Subsonic ammo more accurate?

R

Radny97

New member
I have read in a few places that subsonic ammo out of handguns (namely 45acp and 38 special) is preferred by shooters needing the most precise accuracy (like bullseye shooters) because it is more accurate. The explanation was that handgun ballistics are such that you are only slightly above or slightly below the sound barrier. (Sound barrier is ~1100 fps depending on elevation and hand gun ammo is generally between 800 fps and 1500 fps.) And that bumping around the sound barrier can destabilize the bullet and reduce accuracy. It was further stated that rifle ballistics are in a different class here because they are going so much faster than the sound barrier that it's a non-issue. Thus, it was explained, to have the most reliably accurate handgun ammo one should load some of the heavier calibers at subsonic speeds (i.e. >1000 fps).
I recognize that there are probably ten other factors that will matter more to accuracy than this issue, but when you are aiming for perfection, every factor matters.
This explanation makes sense to me but I wanted to check with the gurus at TFL to get your input. Thanks!
 
Well the .22 target shooters, both pistol AND rifle use subsonic ammo. Eley is always one of the top choices although Federal challenged them a few years ago and did quite well in the Olympics if I remember correctly---the Federal was subsonic too.

When you get into the higher calibers I don't know if the subsonic/supersonic makes that much difference. Of course the subsonic would give reduced recoil and let you get back on target faster and if you're shooting a timed event that would certainly be a factor.
 
Part of what may contribute to subsonic ammo accuracy is the bullet weight and type of powder used. In 9mm in particular, subsonic ammo is usually loaded with the heavier 147 gr bullets. A heavier bullet in a given bore diameter means a longer bullet and, depending on the shape of the bullet, a longer bearing surface which often contributes to accuracy.

Subsonic ammo is also likely to be loaded with a small charge of fast burning powder like Bullseye. If metered carefully into consistent charges, a very fast powder will burn more completely and consistently regardless of factors like barrel length (this is why .38 Special Wadcutter loadings typically display very little variance in velocity between short and long barrels). With regards to accuracy, consistency between one round and the next is probably the biggest factor.
 
Radny97 said:
The explanation was that handgun ballistics are such that you are only slightly above or slightly below the sound barrier. (Sound barrier is ~1100 fps depending on elevation and hand gun ammo is generally between 800 fps and 1500 fps.) And that bumping around the sound barrier can destabilize the bullet and reduce accuracy.
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I'm not a ballistics scientist, but I think that explanation only touches on the periphery of the subject. From what I've read, the accuracy problem is most acute when a bullet leaves the muzzle at just barely supersonic speed and drops back to subsonic before hitting the target. It's the transition from supersonic to subsonic that destabilizes the bullet.

That said, I shoot standard power .45 ACP, so supersonic isn't an issue for me.
 
This is purely anecdotal,
When USPSA reduced major power factor from 175 to 165, it seemed that my reloaded 45acp ammo got noticeably more accurate.
Considering that both versions of 45acp are subsonic,
Maybe slower loads are just naturally more accurate.
Less disturbing to the bullet in flight??
 
The good old .45-70 is inherently low supersonic to transonic, at least in the heavy bullet loads favored for target shooting. The BPCR community experimented with subsonic loads a few years ago but shortly came back to the usual supersonic-transonic regime. Any gain in accuracy was small if there at all, and adding to an already high trajectory and long time of flight wiped out whatever there was.
 
First of all, standard .45acp and 38 special are nowhere near the speed of sound, even the +P stuff barely makes 1,000 fps in a .45acp where the 38 special will make about 1,200 fps with a 125 grain bullet. Sub 100 grain bullets will go alot faster, but the accuracy is bad to start with. You can make USPSA/IPSC major with a 230 gr .45acp only going 760 fps. I've loaded some hot .45acps over the years, notably 200 gr FMJs to over 1,100 fps and 230 grs to just over 575 fps to make minor floor for IDPA SSP using my G21 and didn't notice any accuracy difference inside of 40 yards, but the minor floor stuff took noticeably longer to cycle the gun. I also run a G31 .357SIG for carry and shoot USPSA Limited 9mm Major. My handloads for that gun are a 125 gr Montana Gold JHP over 7.8 grains of BE-86 at 1.140" OAL. They go right at about 1,420 fps and can run doubles on almost every stage. Speed is based on bullet weight and case volume, accuracy is most dependent on bullet design, which is why a hollow point 230 gr .45acp is inherently more accurate than a 9mm. However typical pistol distance doesn't reveal anything significant versus the rifle, where for example, 77gr (2,700 fps) bullets in an AR15 tend to be much more accurate than 55 gr (3,200 fps) bullets at 600 yards. The 77 grs are going slowing because they are heavier and have less case volume left for powder. Running a 55 go to 77 speeds will not make it more accurate.


Triple from the G31 during a classifier, 10 yards out.

image37253.jpg
 
Radny97 said:
Sound barrier is ~1100 fps depending on elevation...
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This is a common misconception. The effect of altitude on Mach number is so small that it can be disregarded in most circumstances.

