You could also be suffering from midcap syndrome as well, as all of the midcaps that Airtac recommend are renowned for it - if you try only half filling a mag instead of filling it all the way, does it lessen the inconsistency any?
I use the M4 EPM1-S' with airtac M4 magwell adapter, and if I load them to maximum I get wildly inconsistent shots, so I load them to about 65-70% of capacity to alleviate that.