Which caliber for Pumpkins?
If you are asking what you should use to stop charging pumpkins, then this is a question of stopping power.
Should you use small mass and high velocity (9 mm, 40 S&W) or high mass and slower (45 ACP)?
Frankly, I would suggest that handgun calibers are not marauding pumpkin stoppers (except for the S&W 500). I would use, at minimum, a 223, and at maximum, a 458 Winmag.
If faced by an attack by the Great Pumpkin and his minions, then all bets are off unless you have access to a 155 mm cannon.
Just trying to help.
Ron