I recently did a series of blog posts about putting together canvases.
One of the things that drives me crazy when stretching a canvas is when the wood is so hard that the staples get bent right out of the staple gun. This DRIVES ME CRAZY. I then have to turn the gun sideways until I find an angle where the wood will take the staple.
I wasn't using bars that bend the staples when I did my blog posts, but I recently pulled a canvas off bars and restretched and...BENT STAPLES!! Aaargh! However, I took some photos so you can see what I mean.