Sub sonic .22. possibly breaking sound barrier

[Mossy500]

hey, i just got my first .22 rifle, i bought 500 rds of Remmington high velocity "thunderbolts" and a 50rd box of Remmington subsonic hollow points. but when i went to shoot them, the subs sounded just slightly quieter than the thunderbolts.
i looked at the box and it claims that the subs leave the muzzel at 1050fps. i know at around 68 degrees i dry air the speed of sound is around 1125fps.

the weather here when i was shooting was 38F and 70% humidity. so im wondering, is that enough to make my subsonics(1050fps) break the sound barrier. or did i just get a messed up batch

any help would be appreciated, thank you

 

[Mossy500]

ok, well i found a speed of sound calculator online and with the conditions here it said the speed of sound should have been about 1094fps. but thats still 40fps more than the bullets should have been going.

i saw my first sub sonic ammo about 5 years ago. my brother was shooting it out of his old single shot mossberg .22. and the sound they made was comparable to the sound of my bb gun..

 

[Bill DeShivs]

"Subsonic" rimfire ammunition is the new, fad name for "standard velocity."
It's not much quieter than high velocity, unless you use a supressor.
There is quiet rimfire ammunition. Look at CCI's " Mini Caps" in short or long configuration. Aguila makes the "Colibri" round that is very quiet.
"Subsonic" does not mean "quiet."

 

[Picher]

The .22LR tends to reach maximum velocity in 15-16 of barrel. A longer barrel will actually slow the bullet instead of increase velocity, due to friction.

It may lose close to 100 fps in a 24" barrel.

 

[B.L.E.]

I have also experienced an occasional supersonic crack from Remington Sub Sonic hollowpoints with my rifle, especially in really cold and dry weather. The colder the air is, the lower the speed of sound is.

CCI standard velocity long rifle seems to be reliably sub-sonic and I seldom get a dud round.

Just because "they" get 1050 fps with that ammo don't assume your rifle will. It's not just barrel length either. A .223 bore will shoot a different velocity than a .224 bore. A bullet that is already engaged in the rifling while chambered will have a different velocity than a bullet that goes through a half inch of freebore before hitting the rifling.

 

[darkgael]

Subsonic

"Subsonic" rimfire ammunition is the new, fad name for "standard velocity."

That's not quite true. Subsonic ammo as it is sold by most companies will produce velocities in the range of 1025 to 1080 fps. Standard velocity ammo is normally about 1130 fps. HV ammo is over 1200 fps.
RWS, Federal, Aquila (and others) market both SS and SV ammo. You can absolutely tell the difference.

About changes in the sound barrier - temperature and pressure determine the barrier speed. Pressure is a function of humidity but also of altitude. What altitude were you shooting at? (shouldn't make too much difference since the ammo has that variable built in to it in a sense.) but...add all together and...

 

[Mossy500]

my elevation is at about 200ft
ok, thanks for the input. i figured id mention i have the mossberg 702 plinkster with 18" barrel. someone mentioned barrel length and diameter so i figured id put this info out too

 

[ScottRiqui]

Good post, except that the speed of sound is pretty much just a function of temperature and (to a much lesser extent) humidity.

Altitude does not affect the speed of sound. If it was 38F and 70% humidity, then the speed of sound would be the same whether he was in the Florida Everglades or Denver.

 

[ClayInTx]

Altitude does affect the speed of sound. This was what made the U2 so hard to fly. It would not stand the stress of supersonic speed and at high altitude the stalling speed was within a few knots of sound speed. Stalling speed increases as the air gets thinner. Speed of sound decreases as the air gets thinner.

This was what happened to Frank Powers. He hit a headwind and subsonic jets can’t take supersonic air, the compressor stalls and the engine flames out. All it took was a five knot gust and he hit one.

On a cold and dry winter day it was hard to get my plane to stop flying when landing. On a hot and humid summer day I had to keep knots in my pocket or I’d prang it.

The Three H rule. Hot, high, humid. Affects planes, sound, and bullets.

Edit: Correction, no jet engine can take supersonic air. That’s why supersonic planes have baffles on the intakes.

