Hey guys, I may be behind the times here but picked up a brand new gsr 35 gen 2 for my 16" colt upper.  

I installed it and my question is it says when the bcg is locked forward you should be able to move the piston cap so there is a gap the width of a dime if I read it correctly?

Well on mine I got about the thickness of a couple pieces of paper.  Not much play but it's not forced against the op rod.  Well this be ok?  And btw I have it mounted with a magpul moe hand guard and there is ample room for it.

I had one several years ago. IIRC, the instructions said the thickness of a business card. I don't recall a dime!?! Regardless, I suspect you're fine based on the gaps of several other piston driven firearms.

Thanks for the info.  It seems more reasonable to not have a lot of play as long as it's not slamming back into it when it returns to battery.  Also the instructions that were sent were for the gxr but I have the gsr.  
Thanks again

Just as long as the op rod / piston socket has some movement when the carrier is firmly against the barrel extension when the bolt is locked then you should be OK.