The 223 action may not extract and eject a 20VT case very well. I'm turning my .223 into a 20 Practical when I feel the barrel is shot out. That would be my recommendation.
I'm curious, why the AR magazine? If I had 30 rounds available I'm afraid I would roast my barrel. Best for me to only have 5 rounds at a time, so at least during the reloading of the rifle it has some cooling time. For varmint hunting I have at least 3 rifles in rotation - 5 shots and then swap out for another rifle to make sure the barrels cool.
I'm curious, why the AR magazine? If I had 30 rounds available I'm afraid I would roast my barrel. Best for me to only have 5 rounds at a time, so at least during the reloading of the rifle it has some cooling time. For varmint hunting I have at least 3 rifles in rotation - 5 shots and then swap out for another rifle to make sure the barrels cool.