Subsonic, supersonic

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  • Last Post 18 July 2009
hunterspistol posted this 07 June 2009

:shock:  What is the application for subsonic, supersonic etc. as far as handgun loads go?  For that matter, what is the speed of sound and how does that apply to shooting?  I don't quite understand all the references to speed of sound but, I imagine some of my Contender loads exceed it by quite a bit.

      Even though I've seen a lot of 22lr ammo marked as subsonic, I don't get it. Where does that fit into cast bullets, aside from the distinctive crack of a rifle? I hear that sound sometimes from a little 22 hornet.

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RicinYakima posted this 07 June 2009

It has to do with the pressure waves, supersonic, falling back and touching the nose and sides of the bullet as it slows down to subsonic. All bullets yaw to some extent, and as the pressure waves touch the bullet it puts more pressure on one side than the other.

I try to make my rifle match loads stay supersonic from the muzzle all the way to the target. Fairly easy with a round nose long bullet. With pistol bullets that slow down so much faster, it can be an issue if the target is just at the area where the bullet is dropping from super to sub sonic.

HTH, Ric

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runfiverun posted this 07 June 2009

between 875 fps and 1000 fps depending on the weather,humidity etc. it matters because if you are just above it, as your boolit slows it can cause it to be buffeted around and be inaccurate.

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JetMech posted this 07 June 2009

Actually, the speed of sound on a standard day at sea level is 1116 FPS. Standard day conditions are at 59F and 29.92 inches Hg. The speed of sound will drop to 1000 FPS at about 30000ft altitude, where the air temp is about -50F and pressure is about 8.9 inch of HG.

When a bullet transitions from above Mach 1 to below Mach, there is a definite tendency to yaw, almost the same as an aircraft. But while an aircraft's nose will yaw back and forth, with a little bobbing in there (Dutch Roll), a bullet has a high rotational component to it's flight, which causes the bullet to corkscrew thru the air. I think the bullets ballistic coefficient has something to do with the amount of yaw, but not sure.

Basically, for best accuracy, you want the bullet to stay either above or below the speed of sound from muzzle to target. But best accuracy is relative. 520 gn bullets from my 45-70 start out at 1300 fps. at 100 yds, they're still above the speed of sound and hold about 1.5 MOA. Testing at 500 yds, where the bullet is way below the speed of sounds shows that the 1.5 MOA still holds, as I can produce groups (occasionally) at that range of about 81/2 - 9 inches, if I do my part. But usually, they're around 10 to 12 inches.

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hunterspistol posted this 09 June 2009

     Thanks, guys.  I even looked it up a little, interesting subject too. This is going to give me something to think about for awhile.

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JetMech posted this 10 June 2009

One other thing to consider, if you know the bullet will transition from Mach 1+ to below, the Area Rule comes into play. Basically, if there's a change in the cross-sectional area of an object travelling at Mach 1+, a shock wave will develope there. In plain english, the more grease grooves, the more shock waves attached to the bullet and more effects on the flight of the bullet as it slows below Mach. These shock waves also increase drag, which cause the bullet to loose velocity faster.

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Ed Harris posted this 10 June 2009

An advantage of subsonic loads is better accuracy, because the projectile is not subject to dynamic instability caused by transonic buffeting as velocity decays below the speed of sound.  In my .357 cowboy rifles I get much better 100-yard grouping with 190-gr. bullets which start out subsonic, at about 1030 +/-30 f.p.s. using 4.2-4.3 grs. of Bullseye, than when trying heavier loads. The subsonic loads group best until I get the bullets over about 1350 f.p.s. which is required to keep them supersonic all the way to the target.

An advantage for field and recreational use in built-up areas is lower noise, not only at the gun, but you also eliminate the sonic “crack!” of the bullet as it passes nearby objects. If you want to shoot garden varmints without disturbing the neighbors, shooting cast bullets loaded to about 900-1000 f.p.s. using a light charge of fast burning pistol powder which results in low muzzle pressure as the bullet exits when fired from a long barreled cowboy rifle is the way to go.

Subsonic loads in most handguns are of a moderate power, giving moderate noise and recoil which is good for general use.  They are more pleasant to shoot and loosen the gun less if you shoot alot, than firing hot magnum loads all the time.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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hunterspistol posted this 10 June 2009

     Thank you, Mr. Harris.

 I have neighbors too but, everything for half a block beside me is vacant. That means I have skunks, oppossum(being southern, I feel silly saying that out loud- rather say possums!) and any kind of wild animal coming in. They seem to push under the chain link or dig under.  That's useful for me, I could create less noise with a little experimentation and the chronograph.  It also gives me a more in-depth view of rifle shooting, this is something that never really entered my mind before.   This information will make a difference in the way I look at two aspects of the things I do.

     Again, Thank You Very Much

Ron

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Ed Harris posted this 10 July 2009

Off-the-shelf, factory solutions are to get a “Cowboy” rifle with 24 inch barrel chambered in either .45 Colt or 38 Special / .357 Magnum. Fire ordinary plain lead, standard pressure ammo, such as the traditional 158-gr. lead roundnose, cowboy flatnose or 148-gr. target wadcutters in the .38 Special or normal 250-gr. lead loads for the .45 Colt. These give about 900 f.p.s. from a rifle barrel, typically group about 2 inches at 50 yards, provide more energy and are easier to hit with than a handgun, but hardly sound like a gun going off...45 Colt lead 250-gr. factory loads fired in a rifle sound more like the “boink~!” of hitting the bottom of a plastic 5-gallon pail with a wooden drumstick, rather than going “pow~!” like a gun.

Firing .38 wadcutters from the cowboy rifle is similar for low noise, but the real prize for low noise is shooting .32 S&W Long wadcutters in a rifle chambered for the .32 H&R Magnum, such as the Thompson-Center carbine. Its report resembles a .22 CB or .32 Short rimfire.

For strictly small game and recreation go with a .357 or .32 H&R Magnum, but if you want a quiet subsonic load which will kill deer within 50 yards the .45 Colt in a rifle is the way to go.

73 de KE4SKY In Home Mix We Trust From the Home of Ed's Red in "Almost Heaven" West Virginia

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bruce posted this 10 July 2009

Ed,

I know this started out in handguns, but when you mentioned the .45 LC load in  a rifle as a subsonic deer killer, I got to thinking about my Marlin 45-70 lever rifle. Could you suggest a bullet/powder combo that would be subsonic? Maybe even Bullseye powered?

Bruce

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Vassal posted this 18 July 2009

Ed Harris is the Master!!!

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