Mod Rewrite creating too many redirects

I'm trying to force my site to use HTTPS.

I've tried the simple option - using a redirect - but this creates too many redirects which I believe is caused by mod_rewrite being used lower down the page to remove .php from files when loaded
If I try to edit this then it breaks the removal of .php, I'm not too experienced with mod_rewrite so I don't know what else to try or if there's any easier methods