I've got a Guarder sp140 in mine and I chrono at 455 with a .20. The mag 100 rd bake lite mags feed the best. I have 6 of the beta mags, fed well in my cybergun tactical AK47, but not so much in the Cyma for some reason. Thinking about doing another build with an SBR AK105 platform. Good luck with yours, i have a few pics of mine in a thread in the gallery section.