A buddy has an internal suppressor on his 10-22.We did a side by side test with mine which was using a screw on can with identical ammo--no noticeable difference in noise reduction
I don't dispute your statement. But, there could also be a lot of variables too and why I wouldn't give a blanket statement like that with a straight face if you think all cans are going to sound about the same. Mostly with barrel length and silencer design.
For example, some companies make integrals with really short barrels so they'll keep supersonic bullets down to subsonic levels. While at first though many people thinks that is great, but it's not from a sound reduction standpoint because all of that supersonic and still burning powder is going to be puking into the silencer and still causing excess db's and won't be as efficient as another using a 20 inch long barrel with a can hanging off of the end of it will have given the powder ample time to burn out in the barrel and thus the gas be cooling down before it enters the silencer and almost always sounds better. Same reason why if you have a detachable can, if you put it on a rifle, will almost always sound better than if you put it on a pistol with a short barrel (like the p22 or the ppks or something along those lines). It boils down to how you're using it.
I have designed and made a dozen cans over the years and have seen that first hand.
I also don't doubt that your thread on can may have sounded just as good as your buddies either. I can see that happening too. But, different designs can have an altogether different outcome.
My integral has about a 12.5" barrel and the rest is a monocore baffle stack similar to the gemtech mist that is pinned and welded underneath of the silencer tube. I don't even have the barrel ported on that one because I don't want to worry about dropping the velocity of subsonics off too much since that's generally what I shoot. And subsonics also tends to be a little more accurate too and less or faster burning powder with smaller charge levels, just is where I like to be with that gun.
Again, not trying to argue or make you think I'm calling you out or anything. I don't doubt what you said at all. But your comment isn't always going to hold true either.