A Hornady modified case versus having a piece of brass, shot in my gun, drilled and tapped for the Lock-N-Load OAL tool, I always get much more consistent measurements drilling and tapping a piece of brass that's been shot in my gun and formed to my guns chamber. With the store bought Modified cases they always seem to be so undersized and kind of wobble around in the chamber instead of using a piece of brass that's already been shot in my gun it fits perfectly with no wiggle.
IMO, you're way better off drilling and tapping a piece of brass you've fired in your gun to use with the LnL OAL tool, I think you'll get much more consistent measurements that way.