This achievement is for prestiging with 25 weapons or getting max level with 25 weapons in zombies.Here is a list of all weapon max levels so you don't have to end a match to check whether or not you just got max level with a gun.If you fulfilled the requirements for getting 25 weapons to max level or prestige 1 before the achievement was fixed, you likely will need to get another weapon to max level or prestige one or you could try and prestige a weapon you have at max level.Personally, I have been trying to avoid any weapon that doesn't allow you to put on attachments. This is because as you unlock attachments for guns that have them, the weapons themselves because very powerful and it also feels good when you are actually unlocking something rather than leveling weapons that don't give you anything for doing it. Avoid the Essex Model 07 at all costs! I wasted my time with this weapon but it is absolute trash. Hands down, worst weapon in the game. Also, you can't get levels for wonder-weapons so avoid using those when going for this achievement.Here is a list of level unlocks for zombies in case you forget which weapons you have unlocked mid-game:weapons you unlock by leveling up in that match cannot be leveled up until you end the game and start a new one. Keep track of what level you start at when you start a match so you can work on the weapons unlocked at that level.Now into the actual strategy guide for leveling weapons quickly. I have a DLC strategy and a base game strategy. Both work fine. If anyone is interested, my perk setup is quick revive, death wish, dead shot for weapon camos while leveling the guns, and stamina up for training on the roof of blood of the dead as my modifier.XP earn rate is similar in all games with 1-4 people so play solo for the most zombie kills per round. Hardened difficulty earns you 125% the XP you would earn while playing normal or casual but I recommend playing casual because zombies have less health and this will make a difference on the higher rounds. Also, on hardcore you only have 150 health.TLDR: Personally, I always just train on the roof of Blood of the Dead on casual difficulty until round 60-70 and then I end the game.Basically, you just want to survive until the zombies take too much ammo to kill (round 50/60 on casual) and get as many kills with your guns that you are leveling as possible. Just keep track of what weapons you have unlocked and what the max levels are so you know when you've maxed a gun and you can pick up a new one. If you wanna train on Classified train on the bottom of the war room level. If you wanna train on IX train in the starting room. If you wanna train on Blood of the Dead train on the roof. If you wanna camp you can camp at the top of the stairs at the warden's house in Blood of the Dead or you can camp in the elevator with one bot on Classified.This might be patched later cause it's kind of a cheese spot but you aren't glitching or anything while using it."On IX, there is a kind of "cool spot" for headshots, check here > https://www.reddit.com/r/CODZombies/comments/9tg0sc/does_any ...