Some options from the M3 stock "exhaust mod"
Straight through design. Don't think it'll work here, but just to give an idea:
http://www.m3post.com/forums/showthr...ht=exhaust+mod
Cutting open the stock cans, taking out all the packing and covering the holes to the Heimholtz chambers.
http://www.m3post.com/forums/showthr...ht=exhaust+mod
There's a better thread by the first guy who did it, but I can't seem to find it, but this gives you an idea of what can be done, and it's pretty cheap- around $200 for the M3.
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