This is a quality piece of kit, but the partitions inside are not sewn all the way to the bottom of the pouches. My Magpul polymer AK mags are a tight fit, which isn't the worrisome part. The partitions inside are, however. My mags get hung up on the bottom of the internal partition whenever I put them in right side up, or upside down.
There internal mag pouch partitions create a large part for the mags, and a smaller space in front of those.
To be honest, nylon, no matter if it's 500 or 1000 denier, don't hold water very well. It let's it drain out pretty easily in my experience. Though if you have to have them, put two in, sew the internal mag partitions all the way to the bottom. Or just don't put the internal partitions in at all. I don't understand why they're even there in the first place. These would hold the mags great even without them.
The straps hold the magazines great and it's, overall, a quality product. However, I'm seriously considering cutting the internal mag partitions out with scissors. The smaller, forward space can hold pistol mags, but when I go for the rifle mags, the pistol mag drops down into the pouch and makes it difficult to get out.
It can hold 40-rounders but the straps don't secure. But that's been my luck with any kind of pouch, even taco shells.
So, for short, good job except for the internal mag partitions.