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I found notes to 230gr 45 ACP at 956 fps with 6.5gr of Unique from the same 5.5” Ruger Blackhawk Bisley. I’m still looking for 10” results. It’s possible I didn’t record it.

Same load/bullet from a 5" 1911 produced 926 fps, so the average difference was an additional 30 fps for 1/2" of barrel.
 

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Biggest spread I've seen in my loads was a 6" wheel gun in 357 shooting over the chrony at 1460fps and 1995fps out of a 20" R92 Rossi. Both w Montana Gold 125 gr HP with a decent load of Aliant 300MP.
 

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Short answer is, yes. A 230gr 45 ACP hand load can break the sound barrier from a 10” barrel.
Thanks for double-checking. My preference for subsonic self-defense ammo is difficult to integrate with my interest in having an AR-style weapon, because of NJ's cosmetic "assault" weapon rules. With a full-length 16"+ rifle barrel, it would be difficult to find subsonic ammo. With a shorter barrel, in NJ you would have to follow a Mossberg Shockwave design philosophy, of keeping the overall length above 26" which is going to require some barrel length to satisfy the Shockwave style of being stockless.
 

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50 State, What's the big deal about sub-sonic self-defense ammo?
 
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Thanks for double-checking. My preference for subsonic self-defense ammo is difficult to integrate with my interest in having an AR-style weapon, because of NJ's cosmetic "assault" weapon rules. With a full-length 16"+ rifle barrel, it would be difficult to find subsonic ammo. With a shorter barrel, in NJ you would have to follow a Mossberg Shockwave design philosophy, of keeping the overall length above 26" which is going to require some barrel length to satisfy the Shockwave style of being stockless.
i have a Hi-Point 45 ACP carbine I’ve never tested for velocity.
Sky Plant Hat Air gun Shooting range


Keep in mind, I’m loading my own ammo. Standard military grade ball ammo isn’t going that fast.


50 State, What's the big deal about sub-sonic self-defense ammo?
Breaking the sound barrier indoors probably. It’s one thing to fire a supersonic bullet outside, inside, it’s exponentially louder. That’s the whole premise around the 300 blackout.
 

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How does volume increase?
Which is louder muzzle blast or sonic blast?
 
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How does volume increase?
Which is louder muzzle blast or sonic blast?
The sonic boom is a compressed version of whatever the subsonic sound is. So no matter what you are shooting, it will always be louder. The issue is that in the average size living room or bedroom, that compressed sound has nowhere’s to go but back at you. You can suffer permanent hearing damage from it.
 

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The loud sound produced when firing a gun comes from the exit pressure when the bullet leaves the muzzle and has virtually nothing to do with being supersonic or subsonic. In fact, many times a sub-sonic report will be much louder than a super-sonic report. Here's a QuickLOAD chart that plots velocity versus chamber / barrel pressure at different barrel lengths. This load uses 8.0gr of Unique, a 185gr Speer TMJ, in a 45 ACP case.

Blue line and numbers on the right for velocity, red line and numbers on the left for chamber/barrel pressure, black numbers at the bottom for barrel length.


As you can see, the bullet will exit a 5" barrel at 1090 fps, which is sub-sonic. However, there is still 4281 psi barrel pressure when the bullet exits. This will produce a very loud report, indoors or out. With an 8" barrel, the bullet exits the muzzle well above supersonic speed at 1240 fps, however the barrel pressure is just 2433 psi .... the report is not nearly as loud as a 5" barrel. With an 18" barrel, velocity is 1463 fps with an exit pressure of a mere 839 psi. This will still make a bang but the report will be way less than an 8" or 5" barrel.

Here's a more dramatic chart using a 357 Mag with a 158gr bullet and16gr of W-296:


With a 3" barrel, you will get a very very loud report from the 19,500 psi exit pressure, yet the bullet is still sub-sonic @ 1060 fps. With a 6" barrel, the bullet is exiting the muzzle far beyond supersonic speed at 1420 fps with an exit pressure of 8000 psi. This will still make a very loud report but nothing like the report from a 3" barrel.

This whole Internet sub-sonic trend is so full of misinformation that it totally defies science and common sense. Sonic boom is a product of an object passing by you traveling higher than the speed of sound, which is about 1125 fps at sea level. The loudness of the sonic boom's shockwave is directly related to the size of the object that breaks the sound barrier. A fighter jet will produce a huge shockwave and a very loud boom. A supersonic bullet fired from a gun will also generate a sonic boom but because the bullet is so small, the shock wave is also very small. If a supersonic bullet passes by you within a few yards, you will hear the shock wave but it won't be a boom, it will sound like a "crack" from a whip. A sub-sonic bullet passing close by will make a "swish" sound. If you are several yards away from a passing bullet, chances are you won't even hear the bullet's crack or swish but you will still hear the gun's report.
 