 

[thebantas@VERIZON.NE]

Maybe try some CCI CB Short, those are quiet

 

[longranger]

Speed of sound is roughly 786mph, so anything over that is super sonic,1050fps is super sonic until it reaches < 786fps. Humidity,elevation and temperature will affect ballistics,but not to the extent that it will render 1050fps to < 786 fps. at the muzzel= advertising hype not unlike most +P ammo.

 

[berettaprofessor]

Altitude does not affect the speed of sound. Differing temperatures at differing altitudes does.....i.e., it's not the air pressure, it's the temperature at your altitude.

Wiki explains it this way:

For a given ideal gas the sound speed depends only on its temperature. At a constant temperature, the ideal gas pressure has no effect on the speed of sound, because pressure and density (also proportional to pressure) have equal but opposite effects on the speed of sound, and the two contributions cancel out exactly

 

[Mossy500]

Speed of sound is roughly 786fps, so anything over that is super sonic,1050fps is super sonic until it reaches < 786fps. Humidity,elevation and temperature will affect ballistics,but not to the extent that it will render 1050fps to < 786 fps. at the muzzel= advertising hype not unlike most +P ammo.

im not sure about this.. http://en.wikipedia.org/wiki/Speed_of_sound .. i could be wrong but usually wikipedia is pretty on..

i looked on the cci website. i have a semiauto. so i can only shoot the LRs, and there was a note in the LR description saying it wont cycle semiauto

 

[ScottRiqui]

Altitude does affect the speed of sound. This was what made the U2 so hard to fly. It would not stand the stress of supersonic speed and at high altitude the stalling speed was within a few knots of sound speed. Stalling speed increases as the air gets thinner. Speed of sound decreases as the air gets thinner.

It wasn't the altitude itself that caused the speed of sound to drop, it was the fact that it was so darn cold up at altitude.

If you look at the actual derivation for the speed of sound equations, you'll find that altitude doesn't show up anywhere in the formula, because it's not needed. The only reason altitude *appears* to affect the speed of sound is that temperature changes with altitude, and it's temperature that changes the speed of sound.

 

[ranger dave]

wow

it all bepends what you are firing them out of a 4 inch pistol will be louder then a 16 inch rifle speed of sound is 1050 fts . the subsonics are made as not to make the down range crack when the go supper sonic . not to keep muzle noise down thats what a can is for

 

[darkgael]

info

Thanks for all the info about temp/pressure/altitude, etc.
Always something to learn.
Here's a formula that does incorporate altitude into the calculation. Other formulae do not - http://www.grc.nasa.gov/WWW/K-12/airplane/sound.html

I wonder, though, having read through a number of sources just now, whether they are substituting Altitude for something else since it seems that the big effect is temperature.
Pete

 

[ScottRiqui]

Yep - they're taking altitude as an input and then using the altitude to estimate the temperature (which is what the speed of sound calculation needs.)

They even give the formulas they're using to convert altitude into temperature:

http://www.grc.nasa.gov/WWW/K-12/airplane/atmos.html


If you look at that model, you'll see that temperature is pretty constant at -70F all the way from about 36,000 feet all the way up past 80,000 feet. And sure enough, if you plug in any altitude in that range into the formula you posted, the speed of sound is the same for any of them (660 MPH). Because the temperature doesn't vary, neither does the speed of sound, even though we're talking about a 45,000 foot change in altitude.

 

[Scorch]

Speed of sound is roughly 786mph, so anything over that is super sonic,1050fps is super sonic until it reaches < 786fps.

Don't confuse miles per hour with feet per second. 786 miles per hour = 1,144 feet per second ((786*5,240)/(60*60)=1,144), so anything below 1,144 fps at STP will be subsonic.

 

[mapsjanhere]

Temperature and pressure are related in the atmosphere, at least for the ideal case assumed in these equations. Which is why you can enter both an altitude or a temperature in NASA's little program and get the same speed of sound. You can deduct the speed of sound from the density which is both pressure and temperature dependent in a gas if that's easier to see.

 

[eric75]

Don't get too scientific about the speed of sound unless you get equally scientific about the speed of the bullet. You are getting your other speed number off of the box, which could be considerably different from reality.