I know you all have used this gun while camping, but I'm here to tell you how to get the most out of the gun.
1. was a glitch - deleted by AL
2. Have faith in the Desert Eagle. Plain and simple. Everyone says it's so inaccurate and a piece of crap but you have no idea how many times I've gotten those "lucky" shots far range with it. It will SAVE your LIFE many times.
3. Find a high traffic place where you can easily pop out on someone. The M3 is extremely good upclose, therefor if you can pop out on a unsuspecting SEAL with a 1-2 shot kill gun, you're going to get a kill.
4. Never never never never charge someone midrange shooting like an idiot. They almost always will back up and kill you. I've had some pretty long distance shots with an M3 but you are so much better off sneaking up on them or waiting to get a close up firefight.
5. Take advantage of laying down with an M3. At levels such as fish hook, you can go to the right breach and lay down and when they come to plant C4, you can shoot their feet in 1st Person and kill them under the breach. Another place in Fish hook is at the top of the stairs in the hostage building. What used to be a common place, people stopped going there because they keep getting killed from the corner downstairs, but if you lay down upstairs they'll just waste their ammunition hitting the wall, or better yet a hostage.
6. My last and final tip would be to run away if the SEALs are afraid to get close. There's no shame in it, why take an inevitable death when you can just run and hide, waiting for them to unsuspectingly run by. One instance where this is useful is in hostage levels. If they are shooting long range and you have the hostages, stay near them and run away behind them, the SEAL will kill hostages thus giving you a win.
Hopefully you can get some tips out of this and quit calling the M3 a newb gun.

There's more things than just camping with it, it's useful in many different levels.