As some have suggested I think you need to size your case head down a bit. I would also suggest that you give MEC a call to get their thoughts on what you should be trying. While I am not a fan of some of the supposed "improvements" to the single stage gear my experience with their Customer Service has been all positive. They know their equipment and will usually point you in exactly the correct direction.
BTW, what I don't like in regards to "improvements" is they made things worst. I suspect that the only improvement is a lower manufacturing cost. One is the new 600/Sizemaster primer feeder with the lift off lid. It won't accept a Chedite tray while the older design will. In addition the sweep arm on one of my new style primers feeders sweeps too far past the drop hole and causes jams. Then there is that STUPID rubber insert in the charge bars. It doesn't matter what shot you load with, at some point that insert will get grooved and when that happens it traps shot pellets in that groove and makes shifting the charge bar difficult. There are times when the only way to shift the charge bar is slap it hard enough to make it sound like a 22 short has been fired. The old style was much easier to deal with, if a pellet got crossways all you have to do is back the bar up a bit and give it a light slap. Yeah, I do have spares of that STUPID rubber insert but they only last about a month and are 2 bucks a pop. The final bug with the newer gear is the plastic pre crimp setup versus the old Spindex. Really do miss the Spindex because I almost never had a mis-aligned pre crimp with the Spindex. Now with the new style I get at least 3 or 4 mis-aligned pre crimps per box loaded. BTW these mis-aligned pre crimps make for an EXTREMELY UGLY crimp. Note, I do know that slowing down on the pre crimp stroke can help this issue but I really don't want to have to count off 3 steamboats while doing the pre crimp stroke.