I'm thinking of changing slip ons from Thunderheaders that are TOO LOUD to Samson silver bullet M-150 slip ons. Does anyone know how much quieter the Samsons would be, if any. Wise decision or not? Tell me what you all think about this swap.

 

Not much. Samson is not known to be the quietest around, but they do sound cool.

 

This might be of some help... Doesn't include all brands of slip-ons but it might give you and idea
Copied from some Twin V Web Page - Based on a '06 Bagger with stock headers

Sound from softest to loudestall 10
Stock HD.................. 93 db
Husher(closed)........ 94
Supertrapp............... 94.5
Phantom.................. 95
Husher (open) ........ 95.5
Bassani ................... 98
Keker ....................... 98
Samson.................... 99
Freedom .................101
Python................... 102