02/25/12 - It was unfortunate that they altered this but I think they realised that the community wasn't that interested in playing coop for so long to unlock weapons. The last mission was XP heaven as you could basically stay outside the bank and let the AI keep sending enemy contacts out for you to take down. You and your coop partner could spend just over an hour doing that alone before entering and completing the mission to max out on the XP for the weapon unlocks :).

12/16/11 - that's right

12/25/11 - That's correct. No worries though, it doesn't take long to reach 160,000 and unlock them all.

01/01/12 - not an answer but getting 300k for the g3a3 originally still isn't difficult. play each map on every difficulty and your good to go