First off, if you are making a dump pouch, make sure it is completely over engineered on the seams. The point of a dump pouch is so you don't lose your mags, and it would be a problem if your I-don't-want-to-lose-a-mag-pouch had a hole in it... :lol:
For size, just go with something that can hold all the mags in your rig (primary and secondary) plus a little extra space (if you play an objective based game and have any game items, it's easiest to drop small items into your dump pouch instead of unzipping a utility pouch). I had style dump pouch at one point, but I never used all the space and found that the pouch took up too much room on my gear, so I downsized to . At absolute most I run five rifle mags and three pistol mags, and that pouch holds them fine.
As for rattling around, it depends on what you run for a gun (or guns). Whenever I drop my M4 mags, I always do it the same way, so the mags stack side by side and don't rattle that much. However, if I am running my GBB MP5 I find that since the mags are smaller and heavier, they flop around a bit more. It's not really loud, but don't make the mistake I did and try to sprint with a dump pouch full of gas mags if you run your dump pouch low and relatively centered on your gear. No man wants to have a large bag of metal blocks swing into his groin... :oops:
"Airsoft is a game, and it is a game in which honesty, integrity and honor play a very important role. This is not paintball." -NEASG Rules
I make custom Kydex gear. See some of my work or email granitestateguns(at)gmail.com
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