I also did the mod of adding two more baffles to my 25 Marauder. It was much quieter, but then I started getting poor groups. I looked at the inside of the end cap and there were skids made from pellets hitting it (which I never had before). Plus there were tiny lead dust particles around some of the baffles.
I tried various things including drilling out all the baffles and the end cap, and finally going back to 4 baffles, but the accuracy just does not seem as good as it was before I started this modification.
I first drilled the 22 baffles out to the same size hole as the stock 25 Marauder holes - 5/16", but then I later bored them all out another 64th of an inch.
Any ideas? Maybe I messed up something in the barrel.
Ray