Technically the PKM, since it is an AK-47 variant it fires a 7.62mm round while the M249 shoots a smaller 5.56mm round
the legendary Pokemon you can catch in pkm d/p is dialga (diamond), palkia (pearl), cresselia, regigigas, heatran, arceus (event pkm), darkrai (event pkm), shaymin (event pkm) , azelf, uxie, mesprit. and giratina
The Kalishnikov PKM is a gas operated, belt fed, air cooled, automatic only, machine gun.
cheatcodes
The M249 Squad Automatic Weapon fires the same 5.56x45mm cartridge used by the M16 and M4.
Phycic pkm are super effective against fighting pkm. and flying larson
The maximum effective range of the M249 light machine gun is 1,000 yards (910 meters).
CLP
FN Herstal
In short the M249 is effective up to 1000 meters to cover an area target which the gun is designed to do.
$2150 USD in 2014
700-1200 rpm.
ANSWER:You need to use a GBA Link cable and trade the PKM you want to trade/ evolve into another PKM LeafGreen or PKM FireRed game cartridge.Next time make it into an actual question, not a question that is missing alot of information" Trading Pokemon on Pokemon leaf green?" yeah what about it though?