To achieve peak performance with this Sig Sauer Scorpion BB air pistol, we recommend using SIG SAUER or equivalent premium pellets with a grain weight listed below. “Blowback” models closely mimic the operation of a semi-auto firearm. When fired, the slide or bolt recoils which generates a felt recoil impulse and, on most models, recocks the hammer which provides a more realistic trigger pull. Blowback Airsoft and Airgun models which fire BBs will often have a functional Last Round Bolt Hold Open so that the action will lock to the rear once the magazine is out of BBs. These models are very entertaining to shoot and are excellent training tools since their operation is so close to a semi-auto firearm.