I think your stems may have been faulty. Here is a video of my Hammer lock on stems, no black magic, just shitty video filmed in vertical orientation.
Thanks for the help Payton, some options to think about for sure as I certainly don't want to retire the hammer!!
Vapehunter! Thank you very much I now have no doubt that these stems were faulty! If I got them on as tight as a could and with the hammer held vertical and the stem horizontal it's about 2-10 seconds before the thing just fell off with no touching. And when opening your mouth you'd have to hold the stem as even that sight movement would dislodge it. I doubt I'll have much luck with hammer warranty wise, but I'll certainly be looking into some new/better stems!
Also, is UD 100% against overseas sales? I understand with the units as they are 110v