Fastest way to level weapons

So, I was going into a solo/co-op game to drive some tuk-tuk around with my friends, just having a good time. Now during the match I notice a small but quite effective method of leveling weapons. I tried it again solo and jupp. fastest way of leveling weapons is definitely Breakthrough with bots. So I did this on solo, no one but me and them bots. I have the bots on advanced but you probably could do with any difficulty.

So when playing with bots the objectives are a little different then multiplayer. But  On the map Kaleidoscope you will still end up with the last objective being on top of the building, just like we all love and hate in multiplayer. Now, bring some ammo, and preferably a LMG or assualt rifle. 
Once the you get to the last objective, the same amazing phenomenon as we see in multiplayer will occur. Exactly! you will find the object being infested by some 30 bots and your best bet would be to run and hide behind the elevators. Now from here you can throw your ammo down, and start shooting over the pipelines, while it rarely happens, the bots can still kill you. I did this twice and got all attachments for my LMG, with about 350-400 kills each round. Enjoy!