Don't use the Lord's name in vain. needs Help

My 2nd CO who is also my second sniper and a medium rifleman which he also sometimes fills the role of DM and heavy gunner. His Codename is Don't use the Lord's name in vain. and he needs help. first off hes stubborn and belives all of his weapons are the same qaulity of a systema. But in todays game his JG m16 A3/A4 died on him. Now hes turned to me for help to find a gun that will last minimum of 4 years.

To get down to it he wants an M16 a G36K or an AK 47 that will be able to be used as a
DMR
A medium riflemans rifle
(ie able to hold basic optics and a grenade launcher)
a heavy gunner
(ie a box mag c mag drum mag ect ect.)
He dosent care about weight hes a BIG guy a SAW is where he stops weight wise.
It has to be above 350 stock fps and his defenite budget is $200 he might be able to go up to $500 only if he has too. Hes not into internal upgrading so as a DMR it needs average range.
The JG G36K with the rails is what hes looking at and the Echo 1 Stag Arms A3/A4.
He likes M16 the best with g36s at a close 2nd.
Help?

There are NO guns on the market that will last 4 Years, without doing the maintenance on them !!

If you are Playing every weekend, Putting a couple thousand BB´s through the gun, and not doing the extra work to take care of the gun, you will be lucky to make it through 1 AS season without any problems.

Well my Swiss arms M6 did 4 years just had to clean and lube it and it did me just fine. G ods JG m16 lasted two before it had an issue and he plays year round. Its like I said he treats it like a systema so he never really has gun issues.

Maybe I should rephrase this whats the best rifle that is a g36k an m16 and an AK and is under 200$ and if thats impossible to find $500 is stopping point.