I have been making moderators for 40 yrs. and the best is baffles over sound absorbing, but that's not the whole story. Sound absorbing works well in the beginning, but they get louder over time and the absorbing material will need changing. Also, there are baffles and then there are baffles, There are significant differences between different designs. My current design uses an inverted cone, which points backwards towards the breech and is centered in the moderator by the ID of the tube and the OD of the baffle. They are located in place within the tube by M3 all thread rods 3 each equidistant around the perimeter of the baffles with tubular spacers as longitudinal locators. The all thread rods are threaded into the moderator base with the female 1/2-20 threaded center hole. Each baffle is through drilled for the M3 rods and on both sides of the baffles I use a small stack of Belleville washers between the baffle and the locating tubes. These washers are necessary as compression springs when assembling the moderator.. The forward end plate is counter bored for the tube and through drilled for the M3 all thread rods, which are slightly longer by about 5 mm. I then use stainless acorn nuts to compress the whole assembly together.
This design allowed me to adjust the size of the expansion chambers within the tube by simply using different length tube spacers on the M3 rods. I found that the first chamber being the largest works best. This first expansion chamber volume actually includes shroud volume as well because the through hole of the male moderator adapter should be as large as possible. I use a bore clearance of .020" (.5 mm). for all the baffles. The inverted cone shape of the baffles helps deflect the accelerating air column behind the pellet from disturbing the pellets flight path,which improves accuracy. I have found that using tighter pellet clearances does not reduce the sound signature that I can detect. I have also made an alignment checking tool to verify the moderator alignment to the barrel. I used precision ground rod that exactly matches the barrel ID at the muzzle. Placing this rod through the moderator after mounting and into the barrel will easily validate correct moderator alignment.
I have also found that a baffle design will reduce muzzle velocity by about 4%., where a sound absorbing design seems to reduce velocity about 2%..The velocity attenuation is caused as the differential pressure difference across the pellet is reduced because the air column in FRONT of the pellet is also attenuated as well as the pressurized air column behind the pellet..
