info taken from Jackson Rifles - about the reflex moderators, JMS arms dont publish this data about the PES but will tell you if you call them.
Baffle hole diameter
Standard baffle apertures are 7.5 mm , 8,5 mm, 10,5 mm and 13.0 mm. As a rule, the bullet caliber (bullet actual diameter ) plus at least one millimetre gives the exit aperture diameter.
7.5 mm hole takes 222, 223, 22-250, 6mm, 243, etc.
8.5 mm hole takes 6.5mm 270, 7mm, 308 , 30-06 etc.
10.5 mm hole takes 9.3mm, 338 etc.
13 mm hole takes 45-70 etc.
The reinforced "magnum" model (stamped "M") for cartridges above 30-06 case capacity has 10.5 mm exit aperture as standard (other aperture sizes to special order).
The smaller the baffle hole diameter the better the sound suppression, but the difference between each of the above hole size increments is only 1 or 2 dB. In general, it is better to reduce the sound by adding more baffles than risk making the baffle holes too small.
All rifle bullets yaw a little on leaving the muzzle. The longer the bullet the more baffle hole clearance we need to accommodate this yaw without risk of a bullet grazing a baffle. If a bullet grazes a baffle, it can cause a "flyer" (a shot which flies well out of the group).
my rifles are screwcut without the spigot, so its a bit safer to have a slightly larger exit hole.
my .30 T4 is 1/2" unf, no spigot and measures 10.5mm.
i you fancy sitcking a .308 through my PES you're more than welcome to try - just let me stand in the next field!!