Buffer tube inner diameters?

[Sitting Duck]

Remove ya crane stock a sec

you might have the G&G stock tube with slits at the side making it a bit easier to pull wires to one side

pop in modest 1000 to 1200mah lipo then sort out wires etc....

They do a few types but this is what I mean...

 

[Sacarathe]

Yep, had it off a few weeks ago, it's that style.