Within the breathable portion of Earth's atmosphere, generally the only important variable is temperature. Here is a handy calculator. Within the range of temperature extremes generally experienced within the continental United States, the speed of sound ranges from 1,016 fps at -30°F to 1,180 fps at 120°F, so 1,100 fps is a useful average.

The misconception is most likely rooted in misapplication of speed of sound vs. altitude charts that are used for high-performance aircraft flight planning. These charts merely reflect the average temperature gradient as the aircraft climbs or descends; however, in most small-arms applications, the bullet is generally going to hit something before it climbs or descends enough to experience significant changes in air temperature. :)
Aguila Blanca said:
From what I've read, the accuracy problem is most acute when a bullet leaves the muzzle at just barely supersonic speed and drops back to subsonic before hitting the target. It's the transition from supersonic to subsonic that destabilizes the bullet.
Click to expand...
Precisely.

The definition of the speed of sound is the speed at which a pressure wave travels through a gas. In very simple terms, a subsonic object is moving slower than the pressure wave speed, so it pushes a shockwave in front of it. A supersonic object move faster than a pressure wave can move, so it compresses the air—basically pushing it aside—and thereby effectively outruns its own shockwave.

However, it gets tricky when an object travels close to the speed of sound, because the airflow is not uniform; the air travels faster over some parts of the object than others. This causes pressure waves to "attach" to areas of the object where the airflow is roughly equal to the speed of sound. (This is best illustrated by those awesome photos of fighter jets flying through their own vapor cones. :)) This causes a phenomenon called transonic wave drag, which is caused by flow separation behind the shockwave. Since real-world bullets are never perfectly concentric and never fly perfectly straight, the wave drag is slightly asymmetrical, causing the bullet to wobble slightly. HOW MUCH it wobbles depends on a bunch of other variables. :)

Mandatory disclaimer: This explanation is drastically simplified for public consumption. ;)
 
I am sure tests have been done, but I don't know of any that would definitively prove the idea either way. At least part of the situation is that lower velocity ammo produces less recoil, thus less flinching, less shock to the hand, easier recovery, etc. So, target shooters use low velocity ammo. And because low velocity ammo is used by target shooters, the makers concentrate on improving accuracy and keeping tight tolerances to attain the greatest accuracy. (Same with handloaders in CF calibers, of course.)

But for high velocity ammo, the makers assume that the buyer wants extra power and higher velocity and is willing to tolerate more recoil and less accuracy to get it, and so the emphasis is on those factors rather than on accuracy. Again the same for handloaders. Someone who loads hot for his .456 Superdooper rarely brags about tight groups - the whole goal is higher muzzle velocity.

Jim
 
Another footnote is that, for any given bullet and caliber/cartridge, the slowest load isn't necessarily the most accurate. The Speer reloading manual lists a wide range of loads for each bullet, and the data usually includes a listing for what their testing found to be the most accurate. It's rarely the slowest load (or the fastest).

Of course, their data are really only correct for their test barrel. YMMV.
 
Slow heavy projectiles are more precise than fast and light. This is very important in bullseye competition.
What is important to comment is the fact that you vill have to find the best load for each gun. I have never found a load that will work same in more than one gun.
So, for competitive bullseye shooting you will have to use all your reloaders knowledge.
 
I think I've said this before: Throw away your ballistic tables, load and shoot a variety of loads. Keep notes on what works best for you.

I usually save my targets, write the info on them, and photograph them when I get home.







Bob Wright
 
One factor that rarely gets mentioned when discussing bullet speed (sub vs. supersonic) and accuracy is the increased recoil associated with high speed handgun bullets.

As recoil increases, uniformity issues (grip position/strength, sight alignment etc.) will adversely affect group size. It's one reason that .22 lr target groups are remarkedly smaller than those of larger bore sizes. Uniformity in the shooter's technique is perhaps the single most important variable in accuracy.

At handgun velocities and ranges, sub vs. supersonic velocities play a minor role at best in accuracy.

Best regards, Rod
 
Shooting ICORE with 38 spl, 160 grain bullet and needing a power factor of 120,000 my FPS is 757-760. plenty of accuracy.
Shooting my 45 acp revolver and needing the same power factor using a 230 grain bullet my FPS is 560-580 again plenty of accuracy. I'm now using a 200 grain bullet and FPS is 640 and again plenty accurate
 
I agree with Rod in the fact that the shooters technique might be the most important variable in accuracy.
But the question was about the bullet speed and accuracy.
I believe that Rod has touched a very very good point, and thats that we shooters are the most important variable of the shooting equation.
Changing guns or ammo will not improve accuracy. Our shooting technique is the first thing that has to be improved.
 
> Mandatory disclaimer: This explanation is drastically simplified for public consumption.
---

F.W. Mann's "The Bullet's Flight from Powder to Target" is still a very good, easy-to-read reference. Copies are cheap on Amazon, or you can find downloadable pdfs since it's in the public domain now.
 
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