MD residents can only buy non regulated long guns from a VA ffl. No ftf allowed. Mags transferred outside of MD can be any capacity. But stocks don't matter for ar15s.
The only limit on magazines is nothing over 20 rounds can be transfered in-state. You can buy all the 30 rounders you want out-of-state, and bring them back for your personal use.
Am I correct is assuming that you have a High Standard Supermatic Citation .22 or are you looking to obtain one?
I am asking brecause I had a Supermatic Citation that I bought new in 1978. I gave it to my son about 20 years ago. He has finally gotten around to using it. He has informed me that he is having feeding problems, which is not uncommon, resulting from deformation of the sides of the magazine at the top. If you have one and have witnessed these problems, please contact me so we can discuss it.