I agree and I'm the 3rd party. The issue is a common one within the industry. We have to tune the single stack mags for our hunting rifles for the same reason. The problem is 300 PRC has the same case head diameter as 300 Win Mag and manufacturers assume that magazines for 300 Win Mag will also work for 300 PRC provided that the mag will accommodate the extra length of the 300 PRC cartridge.
300 PRC has less taper in the case than 300 Win Mag, so magazines set up for Win Mag often do not feed well and need feed lip adjustments in single stack mags even if they are long enough for the 300 PRC. We both shorten the feed lips and adjust the openings on these mags.
The AI AXSR mags with the plastic base plates compound this issue by being a double stack mag. So, the round stack literally binds on itself in the magazine because there is not enough room in the magazine body for the wider cases just below the neck. This is what prevents the round stack from popping up so that the rounds can be fed into the chamber. Instead, the rounds stick nose down and try to feed into the front of the magazine.
The reason that AI has the issue is that the AXSR was originally designed for the US military ASR (Advanced Sniper Rifle) solicitation, which at the time specified .308, 300 Win Mag, and 338 Lapua. As such, the magazines are desinged around those cartridge families. 300 Norma and 338 Norma still use a Lapua bolt face, so the 338 Lapua mags should run those well. 300 PRC while it uses a 300 Win Mag bolt face, is not the same cartridge and is not just a longer 300 Win Mag so there are issues running that cartridge in those magazines. AI probably assumed that since the cartridge diameter is the same and the magazine will accept the extended length of the 300 PRC that they were compatible.
I'm assuming that AI doesn't think there are enough users shooting 300 PRC or the problem is not widespread enough to warrant a revised magazine. It's a shame because after we upgrade the mags, they still run 300 Win Mag just fine. They would not need a proprietary 300 PRC mag.
We address the issue in 3 areas: 1.) We tune the magazine feed lips for proper function with 300 PRC. 2.) We tweak the magazine body to get as much room as we can for the round stack 3.) We install a new follower that moves the magazine spring forward to provide more pressure at the front of the cartridge to help with feeding.