I've been experimenting to optimize a design for 30 fpe + short barrel .bullpup.
Sometimes I just want the rifle as compact as possible, if I can get it acceptably quiete.
Tested in the P12 at 31 fpe... Barrel length 42 cm.
All the inserts are the same 12 cm in length.
I'll select the best design and test shorter lengths later.
Tested indoors dry fired... Shooting a pellet reduces noise by about 1 dB... Doesn't make a huge difference.
Rifle without factory cone end cap... 105 dB.
With end cap 97. 5dB.
First started with my normal design... Perforated with cone baffles wrapped with polyester batting.
Unit just threads into the shroud.
Shroud moved forward for 5 mm gap between insert and factory air stripper treaded to the barrel.
94 dB..... Moved shroud forward 8 cm gap 89db. This design works best for lengths of about 20 cm.
New design with 12 vent holes surrounding the centre hole.
Air starts venting through the small holes first reducing back pressure and major air blast.
5mm gap 91 dB.... 8 cm gap 89.5 dB.
This design is very effective with a small gap, it gains very little when the shroud is extended.
Painted black too see what it looks like installed.
Different designs I've tested up to now.
The white one with the large holes near the top baffle is the best performing.
My large 20 cm 38mm diameter silencer.. 85 dB.
Gamo cf 30... 95.7 dB
Dropping a coke bottle cap from waist height.. 83 dB.
I'm very impressed how well 1mm pitch thread printed.