A smaller handgun could still reach levels of 130-140 decibels. A big 12 gauge or something like that could reach 140-150.

(Speaking in terms of power ratios:) Remember that the difference between 130 and 150 dB is actually 100 times the intensity. There is a difference of two Bels between those two values, so 10^2 is 100 (to account for the logarithmic nature). If you shot a very small gun (like a Beretta) that only registered 120 dB, then your 150 dB shotgun blast would be 10^3, or 1,000 times more intense as that (or 100,000,000 times more intense than the average conversation of ~70dB).

The moral of the story: always wear hearing protection when you go shooting or hunting!