98 C low velocity problem

Hi, I'm new to the forum. I have 2 98 Customs and I just finished polishing the internals. Both guns are set up with RT, Expansion Chambers, running CO2, one using a flatline and the other is a 14" barrell. Triggers and drive springs are stock. They have both been used about the same for about 3 years. One is actually my sons, I do all the maintenance, cleaning, and upgrading myself. After polishing the internals as suggested on the forum I decided to have the velocity chronoed. The guns were shooting around 250 fps with spiking of 220+/- to 260+/-. The pro shop dude said he could not get the velocities up past 250 or so with the velocity screw almost all the way out. I read some the other posts about this topic and I am considering new drive springs but I was wondering if by polishing the internals I may have caused this problem. It seems to me that I should be shooting to high after the polishings. Any help is appreciated. Sorry I'm such a rambling windbag!   :)

Thanks all - I've got 2 new stock springs on their way from Tippmann. They didn't even charge me!

I used very fine steel wool by hand just to take off the paint overspray then used a soft clothlike wheel on a dremel tool with a little pollish to get a shine. I don't really think I could've taken off too much material. Anyway, thanks again.

I'll post my findings when I get the new springs.