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The loud sound produced when firing a gun comes from the exit pressure when the bullet leaves the muzzle and has virtually nothing to do with being supersonic or subsonic. In fact, many times a sub-sonic report will be much louder than a super-sonic report. Here's a QuickLOAD chart that plots velocity versus chamber / barrel pressure at different barrel lengths. This load uses 8.0gr of Unique, a 185gr Speer TMJ, in a 45 ACP case.

Blue line and numbers on the right for velocity, red line and numbers on the left for chamber/barrel pressure, black numbers at the bottom for barrel length.


As you can see, the bullet will exit a 5" barrel at 1090 fps, which is sub-sonic. However, there is still 4281 psi barrel pressure when the bullet exits. This will produce a very loud report, indoors or out. With an 8" barrel, the bullet exits the muzzle well above supersonic speed at 1240 fps, however the barrel pressure is just 2433 psi .... the report is not nearly as loud as a 5" barrel. With an 18" barrel, velocity is 1463 fps with an exit pressure of a mere 839 psi. This will still make a bang but the report will be way less than an 8" or 5" barrel.

Here's a more dramatic chart using a 357 Mag with a 158gr bullet and16gr of W-296:


With a 3" barrel, you will get a very very loud report from the 19,500 psi exit pressure, yet the bullet is still sub-sonic @ 1060 fps. With a 6" barrel, the bullet is exiting the muzzle far beyond supersonic speed at 1420 fps with an exit pressure of 8000 psi. This will still make a very loud report but nothing like the report from a 3" barrel.

This whole Internet sub-sonic trend is so full of misinformation that it totally defies science and common sense. Sonic boom is a product of an object passing by you traveling higher than the speed of sound, which is about 1125 fps at sea level. The loudness of the sonic boom's shockwave is directly related to the size of the object that breaks the sound barrier. A fighter jet will produce a huge shockwave and a very loud boom. A supersonic bullet fired from a gun will also generate a sonic boom but because the bullet is so small, the shock wave is also very small. If a supersonic bullet passes by you within a few yards, you will hear the shock wave but it won't be a boom, it will sound like a "crack" from a whip. A sub-sonic bullet passing close by will make a "swish" sound. If you are several yards away from a passing bullet, chances are you won't even hear the bullet's crack or swish but you will still hear the gun's report.
Here’s some actual decibel testing.

Percussive pressure while it does impact sound is not the same as compressed sound waves. In addition, compressed sound waves are not generated at the muzzle but start compression while the bullet is still in the barrel.
 

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Thanks guys, much appreciated. My understanding is that, everything else being equal, the sonic boom roughly doubles the noise. That seems to be borne out at least by the youtube videos that alternate super/sub rounds to demonstrate the difference in sound.

NJ does not allow suppressors, so I guess an unsuppressed subsonic round will be loud enough for a tactical scenario, and I don't want to make it any louder by cracking the sound barrier.

I guess subsonic .300 black is a thing, so the challenges are: (1) to figure out how long my barrel can be, while keeping the ammo subsonic, and (2) to figure out how to adjust my gas system to cycle the sub ammo unsuppressed.

The barrel will have to rifle length (or close to it) because of NJ's cosmetic restrictions. But I guess some rifles are known to fire subsonic black, such as the M-14, so having to use a rifle-length barrel does not have to be a deal-breaker.

The manufacturers of those rifles say they'll cycle subsonic suppressed, so I'm trying to learn adjustable gas systems to cycle unsuppressed. I guess some guys say they bore out their barrels' gas ports? Because the gas port's diameter is the upper limit on the adjustable gas system's output.
 

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Thanks guys, much appreciated. My understanding is that, everything else being equal, the sonic boom roughly doubles the noise. That seems to be borne out at least by the youtube videos that alternate super/sub rounds to demonstrate the difference in sound.

NJ does not allow suppressors, so I guess an unsuppressed subsonic round will be loud enough for a tactical scenario, and I don't want to make it any louder by cracking the sound barrier.

I guess subsonic .300 black is a thing, so the challenges are: (1) to figure out how long my barrel can be, while keeping the ammo subsonic, and (2) to figure out how to adjust my gas system to cycle the sub ammo unsuppressed.

The barrel will have to rifle length (or close to it) because of NJ's cosmetic restrictions. But I guess some rifles are known to fire subsonic black, such as the M-14, so having to use a rifle-length barrel does not have to be a deal-breaker.

The manufacturers of those rifles say they'll cycle subsonic suppressed, so I'm trying to learn adjustable gas systems to cycle unsuppressed. I guess some guys say they bore out their barrels' gas ports? Because the gas port's diameter is the upper limit on the adjustable gas system's output.
I keep a 45 bedside and the wife keeps a 380. Both are subsonic. Make no mistake, firing any gun in a closed space is going to hurt the ears. You’ll likely not be able to hear much is anything throughout the entire encounter after the first shot. Not to mention the muzzle blast in the dark will probably temporarily blind you. The idea behind subsonic rounds is to limit the damage you do to yourself.
 

