Stock filler

[Joeryan]

Would like to fill my hollow synthetic stock with something to dampen the noise of the shot. Any suggestions? Considered spray foam, but thought it might be too messy.

[Geoff]

Have any old cusions or pillows ?  Memory foam type material works well and is not messy. 

[oldnamvet]

Styrofoam peanut packing material if you don't want to add any weight.

[Bullit]

Dense upholstery foam, rough cut oversized, and tightly packed into the buttstock, does very well.

[ptpalpha]

There is also a spray product called "trunk paint" which can be sprayed into the stock interior.  Dampens noise and vibration quite well on the synthetics.  The last time I found it was at an auto parts store.  It seems to be kind of a spray paint with tiny pieces of rubber in it, made for coating the trunks of cars to keep wheel noise from getting into the passenger compartment.
If you decide to go with the "Great Stuff" product, make sure you get the "doors and windows" variety as it expands much less and more slowly than the original.

[Joeryan]

Great feedback... Think I got an old woobby lying around here somewhere. Lol

[OleTomCat]

I use expanding foam for windows and doors, it has a lower expansion rate than the regular stuff and if you don't over do it you won't have foam creeping out of your trigger....