I found that the OS .25LA muffler is a bolt on swap to the Stalker .51.  After that find I remembered that I had the Stalker muffler too.  I needed nose weight so I found the OS muffler 0.2 ozs. heavier than the stock Stalker muffler.  The stinger hole is 5/16 on the Stalker and .250 on the OS. I drilled two holes right in front of the OS stinger and that equals the area of the Stalker muffler. I haven't flown the combo as the paint is drying. Soon though.