Since the patch Backpack Mastery gives only 1000 Inventory capacity. I think its definitely too little.
Seems like the Item-Weight has been reduced too, but i think it doesnt suit. Having few Bullet-Stacks in the inventory and i am overloaded.
In addition Bean Bullets do not have Weight 0.
I think that has to be changed again.
Bean Bullets ---> Weight 0
Backpack Mastery giving 5000 or sth like that