Shouldn't the modified case be the same as a full length resized case?
That depends on how you size your cases. Properly sized cases should be .001-.002 shorter than your chamber.
The modified case is sized by Hornady to SAAMI minimum length.
My sized cases are all slightly longer from base to shoulder than the modified cases.
Take a permanent marker and color the bullet on one of your rounds. Chamber it carefully and extract it. Check if the rifling has scratched off the marker. Even if it does, if you start at minimum and work up, you'll be safe but pressures will be higher than if the bullet wasn't seated in the rifling.
Still happily answering to the call-sign Peetza.
You do not HAVE a soul. You ARE a soul. You HAVE a body.
He is no fool who gives what he can not keep to gain what he can not lose.
-Jim Eliott, paraphrasing Philip Henry.