Want a full auto UMP but can't go back in time to invent it before 1986? Or a very affordable roller delayed carbine (that also takes HKIII binary triggers). This custom Special Weapons SP-10 has your back. Steel SEF trigger housing and full auto bolt carrier ready for drop-in operation...

This is my first post here. I looked for a similar post on here, but couldn't find any, so I apologize if this has already been discussed. For all those that have a UMP build in 9mm, where do you guys find magazines for it? I have only been able to find HK factory mags, which I have 2 of. Is...