I don't think its your bottle, I think GSI had screwed up for awhile and distributed a bunch of cups out that were a bit too small. I had found the same problem for a little over a year at Sportsmans Warehouse and also saw on the Bass Pro Shop site they had pulled the cups until GSI started getting out cups that fit. I started seeing ones that fit at Bass Pro again in March. I hope to find out if this is still true in a couple of weeks.I have not heard this issue pop up with the Olicamps, but then, I never see those in stores.