I had the same situation with JSB pellets, 14.5 gr Superdome.
When I switched to H&N 21 gr Barracuda (an excellent pellet!!!) my groups tightened
right up. I must assume there is something with the softer lead. I had a lot of deformed
pels in the JSB tin. The Kodiaks and H&N were spot on perfect! Every one was good.
So, I believe a heavier pellet is needed for the power of the Maudie, and the harder
lead in the Beeman and H&N seems to get the job done.
That being said, these are tight fitting pels, so you may have to push some of them
all the way in the magazine. Length is not a problem. They have wide, well formed skirts.
A VERY small price to pay for the accuracy and punch these bad boys present.
Try the H&N Barracudas. They are really nice looking, well formed, and fly straight and true.