We have a bomb shelter that's made of concrete. We're converting into a training facility with a heavy bag and a small shooting range.

We're putting in sandbags and plywood against one wall for the shooting range. There's a ventilator so hopefully that takes care of the smokeless powder.

The heavy bag is a little difficult to hang. How should I go about this? Would drilling four hooks into the ceiling be enough to support the bag and continuous training?

exactly how heavy is the bag?

What type of bullets are expected to be used? Sandbags + plywood may not be enough. I assume the concrete wall is load-bearing, i.e. it holds up the roof?

Exactly what kind of training is going to be going on?

As KOT said, what caliber guns? The W&C guys can tell you the specifics for what to use. You could always set the sand bags up outside and shoot them to see what they'll stop. Plywood isn't going to do much except stop small bullet frags from hitting the concrete wall. A .22lr will blast right through a 2x4, just for reference.
If you tell us it's for airsoft guns, then....

You should hang your heavy bag with bolts. These bolts should be either fastened with a powder actuated fastener, or with some type of drop in fastener/wing nut deal.

22LR

Heavy bag is around a 100 lbs

I would leave it as a bomb shelter, if I was you.

What is the ceiling made of? (For attachment purposes- can you drill into it, is it strong?)

Easiest way would probably be to hang bag with a chain attached somehow to the ceiling.

The ceiling is made of concrete. I can drill sure but I'm not sure how to attach the hook for the chain.

How thick is the concrete? If it isnt very thick then you could put in those toggle bolts that have the spring-loaded wings that are meant for attaching to hollow surface.

if it is thick, then you need an expanding wall anchor.

for either, get at least a 1/2 inch bolt so it will be strong.

Be careful in the us making a "training facility" could be considered an act of terrorism, so they will be watcing seeing how your post just popped up in a different color on the NSA monitoring system. Ducttape

Make a marijuana growing OP instead.

I already have such an OP in my own room :)