It's not clear, but it sounds like you are letting the players call out moves instead of letting them trigger from descriptions.
Apocalypse World breaks badly when this happens. It's playing the game backwards.
The AP ammo works exactly as you describe, yes, and doesn't break anything. Gunluggers are absolute beasts and they will wreck anything they point their gun/anger at. This is fine and doesn't cause any problems by itself. (Well, not rules problems. It may cause the Gunlugger “poor life choices” problems.)
But Apocalypse World doesn't just let players do moves whenever they want. They have to work for them and actually do the trigger, not just say the move. If you're letting your players call out the moves, as if they are D&D 4e powers, then the game is breaking, and you will wonder how the Gunlugger isn't totally overpowered.
For example, you can't seize an entire hardhold by force just by saying “I seize the hardhold by force.” That's like saying “I seize the Moon by force” — it's not going to happen just by saying so.
The player can't (i.e., is literally not allowed by the game) to just name moves. Nothing happens just by saying a move. Instead, the player has to actually describe their Gunlugger doing real things: running up to the hold, sniping people on the top of the wall, charging the front gate, throwing explosives, opening fire on a whole mob of hold citizens, throwing grenades at the hold's gang, headbutting the giant wearing car doors for armour, shoving their assault rifle in the hardhold leader's face, and shouting “YOU ARE ALL MINE NOW”.
Maybe, at that last moment, the character has touched the trigger for seize (the hold) by force and the player is allowed to roll for the move. (Of course, many, many other moves would also have triggered on the way in. Possibly even some other seize by force moves, seizing smaller, more concrete things like people or defensible positions. It would have been an utterly epic event, assuming the Gunlugger survived the whole way.)
Go back to the Basics (2nd edition, p. 10) and review the most important rule for how moves work:
The rule for moves is to do it, do it. In order for it to be a move and for the player to roll dice, the character has to do something that counts as that move; and whenever the character does something that counts as a move, it’s the move and the player rolls dice.
So when a player says “I seize the hold by force!”, your job is to say “Cool, okay. What does that look like?” so that the player has to actually say what the character is doing. And if what they do doesn't trigger the move — no move happens (same page, emphasis mine):
Usually it’s unambiguous: “dammit, I guess I crawl out there. I try to keep my head down. I’m doing it under fire?” “Yep.” But there are two ways they sometimes don’t line up, and it’s your job as MC to deal with them.
First is when a player says only that her character makes a move, without having her character actually take any such action. For instance: “I go aggro on him.” Your answer then should be “cool, what do you do?” “I seize the radio by force.” “Cool, what do you do?” “I try to seduce him.” “Cool, what do you do?”
Eventually, maybe a move happens, but in the meantime, the character is doing things, all kinds of things, and the game is there. The gameplay is not pushing moves like buttons, it's everything that happens around the moves.
So yeah, the Gunlugger can wreck things and the AP rules make them able to wreck some really strong things. This is normal, and it's part of why the Gunlugger is worth being a fan of for the MC. But Apocalypse World is not a nice place, and carelessly doing angry things to it doesn't always go well. If the game isn't being played backwards, then the Gunlugger will eventually upset or break someone or something that can't be solved by shooting it, and suddenly things will get very interesting.