late 90s Raleigh Special Products 853 seatpost diameter?

Hi
I have a late 90s (I think) straight forked Raleigh 853 Team frame. Recently was about to use a 27.2mm seatpost I was given but would only go in 8cm quite tightly by gentle opening by a millimetre of the seatpost clamp area. Im not going to force it. Does anyone know what seatpost diameter Raleigh used on these frames/tubing of this era? The curent seatpost is stamped 27.0 and I measured the current seatpost with a Vernier calliper and it is 27.0mm.

Frame looks same colour and design as this one but with blue forks as well (I havent got a decent pic yet, sorry)

http://www.ibikedb.net/bikes/34598-raleigh-special-products-853-road

Im really asking...is it 27.0mm or has it been forced from 27.2mm to 27.0mm? Anyone out there have the same frame to check?

I dont want to have it reamed just yet

thanks

you need an inverse shim and then the frame will be able to take the 27.2 seatpost

tynan has some for sale