I'll agree on using an A5 length receiver extension so you're able to use standard length carbine buffers. Armalite makes it even easier, as they have a relatively inexpensive kit that includes the extension, their spring, castle nut, H3 buffer, etc. I used this on my rifle length gas 18", no buffer or spring tuning needed.
https://www.armalite.com/product/ar1...extension-kit/
Currently sold out, but it can be sourced elsewhere.
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