The KJW has a very wide bore barrel as stock (6.10 or something daft) so it needs a replacement; I believe the Tanaka has a tightbore as stock (not 100% sure though) and the Tanaka uses a proprietary hop unit, rubber and barrel whereas the KJW uses a VSR rubber. The KJW M700 can take AEG barrels but they need a groove cut into them just in front of the hop window for the VSR rubber to fit onto it.
KJW mags also tend to be terrible and Tanaka mags are much better. They're all compatible with each other but you'd be paying £50 or over for a long Tanaka mag (the long mags give the best performance as they can hold a higher volume of gas and more than 10 BBs)
Yeah, there's one which allows VSR barrels to fit the Tanaka (http://www.evike.com/products/28726/) but I don't think there are any VSR barrels long enough for the rifle. You're best bet would be to buy a PSG-1 barrel and cut a groove into it for the 'lips' of the hop rubber to fit into. I can supply you with measurements from my stock KJW M700's barrel. The best way to do this is on a centre lathe, however I'd heard of people putting the barrel into 2 rotating bea...
Wow a lot of work huh? You own a KJW M700 then I assume? Would it be pointless to by that conversion you linked for the KJW? First time with a gas sniper you see. For the three years that I used a sniper rifle they were all spring.
That conversion kit's for the Tanaka to use a standard VSR barrel and hop rubber, the KJW can use them anyway. And yes, I own one- I'm currently going through the process of making mine useable as a squad level marksman rifle, it's only really possible to use them as dedicated sniper rifles with an HPA or Nitrogen rig propelling the BB
involves a fair amount of machining. Unrustle Thine Jimmies knows what parts to buy for an HPA conversion, as does PT247 (he's got his KJW M700 up for sale with an HPA converted magazine included, all you'll have to buy is a compressor and a line for it