How drastic of a noise difference will a person have between a 24 and 20 inch barrel with a short action caliber like 6.5 creedmoor? Is it noticeable?

.............................Yeah probably to a degree. Depends on your ear plug protection or whether any will be worn at all.......

Ever fire a 23" to a 26" tubed 300 WSM? Well if so, you are welcome to come to commiefornia and fire my 16.5" barreled 300 WSM Ruger Frontier compact for comparison...BOOOOOM!.......Lol....

It will be louder from a shorter barrel. Where it becomes objectionable is subjective. The noise doesn't seem to be a problem for me until I get below 20".

I have 16" 5.556's, 18" 243 and a 20" 308.
They are loud.

But honestly, the 24" 243 isn't close to quiet.

I bought a 22 Hornet because everyone says how much quieter they
are than other centerfires.

They definitely make less noise.
But they are still really loud.

Rifles are loud, what are you worried about?

How am I just now learning this...

Idk but why the concern over noise at 20”s with something that can damage your hearing at 24”s? Both require hearing protection to prevent damage.

600 in .243 was annoying.
#1rsi in .243 worse

Felt the blast off the #1 when i shot a deer.

Bet that makes a bit of a flash too.

I've got a 30/06 ex-mil Mauser with a 16inch barrel but I have to use a slow powder to make it flash reliably. You need a flash to go with the big boom.

My Ithaca SKB double barrel shotgun with 25 inch barrels has been said to be almost too short, but not by me. I laid it next to a 22 inch barrel Kimber 7mm-08 and they are exactly the same length. Gotta get rid of the loggy shotgun I guess.

..............Actually, no real flash is noticeable during the daylight. Never have fired it during twilight or at night. But its noise does get a few looks at the range...lol

And then when I pull out the 338-378 Accumark w/brake and fire that thing using the brake.....That really scatters 'em....LOL......A scatter gun so to speak!,,,lol

It’s been a closely guarded secret.

A Glock 19 barrel is too short to fire inside a vehicle (muzzle inside) without protection, ouch

My Mossberg 464 in 30-30 wears a 16.5 inch barrel. The report is louder than with a longer barrel but not too bad.

Sherwood

Hearing loss

FWIW I've used rifles in various calibres with barrels from 16" - 30". I really notice a sharp difference down at 16 - 18", not so much in noise but in concussive blast. Even with proper ear protection it is quite obtrusive. You also get a lot of flash in low light. Frankly I don't like these short barrels (other than in pistol calibres) for these reasons.

In non-magnum chamberings once you get to 20" any extra length makes little difference to noise, save that it moves a bit further away perhaps, but you don't seem to get that blast (unless the rifle's braked).

I've carefully avoided any centerfire wíth a barrel under 20" after the Remington 600 .308 I owned about 1970 (no earplugs, of course). At the range last week, a guy showed up with a 18" Ruger .308, Scout I think. Was prepared to double up with plugs under my muffs, but the -30 e-muffs actually handled the noise pretty well. Still, I'm staying with my 20" rule, unless someday I get a can. Not sure about what happened in next-door VA with the new laws, but if cans were banned, it really reduces my incentive to get one.

My wife’s Ruger 77 compact with a161/2 barrel is really loud!

Unless cutting down for a can I usually stop at an arbitrary 21" even with the medium sized cartridges. It seems to me a recessed target crown, what I call the floor mat crown, directs the noise away from the shooter better than the flatter crowns. You could take a hack saw to the barrel and try in in one inch increments until you got what you wanted and then have a gun smith cut it properly for you. Might leave an an extra quarter inch on for him to work with.

Noise is critical or the blast but balance is the first priority for me. I like a front action screw balance point with a slightly muzzle heavy feel. This just shoots better for me.

For my ears, 20-21" is as short as I'd go on something with 308-ish case capacity and normal pressure loads. I've had seven 6.5's at 21, 22, 22.5 and 24.

My 20" barreled CZ550FS in9.3x62 is not too bad but my 18" Ruger RSI is pretty loud even in the 2 50 savage.20 inch is about as short as I care to shoot. Always use earplugs and muffs at the range though..

