400 won't cut it for a GBBR. You need that for JUST mags if you want to game it. I would go WE if you were desperate to have a GBBR.
But man if you're just starting out get an AEG and some mags it's cheaper. GBBRS are is a rich man's game.
“We sleep safe in our beds because rough men stand ready in the night to visit violence on those who would do us harm.”
To those Rough men... Thank You.