Long guns are cash and carry, meaning you can buy them and take possession the same day. You’ll need a valid drivers license. You’ll fill out a federal form so the FFL can determine if you are a prohibited person. If you are not, the FFL will run an instant background check. If that comes back clean, you’re good to go. Regarding Maryland law, detachable magazines are restricted to no more than ten rounds if bought, sold or transferred in Maryland. Possession and use of such magazines is legal. They can be bought out of state and brought in.