Here goes:
So the external magazine dimensions are the same between a 308 AICS magazine and a 223 AICS magazine....for the most part...with some differences in specs from one brand to the next.
HOWEVER. You will have one hell of a fun time getting an AICS 223 magazine to feed a Ruger American 223 in the Magpul Hunter stock.
Here’s why: Magpul has their very own specifications to which they build the Hunter stock and their own 308 magazine. When you put any magazine NOT made by Magpul into the Hunter stock, it sits a good amount lower in the action. For 308 family cartridges, this isn’t a huge deal and can be fixed by “tuning” the feed lips.
Unfortunately, it is a very big probably for the 223 family. Basically you’d have to either modify the magazine itself or the magazine release lever in order to get the magazine to sit higher up into the action in order to feed rounds properly. MANY folks have attempted this, and probably 95-98% of them have failed and given up on a Ruger American 223 working in a Magpul Hunter stock.
Another issue with 223 AICS magazines in a Ruger 223 is that if you want reliable feeding you basically have to have a magazine with extended feed lips. Either an Accurate Mag metal magazine that has a polymer insert in it with SPECIALLY REQUESTED(by phone or email) EXTENDED feed lips, such as that used by the “Ruger 90458” magazine(now discontinued and almost impossible to find). Ruger also makes a polymer 223 AICS magazine for the RPR that they used to make in 223/556. With this polymer magazine, it is almost a guarantee that you will have to sand material off of the outside of the magazine body to allow it to sit higher up into the action itself...the “fat” polymer body gets hung up on the action opening itself.
If you do want a Ruger American 223 to work in a new stock/chassis. I can not recommend highly enough the Indian Creek Design MoFo chassis. Using this chassis, and the “Ruger 90458” magazines I was lucky enough to find...my RAP 223 runs FLAWLESSLY in the ICD MoFo chassis and Indian Creek Design has the best customer service you’ll likely ever experience. If interested, talk to Gary with ICD. I can put you in contact via email if you’d like.
Attached is my RAP 223 in the MoFo chassis. It has a modular fore end system, and uses basically any AR15 hand grip or buttstock that can go on a buffer tube.
