So you're on the right track. Pull up on the cocking knob to remove. I was feed a load of bullshit when ordering from them and they charge hefty. The metal sides on the mags could probably be ground down to allow the insertion with a closed stock, but I never bothered. The majority of reliability problems reported were because of the Zytel magazine and not the gun itself.
Gun without magazine 3.
Wipe with clean patch. The true model designations tell us a lot more about particular guns and their caliber: The guide below is designed to assist someone that is looking at different SMGs, so descriptions are more of an overview than a complete run-down. I'll add one to my next parts order, or try to find one at the KCR trade show next weekend. With open bolt guns this is not a issue because the rounds are not placed into the chamber until they are fired.