With regards to naming, there are a number of different options I could see - 'load' and 'reload' could both work. I'll suggest 'arm' as another option.
I'll note that there are also a few design tweaks you could make - you could have it be 'load 1' / 'load N' if you want it to be more flexible. You could also have it create artifact or enchantment tokens that can be sacrificed. You also could put the counters on the player instead of on the emblem - I'll note that proliferate can only put extra counters on permanents and players, so you can't choose actually choose an emblem. You may still need to grant the emblem though.
With regards to power level... fairly high, I would say, but also very contextual. In EDH? I probably wouldn't be that excited by it - 1 damage isn't enough to kill anything meaningful. But in Draft or Standard? I would value this pretty highly. In a vacuum, I would say a single bullet counter is roughly equal in value to a single Clue token, and stronger than a Food token. They also look roughly comparable to the Rock tokens from
Toggo, Goblin Weaponsmith - 1 mana for 1 damage is roughly equal to 2 mana and a tap for 2 damage. I do think it is weaker than 2 mana to deal 2 damage (with no equip / tap) though.
In general, I would be concerned about this mechanic showing up in large quantities - it adds a lot of design constraints and board complexity. X/1 creatures become an immediate liability, and it makes combat math very complicated. The ability to hit players can also lead to some undesirable game states. I would highly recommend limiting activations to sorcery speed, which reduces board complexity significantly. Beyond that, I could see keeping the activation cost at
or bumping it up to
depending on whether you want it to be closer to Food or Clues in power level. Either way, I don't think you want something like Gallant Gunsman at common that is capable of triggering multiple times.
