You could try it, but I highly doubt it will work.
The .223 mag's have a spacer block in the back of them which you wouldn't have in the bottom extension. You could add a matching block easily enough I suppose, but then you run into the second problem - the internal width of the extension. They're machined out for .308 sized cases and the .223's are notably smaller in diameter which would likely result in stacking issues that would lead to feeding issues.
If you look at the followers they have notches in the sides to match the indentations in the side of the metal magazine housings. This is what helps to keep them level both fore and aft as well as side-to-side. Those same indentations in the housing are what aligns the cartridges to stack properly to ensure proper feeding.
Bookmarks