I’ve been using the ESSTAC KYWI pouches for both pistol & rifle for the past 6 or so years without issue. 3x Tall M4 on my PC and 2x pistol on my Batbelt with a single short M4 behind them (also can hold 2x pistol magazines if you’re just doing pistol stuff). With a little heat you can adjust the tension to whatever works for you.
The ESSTAC's have become the most popular thing with our guys going through CQC School as well, it's one of the few things you still see guy's buying out of their own pocket anymore as most of the gear issue otherwise has gotten pretty decent. ESSTAC pouches and inner/ outer shooter belts are the two things that are regularly purchased though. The only time I've ever had any issue with one of mine is when I got lazy and tried to use the double stack pistol mag pouches already on my belt to hold 1911 mags, they will do it on a square range but not if you are going to be moving a bunch, use the right pouch though and no issue. Never lost a mag with these to the tree's or vines here or in Okinawa and both places have plenty of veg to steal all of your stuff, I have occasionaly lost a mag with HSGI Taco's but that typically only happens once the pouch has become rather worn...
"So strong is this propensity of mankind, to fall into mutual animosities, that where no substantial occasion presents itself, the most frivolous and fanciful distinctions have been sufficient to kindle their unfriendly passions, and excite their most violent conflicts." - James Madison, Federalist No 10
My opinion about open-topped pouches is completely reformed. Thanks guys.
I had a custom kydex pouch made a few years before I retired. It was a double pouch mounted horizontally with mags placed bullets out. The retention was decent but I took a small ball bearing and heated up the kydex then pushed the ball bearing in where the magazine catch notch was for this purpose. They weren't coming out without a real pull.