It just sounds like you got a spring from from the "strong" end of the pile. Or it could be a weak lot of WWB and your starting loads.
If you are concerned I'd call and ask, but it should be as simple as changing out to a slightly weaker mainspring to shoot the WWB or weaker handloads.
If you are going to concealed carry this thing I'd see if your defensive round cycles fine, and if it does just be happy with it. How many rounds do you have through it now?
Machine guns are awesome until you have to carry one.