I've never played MW2, so I have no fuckking idea what you're talking about.

I can realate to the P90 and the M16. Those guns in MWR are stupid. People go around spamming P90 and M16 is way overpowered. M16 sometimes is one burst, you're dead. That's horseshit. Talk about no skill. Then people attach Tubes to it. That spells out noob. You can get tube on all of the Assualt rifles. I'm guessing it's the same for MW2. Honestly, I think boom is the last thing you unlock, not first. You should learn the game without the aid of explosives. FFS use a gun.
/rant
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Also, in MWR I only use slow guns. Such as Snipers and Shottys. If I need to get myself out of a pickle (lol) I'll bust out the 74u. Which is a legit gun.