ShootingTheBull410 (one my absolute favorite YouTube channels) has tested the SS197 5.7 x 28mm projective in his characteristic ballistics gel test. Tested out of the FiveSeveN, the SS197 comes in between the 22LR and 9mm in terms of ballistic energy. Combined with a ballistics tip and extreme velocity, one would expect the terminal results to be fantastic…

Nope. Four of the five rounds fail to achieve expansion (likely a result of low velocity). With one round expanding and others showing some signs, the pistol is just on the hairy-edge of effective velocities for the bullet design. Logic would dictate that the round would perform better out of the PS90 with the higher velocities.

Those carrying the FiveSeveN may want to look at another round for ever-day carry.