Agnotology
NES Member
I guess I don't see the advantage. Three extra rounds versus a G17 which is the same size. When I lived in NC nobody I knew owned one or carried one, and down there 60% plus own guns. If you're worried about soft armor and can get the magical AP ammo I guess, but I will keep my G19 with 15+1, a 19 or 20 round reload and hornady critical duty.
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You have about the same amount of energy in either round. If you want to compare hotter or heavier loads in 9mm, we can match that up against hotter and heavier loads from the 5.7, although the options are more limited because of ammo availability. If you want a 19 or 20 round mag in a G17, you can extend the baseplate in a FN 5-7 to increase capacity. (or a M&P 5-7, or a Rock 5.7)
The biggest downfall for the round is the cost of ammo, and it's a self sustaining problem. People see ammo prices and balk, don't buy, not increasing demand for the ammo which keeps production volumes low.