Is there a limit to how many enemies can be attacked using the Hunter ranger's Volley, Horde Breaker, and the second attack?

Question

From other questions on here, I know that both Horde Breaker and Volley can be used together, as discussed here: Do the Hunter ranger's Horde Breaker and Volley features interact?

Is there any limit to how many enemies you can attack using this combo if they fall into the 10-foot radius of the initial Volley?

Say there is a shield-wall type of formation of enemies, all nicely lined up side by side and multiple rows deep. In theory, based on the phrasing of Volley, you can use Volley to attack every creature in the 10-foot radius, potentially attacking 16 targets - and you can use Horde Breaker on any that are within 5 feet of the point of origin. If the origin is the middle of the group, then possibly 8 additional targets - and then use Volley again for your second attack as a Hunter, making 40 total attack rolls in this situation (assuming they are all lined up nicely). Is this correct?

In my current campaign, we have stumbled into a war-torn region where large armies of Orcs are massing (my preferred enemy), and I'd love to use this loop hole if they end up lining up nicely for me.

Answer 1

Yes, there are some limits you've missed

First of all, you can only use this once per turn, not twice. Using Volley requires an action, and you only have one action per turn (unless you have a feature that gives you an additional one, such as the fighter's Action Surge). Your Extra Attack feature is not relevant here, because if you took the Attack action, you wouldn't be able to take the Volley action.

Next, Horde Breaker can also only be used once per turn, so it grants at most one additional attack, not 8.

So, if creatures are packed tightly into a 5-foot-square grid, Volley will get you 16 attacks¹, and Horde Breaker will get you one more, for a total of 17 attacks. It's still very powerful against clumped up enemies, but not as powerful as you were thinking.

As a side note, the one attack from Horde Breaker doesn't need to be within 5 feet of the center point of the Volley's area or even within the Volley's area at all. It just needs to be within 5 feet of one of the creatures you attacked with Volley. This can include a creature that you already targeted with the Volley (in which case you would be making a second attack against that creature), or it can be any other creature adjacent to one of them.

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¹_{I don't have a grid in front of me to check whether 16 is the right number for a 10-foot radius, but I'll assume it is.}