The 25+ kills with each weapon for this achievement tracks across both single and multiplayer games.
If you complete single player and still don't have the achievement you can boost weapon kills on your own with a second controller.
Set up a Dog Pile game with a guest account (in a lobby press A on the 2nd controller when it's switched on and go to guest at the bottom). If you play Dogfight you'll get a lot of random people joining you whereas with Dog Pile it's less likely.
In the lobby select the 'progress' option and go to achievements, then Weaponeer. It will tell you how many kills you have with each weapon. Choose two weapons you need kills in before the match starts. I always went with at least 1 homing weapon for the long range kills. I used the light plane as well so I could fly around faster (and also to match their speed easily!).
With the second controller make sure they have a light plane (easier to kill).
If you choose the Sand Sphinx map then it's smaller and easier to find/get to the other planes
without them going off-map (which is an easy way to get assists if you need them as well).EMP:
Just fly close then let rip. Easy kill.Mines (BAM, Squitos):
Fly alongside the guest then use your turbo to get just in front of them then start laying. If a couple of seconds pass and no explosion, try again.Non-Homing Weapons:
Fly close behind the guest. Fire away until they go down.Homing Weapons:
Find out where the other planes are and get them roughly in your sights. Fire until dead.
If you don't have a second controller (friend willing to leave their game running for you) then play through some of the easier solo missions, specifically using the weapons you need kills for.
If you're going to try to get Flying Ace as well, pick up the Bone. It'll end the match after 2 minutes but you'll get a lot more xp and you can keep playing it over and over for the weapon kills.
See my guide for that achievement for more details.Solution for Flying Ace in Snoopy Flying Ace