we scar fps issue

[Mtemprell]

I have just upgraded my we scar to fire around 330 fps from the out the box 260 I have installed a madbull 6.03 tight bore barrel a g&g hop up rubber and a madbull 110 spring. Iterated my riffle after this and it was fireing at 340fps. So I took it to my skirmish site at weekend and was obviously expecting a fps drop through the day as it beaded in. Tested it halfway through the bay and my for had dropped down to 290. What could be wrong? Is it a better air seal need? Since then I have wrapped the hop up rubber and chamber with ptfe tape but haven't tested this as of yet.

Any thing else I can attempt to get my fps back up?