Slow motion makes everything look cooler, including fiery shotgun blasts.
Whether you're in love with Wes Anderson's slow-mo final exits or Neo's bullet-time contortions in The Matrix, I think it's safe to say that slow motion captivates audiences by altering time in a very unique way. And the faster the real-time action, like a blink, a balloon popping, or a lightening strike, the cooler it is in slow-mo, which is why this tutorial from Film Riot is awesome, because it shows you how to add slow motion gunshot effects to your footage—and actually make it look real!
Once you get yourself some digital assets, like muzzle flashes, smoke, sparks, particles, dust, etc., you can head into After Effects to get to work, and host Ryan Connolly does a great job of walking you through the process step-by-step. Keep in mind, though, that if you're not all too familiar with working with visual effects, you might want to save the more advanced slow motion element for a time when you feel more comfortable with adding basic assets to your real-time footage. (Unless you're a beautiful daredevil, in which case you're definitely not even reading this paragraph because you're busy throughing caution to the wind and riding this tutorial bareback. Good for you.)
Now, post-production is not the only way to get gunshot blasts. You can use squibs and blanks with real guns, but not only can those effects be dangerous, you'll end up spending quite a lot of dough to hire professionals to make sure you're not using them like a knucklehead. That's why the option to add some gunshot VFX in post works for a lot of people, especially those that wouldn't even know where to look to hire a SFX supervisor. The rub, though, is making sure your effects look realistic and are believable—you can learn a few tips on how to do that here.