Hey, I was working on my roommate's older steel Campagnolo (1980s maybe?) and the old Kalloy seapost (which was cut too short for him) was clearly marked 27.2 and was very loose to the point that tightening the bolt all the way still wasn't tight enough since it slowly slid down even after we wiped off all the grease.
He then got a cheap black, used seatpost marked 27.2 and it was way too big - as in a hammer was needed. It was one of those "grooved" ones that was gritty feeling that I usually think of for mtbs so we ended up getting another one, a Kalloy Uno, that was 27.2, but that was way too big also. It takes both of us and a lot of 3-in-1 oil to get it to the right position.
I was just wondering why three different seatposts of the "same" size would be all that different. Do alloy/steel cylinders shrink over time? I didn't think the really loose one we pulled off was that old. Also, are there any options to get one that would work - maybe something a little smaller? We were thinking about that, but didn't want one that was as loose as the original one that was supposed to be 27.2.