FWB150 velocity

I picked up a 150 a few years ago at a gun show, paid 300 for it. Good blue, good original stock finish without the typical crack at the wrist, never been rebuilt. It shoots great, H&N wadcutters and RWS R10's both shoot around 540fps. Is that right for a 150? Was thinking of sending it off for an overhaul so it would be good until I die, just hate letting it go off into the unknown for a month or two for the refurb. Thanks--
 
Thanks Joe, I thought it may be a bit low, I was pretty sure the fwb150's should shoot somewhere is the 600's, but wasn't sure. I guess I will get it packed up for a rebuild so I have it to shoot in my basement this winter. It does shoot very consistant and accuracy is right where it should be. Off the bench at any reasonable distance you cannot tell how many shots went into that little hole!
 
My 150 is @680fps with Meister pistol, I found a rare forearm stock weight for it too

1537733391_21200806075ba7f30f711810.60589177_110 FWB 150 stock weight.JPG