I have been using and selling Metal tech BB since 2006. My team and a lot of player here in QC are using MEtal tech... I have never experienced myself a BB jam or anyone from my team.
I have seen Misfeed in highly upgraded AEG over 400 FPS / Mostly Bolt Action.
Don't forget that Metal tech is one of the Bigest BB, so too tight inner barrel who are dirty may cause jam.
I have sold over maybe 300 + bag in the past, and have seen myself maybe 10-12 bb jams, in 400 + fps airsoft gun.
Almost all bb brand have some problem at one time.
Metal tech, BB bastard and airsoft elite are still my favorites.