FX Impact FX Stackable Moderator Middle Section

"How much" depends on what caliber your shooting at what speed. 
But... I found that 3 extensions (5 pieces total, as pictured in your link) worked best overall for all 3 calibers. More sections do cut the noise down more but, it just didn't seem like it was worth it to me and it increases your chances of clipping with each section added. 
Tom
 
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