Whats typically louder, 45 acp suppressed out of a PCC or 300 blackout suppressed (subsonic)?

I have a 300 BO 8" barrel AR that is suppressed with a Daniel Defense Wave, I also have an FN-FNX in 45 ACP that is suppressed with a Dead Air Ghost-M.  And I also have a Ruger bolt action in 300 BO that the DD Wave also goes on.  I don't have a sound meter, but when shooting them this is what I feel like is the order from loudest to quietest-300 BO AR, 45 ACP pistol, and 300 BO bolt action.

I also have a 22 lr bolt action that I put the DD Wave on and when I use subsonic loads it is literally queter than a Red Rider BB gun.

45 in a 1911 is my quietest of the 2. The aR will never be less loud than sending the bcg forward on its own. Which isn’t super quiet.

The 1911 hammer keeps it locked up just a bit longer than a striker fired, so more gas goes through the can than out the ejection port.

If you eliminated the action noises and shot both through a bolt gun I bet it would be close enough you couldn’t tell them apart

I think it will depend on the setup.  I don't have any experience with a PCC in .45 ACP, but I have fired an FNX 45 using 230 gr fmj with both a Ghost M and Obidian 45.  I've also shot subsonic 220 gr 300 BLK out of a Rattler with an SRD762TI suppressor which I thought was quieter.  That suppressor is roughly 9" with a 1.75" diameter.  I should comment however that I thought all of them were quiet.

The smaller the bore generally the more quiet, but factor in action noise or the lack thereof for different results....

Example, a 300 bo sub semi auto AR would be louder than a 45acp single shot

Or a 45 acp pistol louder than a 300bo sub bolt gun...

This is hard to answer.  And probably isn't a singular answer to it.

Larger bullets do have more flight noise.

And, at the same time, I have some really quiet loads in both 45 and 300 blk.

Commercial blackout ammunition does not impress me.  And that's with a 12" integrally suppressed barrel.

I also have two integrally suppressed 45's.  One in semi and one bolt action.  Between the two, they are both very near as quiet as the other and are both quiet.  But they also have larger inside diameter and suppressor length.

I have a SBR’d 45 pcc....and a 300 of course.  The 300 is quieter.  Not by a mile, but its measurable at your ear.  The 45 is still fun.

The 45 has more available bullets/ammunition that performs properly at subsonic velocities.

Not disputing that, but the bore size is the issue.

Almost 1/2" bore is an issue.

But not just that, the relatively low pressure doesn't help any either.  A lot of the gas just blows straight through the large bore and doesn't expand out as much, or perhaps the more appropriate term would be "as quickly" as a much higher pressure round.

Turbulence and disruption works better under higher pressures.  Which the 45acp doesn't have as much of.

It's not just about having a subsonic round.  That's only part of it.  That's why many older 45 cans have to be ran wet, or have to be 12" long and 2" diameter to get decent suppression from it.

Shot a suppressed 45 acp banshee the other day and anecdotally it was louder than suppressed 300 blackout factory subsonic out of same can.  It actually made my right ear ring just a bit where the 300 blackout with subs did not.

With manual action guns and appropriate cans, .300 blk subs are gonna be quieter.

With semi autos, though, there are a lot of moving parts in both the literal and figurative sense.   Short recoil or delayed blowback tends to have less port noise than gas operated, and definitely less than simple blowback, but again, lots of variables in play.

My Marlin camp 45 is my only .45 ACP carbine, and the port noise is horrible with simple blowback and a light bolt.  But I also don't find .300 blk particularly tolerable from an AR, even with gas adjusted.  .45 pistols, again, host matters.  My 1911s and 3rd gen S&W autos I can do with no ear pro just fine running my Phoenix M, but striker fired hosts tend to snap my ears.  Same deal with 9mm, my S&W 3906 & 5906 and Beretta 92 being perfectly comfortable,  Remington RP9 a little loud for my liking, and the blowback Stribog teetering on the very edge of what I can tolerate, all with the same can model and 147 or 158 gr subs.  .380 out of my locked breech DB380 is pleasant, but very offensive from the blowback CZ83

Quietest vs terminal performance is the tradeoff

.45 is louder than .300 blk.  9mm is quieter than both.  Im not impressed with .45 suppressed.

There are always better bullets that can do better terminal performance when doing only subs. Like the 458 socom has terminal performance that makes the 45 look like a BB gun. It is the fact that the 300BLK can with a magazine change can go from a quiet subsonic platform that has the same if not better terminal performance with the proper ammo as the 45 to the terminal performance of a rifle caliber.

Good terminal performance .300 Blackout subs will always be much more expensive than the .45 but can carry that terminal performance out to 200-300 yards where a .45 slug will have started slowing down at 100 yards.  Whether that’s a practical application is another matter.

I had a bolt action .45acp and have a 77/44, both 16" barrel length, shooting subs through a Cosmic. The .45acp was noticeably quieter at the ear. I've been trying to figure that one out for a while. Could be powder used, i guess.