Gnomon, I just rechecked my Sauer 20ga--which is about a dead twin for your Merkel in bore diameter--with my Skeets. Also just had the chokes opened by Mark Beasland--and the constriction I get is exactly what I asked Mark to give me. So mine seems to work OK with that much overbore in a 20ga. Maybe the conclusion is that they suck because of a lack of quality control--some OK, some not??