From the top
LH Compact 243 in a predator stock, rotary or 450 stack mags work well
LH Compact 308 in a standard stock rotary or 450 mags work fine
Compact stock with 450 mag locked in
Compact stock with no mag
Ruger Ranch 5.56 with mag (RS practice rifle bought due to form and Wy elk guide) wish they made this in LH.
Next picture shows bottom profile difference
Lastly as you can see Ruger changed the bottom design at some point to allow use of Rotary or Magpul mags with different bottom inserts. Spoke with Ruger CS before buying the predator stock and was told it wouldn’t work, tried to buy replacement from Ruger but were no longer available. Bought from a seller in Alaska for $50 to try and it worked fine, confusion may reflect different generations of the rifle.
This replacement supposedly allows you to use rotary mags in the aics rifle.