Quite frankly, i think it's the phase of the moon and the astrological sign of when the gun was produced. Some mods work better with some guns, some just absolutely SUCK
I have a Brocock Bantam Sniper HR .25 that I’ve shot using a couple of moderators. The accuracy of the rifle wasn’t affected from what I recall. Now if I put a moderator on my Prod there is an obvious POI shift. I can adjust for that and it’s still accurate.