Snap caps or dummy rds are useful to practice malfunction clearance drills. using a an empty casing that has already expanded in the the chamber at 52.000PSI will cause the casing to lodge in the chamber with the bolt half out of battery. you will try to charge the weapon to clear it and it will not budge. you will then try to crack the upper open and find it won't cause the bolt is halfway in the receiver tube.... to avoid all that, use a snap cap or a dummy rd. I use tthe M199 dummy rds I got from My Uncle Sammy and put one about halfway into a loaded mag so I can practice Type 1 malfuction drills. (Tap,Rack,Boom) or find a reloading friend to resize some case's and leave out the primer and the powder and then drill some holes in the casing to easily identify it as a dummy rd. cheap and if the "range grass" monster eats them... no major loss.