I wouldn't really know, my only experience with the American magazines is with a RH .243 that fed perfectly (later sold) and the one.22-250 mag that came with this LH rifle. Even that one worked fine for a while.
The problem as I could see it was a combination of the feed lips being slightly too wide at the front along with the tapered .22-250 case, that allowed the case to pop out prematurely, then the nose would drop and hit the breechface of the barrel. Feeding the round quickly didn't give enough time for the nose to drop.
I had read here on the campfire that it was okay to load the mag by popping the rounds in from the top instead of sliding them in under the feed lips, that the mag was resilient enough to withstand that for several thousand rounds so that was how I loaded it. The feeding problem started after a few hundred rounds like that so it would seem likely that the feed lips are not so resilient as advertised but I can't state that unequivocally, nor did I figure out why the 1st and 4th rounds always fed but the 2nd and 3rd rounds jammed. I can only say that the replacement mag that works measures .416" across at the front of the feed lips and the original that didn't work so well measures .423" at that same point.
But in the "lemonade from lemons" category, I've kept the original mag which should be okay with standard .308 based rounds and may use the presence of the magazine as future justification for buying a new LH .243 rifle to go with it....
