That cock'n'balls shaped BB bag I mentioned earlier is my solution to a few problems with those bags ppl make for fleabay. The main one is that a soft bag is fuck all use for pouring BB's b/c wherever you hold it with one hand one end is hanging down - either the bottle neck 'spout' making a bid for freedom, or the bag holding the BB's below so they aren't pouring. You can just about wrangle a handful inside the bag, but it's not as quick and easy as you want if you're doing it in the field under fire/taking time when your team need you.
Most hi cap mags or speedloaders have a hatch that is too small to pour straight into from a bottle neck, but if you constrict a BB container spout much more than that the BB's jam up against themselves so then you have to shake it, making a noise and taking yonks as they only pour a few more before jamming again. Best bet is to hold the mag/speadloader in one hand with the crook of your thumb wrapped around the opening acting as a funnel, which allows you to pour straight out of a bottle neck without any bother.
But a bottle rattles, hence using a bag, right? And a bag is awkward to pour from... How about both? More of the bottle than just the neck & lid so it adds a bit of structure to the bag which makes it easy to pour from, sort of a scoop shape with the bottle cut diagonally from the shoulder and whatever size/shape of bag you like/can sew underneath that. To stop it rattling I used that thin white packing foam wrap stuff cut to fit exactly and glued to the inside of the bottle. I then glued the outside of the bottle to the inside of an old Norje sleeve and stitched through the bottle and cloth to make sure. I would say it's the dog's bollocks, but you can see that it's actually the donkey's cock and bollocks
That shape came about purely by accident because I wanted the bottom to have the same footprint as a Crusader cup, so it would fit neatly into a PLCE canteen pouch. So I turned the cup upside down and drew round it, added a bit for the seam and sewed it. Obviously using a sleeve gives it a foreskin, but it's the simplest way to go about it - a sleeve is already exactly the shape you need to fit a bottle into. Tip: be careful not to over-tighten the lid - it's easily done and it makes the top disc pop off the threaded part of the lid!