Glad you ordered the LaRue rifle, I'm sure you will be happy with it. In answer to your question, no the M1/M14 Lula will not fit the AR type magazines. You will need the M16/AR15 Lula. I have used one for a couple of years and they are well worht the money. Yeah, I can load a magazine by hand, but when it comes to unloading a magazine (without sending rounds down range) you can't beat a MagLula. Aroud our part of the country they retail for around $35.00, you can probaly find one on Amazon.com for less. Good luck and I will be watching for your range report.
Ok, I might have misunderstood your question. I made an assumption that you ordered the OBR 556. If that is correct then what I told you is correct. IF you ordered the OBR 7.62 then I really can't answer your question. I do know the other AR style 7.62 rifles use different manufacturer magazines. I hope someone that knows for sure will chime in.