Here's a copy of the write up I was talking about:
"Thought I would do a little mag comparison for anyone wanting to know what some of the other mag options are and how they compare.
The P MAGS that come with the rifle are nice if you are shooting factory ammo. They will not hold some of the longer hand loads, which was an issue for me. The P Mags are very easy to load and are fairly compact. However, they do not slide into/out of the lower as easily as other styles of mags. They mag release has to be pressed a little harder and further to drop a P Mag than with other mags. If you attempt to cycle the bolt with an empty P Mag, the bolt hits the follower in the mag and roughs it up. Top loading with a P Mag is very difficult. You have to slide the round into the camber with your finger before you can close the bolt.
AI STYLE MAGS hold longer rounds than the P Mags do, which is why I bought one. Unfortunately the mags are quite a bit longer than the P Mags and the ARC mags. They are a little harder to load than a P Mag. These mags slide into/out of the lower very easily. The mag release does not have to be pressed very hard to release these mags and they drop out on their own which is nice. The AI Mag has the same issue with top loading as the P Mag. You have to slide the round into the chamber with your finger before closing the bolt.
ARC MAGS are my personal favorite. They are short like the P Mag and hold longer hand loads. The ARC mag slides into/out of the lower very easily as well and releases easily with the mag release. These are the only mags that I have been able to successfully top load with. you can drop the round and top of the mag and close the bolt without any jamming or other issues. You can also buy a 4-round mag extender for these that makes them as long as the AI mags, but they hold 14 rounds, which can come in very handy on 12+ round stages if you don't want to do a mag change or top load.
I also purchased one of the polymer AI style mags from Ruger but I sent it back when I realized it wouldn't hold long hand loads.
All in all, ARC mags are the best all around mag in my opinion. Obviously everyone is entitled to the own opinion, but I hope this helps.