Dalua,
BASC's opinion is factual based on the fact that you can distinguish a firearm as defined. With regard to sound mods it is the words "Anything which is designed" which is the key wording.
Air weapon mods are not caught where designed for use on an air weapon. The fact they may be fitted onto a section 1 firearm and work very well is totally irrellevant.
The law does not distinguish beween 'air weapon' mods and other mods. Nor does it, I contend, catch in S1 'anything which is designed to diminish...'. I base that opinion quite squarely on the fact that it simply doesn't say that in the law.
The law seems clearly to distinguish between moderators that are accessories to S1 firearms and are therefore restricted under S1 and those that are not and therefore aren't. The law does not say that those 'designed for air weapons' are exempt. The law says that moderators that are accessories to S1 firearms are not exempt.
There are to my mind grave problems in hanging too much on the word 'designed' in this bit of law:
Are good-quality airgun mods not designed to cope with airguns over 12ftlb ME? It seems unlikely that the quality makers of airgun mods (Weihrauch, AirArms, Logun, and so on) would have separate products for their UK non-S1 rifles, does it not? Particularly as the 12ftlb-thing is a UK construct and their markets are international. Are all these therefore not designed for S1 firearms and so subject to S1 control at all times?
The familliar .22 PH mods were clearly designed as moderators for S1 rifles. This seems to me to be an unarguable fact, unaltered by their perfectly reasonable and lawful use on non-S1 airguns. The same is perhaps true of SAK, Soundbiter and others.
I can see your reasoning with repsect to the S5 ammunition - and that interpretation clearly seems correct: but it does not follow that because the word 'designed' has a particular degree of importance in one bit of law that it must have the same meaning or importance in other bits of unrelated law the rest of whose wording, context and subject are entirely different.