He just hasn't been listening....

Not what the OP is asking, but difference in bore size (on ~ same case capacity) has a effect. I REALLY notice the difference between a 22" 243 and a 21" 358 Win.....even though it's an inch shorter the 358 isn't nearly as sharp to my ears as the 243. Probably not that big of a difference but it seems like it when I'm shooting.

Tho not a huge caliber, the RAR I have in 7.62x39 only has a 16" barrel and really barks! I put a Kaw Valley linear muzzle break on it which directs the blast forward, really helped.

20" ruger #1 RSI.......was annoying. 243 win.
Much nicer my .35 rem 760.
Boom and no roar

My 20" 243 has a sharper report than similar 308's.

my weatherby 300mag sweet loud sound 26 inch barrel/the one that will really have your ear drums vibrate is my 500 side by side English double rifle
Evil laugh

Seems the faster something is, the further I want the muzzle from my head. 16” was no issue for my 357 max single shot, and a 16” AR is far nastier on the ears than a 16” 6.8...but it’s likely more about load vs velocity vs bore size. Just my deer/hog hunting theory, but if I need a <20” barrel for ‘handiness’, then I don’t need a 3kfps chambering/load for shooting 300-600yards, either....and some mid velocity combo will do fine, and isn’t obtrusive. If I do need to reach out, then more barrel isn’t gonna hurt for any handiness and makes me feel better about blast....but that’s just my anecdotal rambling.

Sweet lord jumping Jesus...

My Wichita 14" 7mm-08 is on it's 3rd barrel, and it's backuo, a custom XP-100 is on it's second...

Over 18,000 rounds...

And I can still hear.... huh? what? hello?????

I never noticed my 18.5 inch 30-06 being too loud, nor has my 16 in 308 ever been too loud (both rounds would need ear pro out of any barrel). Subjectively, the shorter barrels make no difference. Objectively? Well I don't have a dB meter, no do I know of anyone that has metered the difference.

I have a dB meter app on my phone, I'll have to try that.

My 20" 30-06 put out a nice fireball that was visible through the scope at the range.

The muzzle on pistol with a long barrel can be a good bit farther from your face than on a rifle with a short barrel. Noise is cheaper to mitigate than muzzle blast.

I've got a Glock 43 and wherever you shoot it it's loud.

Anecdotal evidence here, but I've owned a handful of 257 Weatherby's and there is a very marked difference in noise/muzzle blast between a 24 vs 26 inch barrel. The 24in barrel is curl your toes loud with ferocious muzzle blast when compared to a 26in.

This one is amazingly quiet. 29" .22LR. Not as quiet as my suppressed 10-22, but quiet, especially with sub sonic ammo..

No one specified CF...

Just looking for quiet...

DF

The difference between a rifle and BB gun is the gas pressure at bullet escapement is above 2 atmospheres in the rifle. The gas ball expands faster than the speed of sound. When the gas ball slows to the speed of sound, a sound wave propagates with amplitude 2A and trough at cavitation [0 Atmosphere]. Deer rifles might show 10,000 psi muzzle pressure in Quickload. That does not tell how big the gas ball will be at the threshold. The bore and chamber volume as well as grains of powder are part of the equation. A big gas ball will propagate waves down to 1/2 wavelength of its diameter. This is why cannons go boom with a deep sound. The distance from the gas ball to the ear may cause amplitude roll off a 1/r^2 for far field or 1/r for near field, but that is not as important as reflected sound. Some ranges are noisy.

I took EE360 acoustics from Rubens Siegelman in 1976 when he was developing ultrasound at the Univ of WA.

But professors could not answer why CB shorts were noisy with 22" barrels and BB gun Quiet with 24" barrels. The guy who figured that out for me was the late gunsmith Randy Ketchum in 1995. The guy who figured out the 1 atmosphere above ambient math for me was a recording engineer in CA [biker] in 2005. The calculation of the reflections was in the Cohen book I read as a teen ager in the 1960s
https://www.biblio.com/book/hi-fi-loudspeakers-enclosures-cohen-abraham/d/570314656

The 24" will be noticeably quieter.

now there's something I can understand lol