The MP5 doesn't have as much poop to worry about so it isn't as destructive. Use your best judgement based on whether or not you can feel the bolt/carrier hitting the buffer and endcap. With the full power rifles you get damage to the buffer but also the rollers try to pop out when the carrier suddenly stops as it hits the buffer. This causes bumps to form on the rails because the rollers start banging against them. You can see these dents pretty easy. The buffer damage and such requires you pull the butt off....
There are other locking piece angles for the MP5 so you can look and see what you're running and go to the next one down when you put a can on. If it fully cycles with the ammo you use the locking piece is ok.
Frank
