While I use and teach the mag support method, here is some insight as to why some old time instructors or instructors taught by old timers as to why they are against it.....
I do know that many old time military types were trained to use a classic prone position with the rifle supported and not rested on the magazine. So you will see some mil type instructors teaching it. I do know that the largest producers of instructors is the NRA and they still teach a full support and are against a rested mag support. I still take an NRA course every 3 years or so on my employers dime in order to keep all my NRA certs updated, instead of submitting ongoing training records and my own $50, but as of my last course that I repeated for the nth time being the patrol rifle course about 2 years ago, the NRA is still against the mag support for the classic reason of inducing failures with a rested magazine. So the full support prone is still widely taught out there.
I will also add however that I do teach a fully supported prone position because it can give added height to perhaps clear an object while staying prone. Also guys who are more barrel chested, wearing armor and a helmet which can create its own issue, often times have a harder time making the mag rest prone position work for them.

Bookmarks