I usualy carry my M&P with full mag. So I have 17rds(16 in mag, 1 in tube).
But I guess I could carry 17 in mag, and 1 in tube total of 18rds.

Never did it. Honestly I never thought about it. Strange, since I'm believe more ammo is better then more punch, but less ammo count.

Do you guys carry +1?