I actually know nothing about the UK Arms but if it is infact a clone of the M28 then I think I can help,lol.. The pistons will be ready soon I hope. They are able to take a beating.The hopup is like a mini version of the Vsr. The hopup arm fits. I suggest cutting of them terrible fang type nubs on the arm and gluing on a rubber bucking. Them fangs eventually chew into your bucking and you end up having to replace it every so often. I used soft rubber wire casing instead. I shimmed my hopup arm and did the Tdc hopup mod. The barrel spacers the m28 comes with are already good..
I suggest doing the teflon tape mods, cylinder head threads and bucking. As for the lower fps. I would get the laylax pss10 120sp. That gets you about 400fps roughly. Then since you did the teflon tape mods. Reports I read say that wrapping the cylinder head threads gives up to 50 more fps. Lets just average that to 25fps.. right there gets you 425-450 ish.. I would honestly say keep the stock inner barrel because its actually pretty nice. Many people are arguing tightbore is only for short to medium range, not long range.. Personally, I dont care for tightbores either.
Accuracy has to do with the ammo also of course.
I dont know how much knowledge you have on these things so I just over explain just incase..
Am I missing anything guys?
Oh, a good steel piston sear is a nice thing to have when dealing with metal pistons. Ours is aluminum with a stainless steel sear catch. Currently my buddy is having some issues, so I'm not certain how long the hold up is, but I'm certain its worth the wait..