I got my first SPR cut for AICS mags and used PTG bottom metal. I have tried AI, Accurate Mag, and Magpul. They work, but poorly, and the rifle is a push feed with them, so chambering isn't smooth and great like an SPR should be. Oh, and I tried one of those short ARC 10 rounders, too. It couldn't feed a single round.
I went to a Mcree chassis, assuming it was the fault of the PTG bottom metal. It is the same fitment to a thousandth and the same result.
The FN DBM or TBM is the way to go.
I tried to work with CDI but their bottom metal didn't work. It was very, very, very poor quality. The owner of CDI said I had to hold the mag at a certain height to get it to feed. I forget how much slop the mag had up and down, but I remember it was more than the diameter of a 308 case head. So I would have had to look into the actiom, raise the mag to the right height, then hold it there to work the bolt. The owner stole a "restocking fee" from me and I had to pay shipping to return the stock he ruined. I have nothing nice to say about CDI after my only interaction with them.