I have both. The M4 is for looks. I don't mount a grenade launcher on mine. It takes more heat before shifting POI. My lightweight Bushy is awesome, very lightweight as is the rest of the rifle. However, it heats up really quick. I just plink with it though, no target or benchrest shooting, so I don't care. It's the rifle I would carry a lot and shoot little. The heavy barrel takes longer to heat up, but retains more heat when cooling down so it takes longer to cool. You must ask yourself, do you need to be able to shoot longer strings before POI changes then have to wait longer, or perhaps you will carrying it a lot. Each barrel has it's place, looks aside. The skinny barrel, when cool, can be as accurate as an HBAR, though the HBAR will whip less and can be conducive to achieving increased accuracy when trying handload.