but just in case it drops too low by chance, I'm still wondering if there is a valve somewhere out there that will do the job with green gas

[Dominum]

Cut down the hammer spring or even the hammer itself (The latter is permanent unless you have a spare). BTW, it is a MKI, they have it listed wrong. Do not expect a whole lot of accuracy out of it unless you custom make a hopup for it. Also, rather than a sling, you can simply slide the barrel into any molle on your back and it will stay there just fine. Due to it's ridiculously low weight and lack of front heaviness, a forward grip is totally pointless and would be a waist of time and money (not to mention it would look funky).

[Akaishinobi]

Cut down the hammer spring or even the hammer itself (The latter is permanent unless you have a spare). BTW, it is a MKI, they have it listed wrong. Do not expect a whole lot of accuracy out of it unless you custom make a hopup for it. Also, rather than a sling, you can simply slide the barrel into any molle on your back and it will stay there just fine. Due to it's ridiculously low weight and lack of front heaviness, a forward grip is totally pointless and would be a waist of time and money (not to mention it would look funky).

How much would it cost to get a custom made hopup averagely? And I could use that trick with the molle as long as it fits. And I knew it was listed wrong. Thanks though. I was planning to try out replacement springs. I was refered to a site that went into detail on increasing/decreasing the FPS on the Mark I Ruger, and it gae me the spring measurements.