If any of these don't say 25/25 or 100/100, it simply means you have missed out getting the achievement because the X amount of kills haven't been met. And then the final weapon requires you to get 100 kills as well as earning the last achievement.
Each of these weapons require you to get 25 kills to unlock another weapon & the related achievement. Press the button and select Loadouts and then press the button on your Man-at-arms class until you see a selection of weapons to choose from.Now if the worst was to happen and the game doesn't give you the achievement once you have met the requirements, then there are some methods you need to apply in order to try to get this achievement fixed. Getting kicked could possibly place a fault in the game and glitch the achievement. When a match is completed, make sure that every individual player in the match leaves the game themselves rather than being kicked by the host when they end the game.The only time you should switch over a weapon is when you unlock the two related achievements for the weapon you are working on and need to choose one of the other remaining weapons within the class that has achievements tied to it. Stick with the weapon you have been using to unlock the others. Don't switch over to any upgraded weapon within this class.Once you have successfully obtained the achievement, swap over and let your partner work on it. Don't let your partner jump in whilst you are half-way into getting this achievement as this could possibly glitch the achievement for yourself. If you start working on this achievement, make sure you go forth and complete the requirements and get this achievement unlocked first.You can work on a couple misc achievements along the way as the Story Walkthrough will direct you, but don't go out of your way and choose a different class or a different game mode until this achievement unlocks. Start working on the Man-at-arms class first and do not start working on the others.These game modes could muck up the achievements progress as well as cause other faults. Do not play the Training or the Single Player game modes.But make sure you resume whoever was working on the achievement instead of someone else starting to work on it. If however your console should freeze and you have to restart it then this shouldn't be a problem. Until you and your partner/s have both got this achievement unlocked, as soon as you start-up the game, do not exit the game and return to the Xbox 360 Dashboard and do not turn off your Xbox 360.Now if you are planning to start-up this game for the first time, then there are some recommendations you should go for with you and your partner in regards to this achievement. Unfortunately there is a possibility that the achievement may not unlock at the same time and if it doesn't, you have a glitch and you need to try and resolve it as soon as possible. As soon as you have claimed your final kill with the final class you are working on in the Man-at-arms class, not only will you unlock the achievement for the final 100th related kill on the weapon, but you are supposed to unlock this achievement as well for completing all of the weapon requirements and unlocking all of the additional weapons for the Man-at-arms class. Originally the achievement is meant to unlock once you have completed all of your kill requirements for the Man-at-arms class.
Since the games released the Xbox 360 Version of Chivalry has never had an update and as such this achievement is known to be Partially Discontinued/Un-Obtainable if the requirements are not met correctly.