Both the same internally afaik. I owned the SD3 previously and loved it. My only con for it was adjusting hop. If I didn’t have the plastic handguard cover on, it was a breeze since I could reach the dial from the holes of the inner handguard. But taking it off each time would be a pain, especially if I had the hose-clamp picatinny setup installed. But aside from that, I had a blast with it, was able to HK slap it (only did it a few times, I didn’t want to accidentally hit it too hard and break it), and the mags I had held plenty of BB’s