[Kos-Mos]

A silencer on a BA rifle changes everything. ALL the noise come from 2 sources:

The barrel end, where the compression of the air and in impact of the piston on the cylinder head is making noize.
You can reduce that with the use of sorbo pads (to minimize the amount of energy transfered to the cylinder, which can resonate and create noise), and with a good silencer. You "can" make one using any tube, filled with foam. The best foam to use is the fibrous type. You can buy a bunch of boot soles and cut rings in it. Closed-cell type of foam (like insulation foam) is NOT recommended because air is not able to go past the first layer of "broken" bubbles. You also want a metal tube. Keeps the size smaller (you would need a 2" ABS tube to get a decent inner air volume Vs 1.5" aluminium tube) and be sturdy enough not to resonate the noise. BOTH ENDS NEED TO BE CLOSED! If not, you basically build a super-sized madbull Noveske "firepig"

The other noise source is the cylinder resonating. The vibration of the receiver rebounds and gets amplified in the hollow stock. What ever the brand, it always resonates. You can fill the stock with minimal expansion foam. The stuff cost 5-10$ at hardware store. Just make sure you get the minimal expansion one. Double or triple will just split your stock in half. Best thing is to leave the stock assembled. If you have a VSR or other similar clone that have a glued butt stock, make sure it is on very well and duct-tape it in place before starting, the foam will try to push it out. Drill a hole under the stock, about 1/4". That will be used to fill the stock (using the little tube that comes with the foam can) and to let air escape. Fill the stock at about 3/4 and let dry. Wait about 2 days before doing the accessible part (under the barrel and receiver). When you do it, wrap the barrel and receiver loosely with saran wrap. Fill the stock at 3/4 and put the receiver on like it will be when done. There should be enough air escape for the foam. It should foam out the sides and such. The good thing about that foam is that an X-Acto blade will cut it like butter when fully dry.

You can't really screw-up if you take your time and let the foam dry properly before gaming it.