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The sonic boom is a compressed version of whatever the subsonic sound is. So no matter what you are shooting, it will always be louder. The issue is that in the average size living room or bedroom, that compressed sound has nowhere’s to go but back at you. You can suffer permanent hearing damage from it.
Actually I've been about 30 yards from a 40,000 pound projectile going Mach. In fact I've ridden in one going Mach. And as a aviation structural tech I had to have a bit more than a casual knowledge if it. But unfortunately I didn't get that knowledge from YouTube.
In reality sound can be absorbed quite easily by objects in you home. Explosive gases not as much. The sound does not increase in a room. What's in the room determines how that volume is reflected to you.
 
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I keep a 45 bedside and the wife keeps a 380. Both are subsonic. Make no mistake, firing any gun in a closed space is going to hurt the ears. You’ll likely not be able to hear much is anything throughout the entire encounter after the first shot. Not to mention the muzzle blast in the dark will probably temporarily blind you. The idea behind subsonic rounds is to limit the damage you do to yourself.
I've tested that theory in a room at night with a 357. The room, all wood 15 by 20 w dirt floor. Good load of 300mp powder. I was not blinded. And I pulled weak side ear protector up about an inch. I doubt it would do anything other than cause sever ear ringing for a while. Years later issues would show up.
I stood within arms length of 20,000 pound thrust jet engines in full after burner many times. The ear damage didn't show up for over a decade.
Again the blinding and bleeding ears is internet lore. I could see pressure damage maybe firing a 357 in a small car.
 

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Actually I've been about 30 yards from a 40,000 pound projectile going Mach. On fact iI've ridden in one going Mach. And as a aviation structural tech I had to have a but more than a casual knowledge if it. But unfortunately I didn't get that knowledge from YouTube.
In reality sound can be absorbed quite easily by objects in you home. Explosive gases not as much. The sound does not increase in a room. What's in the room determines how that volume is reflected to you.
I’m happy for you. I wasn’t an aviation tech but I grew up on an air strip on an air force base. I’ve experienced my share of flybys and yes, even broke sound barriers. I can also tell you that as incredibly loud as it seems, an F18 Hornet only produced about 120 decibels of noise. This isn’t YouTube knowledge, it’s physics and it doesn’t change because of what someone believes or doesn’t. Id invite you to fire off a supersonic 9mm round in a 12’x12’ room with no hearing protection, then come back and tell me how it went.
 

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So you was outside continental USA to see Mach? I've seen em do transonic at air shows but the FAA really frowns on Mach.
 

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50 State, You got some bad information. The sonic boom does not double the noise, in fact it barely increases the sound level at all. You really need to go to a range and see for yourself instead of reading disinformation on the Internet.

It's the sudden release of pressure when the bullet exits the muzzle that makes the loud sound. Pressure does indeed start in the bore as soon as the powder charge starts burning but this happens in microseconds so we don't hear anything until the bullet exits.
 
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The shock wave at mach is determined by the size and speed of the mass of the object going Mach. That wave in open atmosphere is exponentially deteriorating. And depending on the density and size of that mass the wave hits how much further it deteriorates. Fact. The wave or volume of a .355 projectile will not exceed that of 26000 lb dry weight aircraft. In fact it will have a smaller wave relative to mass and speed.
 

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So you was outside continental USA to see Mach? I've seen em do transonic at air shows but the FAA really frowns on Mach.
They do but it still happens. Pilots get in deep shit when they do too. Some idiot out here at the Springfield National Guard air base did it just a few years ago.

As for firing off a gun in a room, I’ve had to do it too and it’s not pleasant by any stretch. I’m not trying to start an argument. The question was asked and I offered the facts.

On the extreme end I have on 3 occasions, fired off a 500 magnum without ears in. It’s painful but I once did it outside 50’ away from a building. My ear instantly closed on that side and I didn’t hear jack for 4 days. The other ear was fine. Yes that was a big gun, but it was also 50’ away from a building outdoors.

I apologize for not seeing your note on the 357. I don’t know how I missed that.
 

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50 State, You got some bad information. The sonic boom does not double the noise, in fact it barely increases the sound level at all.
That is not even remotely true. The decibel levels are not measured in linear scale, instead, it by order of magnitude. It’s measured more like the Richter scale of an earth quake. An increase in 10db is 10x as loud. An increase of 20db is 100x as loud. A gunshot at 160db is 100x as loud as one at 140db.

Fact. The wave or volume of a .355 projectile will not exceed that of 26000 lb dry weight aircraft. In fact it will have a smaller wave relative to mass and speed.
The measurement of the intensity of the sound pressure level is what a decibel is. Volume is not irrelevant for that measurement.
 
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