I bought a 1/2 inch end cap fitting from home depot today and a 10 ft 1/2 inch copper pipe. when I got home and tried to insert the pipe into the fitting it wouldn't go in at all. after struggling with it for a little while, reaming the inside and the outside of the pipe for 20ish minutes and making sure the pipe was as round as possible I was able to get it to go into the fitting, but it was still really tight. I tested the end cap on some old 1/2 inch copper that I had lying around and there were no issues at all.

I went to a different home depot and tested out the endcap and a few other fittings on other pipes they had, they were impossible to press on with both 1/2 inch and 3/4 inch pipes. Am I doing something wrong here? I can't imagine plumbers are sitting there for 20 minutes for each fitting. Or are home depot's pipes just bad? the brand was mueller industries, streamline. it looks like that is what lowes and ferguson carry too.

Outer dimension of the pipes from my non digital calipers looked to be a couple hairs over 5/8 inch