I see nothing wrong with rolling a shell to get it to fit.. To be honest, think about how a shell is made, when the two hemi's are pushed together, sometimes you have to beat it with a mallet to get...
I remember that video where they were handling shells while smoking.
To this day, I'm still horrified they were doing that.
You could always try the shell in a different mortar first. It might be the mortar that's a bit malformed rather than the shell.
Oh hell no that's what burn piles are for. Often one of the best parts of the night!