I think while well intentioned this video will not be applicable to most users. The ease of clearing you demonstrate is due to unique design quirks of the SafeMag.
The SafeMag is tuned during install to the magazine and body of the receiver like the picture below. Therefore the upper only needs a little play to drop the mag. Every other fixed magazine solution requires much more play and the mag will still be lodged in place.
https://youtu.be/5m4K0cqJ2Z4?t=50s
https://i.ytimg.com/vi/dzkXLlCDKgI/maxresdefault.jpg
The main problem to clearing a doublefeed, with a fixed mag at least, is getting the feedlips and jamming rounds out of the path of the bolt carrier group so it can move forward, enter battery, and clear the buffer tube so you can disassemble the upper. Normally this is done by just dropping the mag. Duh. With any other fixed system the feedlips would still be there trapping the rounds. You can at least solve the rounds by dropping the floorplate. Except the retarded laws tell you to glue it shut.
When you try to slide the upper forward with the mag still in place, the rectangular magwell cutout in the upper will slam into the magazine feedlips from behind jamming it. The rounded cutout in the picture below. No further forward motion is possible and the bolt carrier will still be stuck in the buffer tube.
https://www.cmttac.com/image/cache/data/UHP-UR%20AMMO%20GRADE-800x800.jpg
Believe me, I've tried this with an armaglock and it was a giant pain in the ass. A lot more sliding and jimmying is involved. If you could repeat this video with that or the patriot lock it would be a lot more helpful. I'd upvote the shit out of that guide.
