Quoted:
Will the suppressor be that much less effective for 5.56 with the ID so big?
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Are you building an M110 self propelled howitzer suppressor? 9.525" is an awfully big hole........
Smart remarks aside, most of us on this board and any US-based forum are going to be using decimal inch for suppressor dimensions, so if you're using metric, you'll get less confusion by denoting the unit.
Now, for a can that will pass 9mm caliber bullets, a .375 bore is too tight. It's good for .30 cal rifle, if not a little large, but you don't want to go under .040" diametral clearance. Even if it's aligned well enough to not have baffle strikes (in theory), too tight a through bore will disrupt bullet flight. A 9mm cal can should have apertures in the .400"-.420" range.
How well it will work with 5.56mm or .30 cal rifle depends more on the other dimensions, baffle profile, baffle spacing and blast chamber than the aperture size. There's no reason a ~.4" aperture can won't suppress 5.56, .308 and other small bore supersonic rounds decently, but if the can is optimized for low pressure pistol rounds, it's not gonna work especially well with rifles. Conversely, optimized for rifle rounds, it will have more FRP and probably higher dB in general on pistols. SilencerCo tried to do the Jack of all trades thing with the Hybrid, and they're not the first. None have worked out well in general, ending up with undesirable attributes in pretty much every role, suffering in size/weight, suppression, durability, accuracy or a combination of those. You can try to strike a balance, but there are always trade offs, and the more roles you try to press it into, the less likely it is to excel in any of them. Just like you can't make a motor vehicle that will haul lumber, tackle 5+ off road trails, dominate super street class drags and hang with sports cars on curvy mountain roads, you can't build a suppressor that will do well on everything from rimfire guns to precision rifle to pistols to SBR autoloaders to big bore hunting rifles.