Questions about subsonic rounds

[Kimio]

As I understand it, if you want to take full advantage of a sound suppressor you want to use subsonic rounds. Using traditional ammunition will still result with a very loud crack or snap as the round is fired due to it breaking the sound barrier.

As the name implies, subsonic rounds do not break the sound barrier, so I assume that means they are flying slower.

How does this affect a rifle/handguns long range accuracy if at all. I'd imagine this would cause a significant POI shift since the rounds will begin to drop sooner than their super sonic cousins.

Please correct me if I'm wrong.

[dogtown tom]

Remington "Subsonic" .22LR is the same velocity (1050fps)
vs
CCI Standard (1070fps) That 20fps will not make one bit of difference.
vs
CCI "Quiet" (710fps) which IS definitely quieter.

Slower is always quieter than fast.
Slower is often more accurate than fast.
POI is impacted by many variables (velocity, bullet weight, etc)

[jimbob86]

How does this affect a rifle/handguns long range accuracy if at all. I'd imagine this would cause a significant POI shift since the rounds will begin to drop sooner than their super sonic cousins.

ALL projectiles fall at the same rate (IIRC, it's roughly 9.8m/sec squared) .... slow ones just have more time to fall before they reach their target ......

[Kimio]

Interesting, I always thought that subsonic ammunition would not be as effective at longer distances, I was also under the impression that the faster the round, the more accurate it is.

May I ask why slower rounds tend to be more accurate than faster ones? So subsonic ammunition would not force the shooter to re-adjust his or her rifles zero in order to compensate for greater bullet drop when shooting at distant targets?

[jimbob86]

So subsonic ammunition would not force the shooter to re-adjust his or her rifles zero in order to compensate for greater bullet drop when shooting at distant targets?

The zero will not be the same.

The slower bullet will drop much more, even though it falls at the same velocity- because it has more time to fall.

[Kimio]

Ah, okay that makes sense, thank you for the reply jimbob86.

[jimbob86]

You are welcome.

As I understand it, if you want to take full advantage of a sound suppressor you want to use subsonic rounds. Using traditional ammunition will still result with a very loud crack or snap as the round is fired due to it breaking the sound barrier.

The "crack" pales in comparison to the Boom! of a centerfire rifle round.
Most of the noise of a .22lr from a rifle is that "crack".....

[Wahoo95]

Faster is better in terms of on target effectiveness and accuracy from centerfire calibers since the bullet will most likely still be supersonic when it reaches the target. Subs have their place but are not to be confused as being equal to supers in terms of effectiveness on target. Subsonic/Standard velocity Rimfire ammo is more accurate because Rimfire aren't able to maintain their velocity over long distances. When the bullet slows from supersonic to subsonic it goes through a transition which effects accuracy.

Easiest to keep in mind the speed of sound is +/- 1,100fps depending on altitude and weather. That means regardless of caliber or bullet weight the bullet must stay below the sound barrier to remain subsonic. I shoot a lot of Subs and most have s bullet flight more like a rainbow. Still capable of good accuracy as long as you know your DOPE

[carguychris]

Originally Posted by jimbob86

The slower bullet will drop much more, even though it falls at the same velocity- because it has more time to fall.

FWIW the same basic idea also applies to lateral wind drift. A slower projectile will drift more because it spends more time in the wind.

Originally Posted by Kimio

May I ask why slower rounds tend to be more accurate than faster ones?

If the projectile slows from supersonic to subsonic speed on its way to the target, accuracy will be adversely affected by turbulence at the supersonic-to-subsonic flow transition points.

Air never flows around a moving object at a uniform rate; the speed of airflow varies at different points depending on the object's shape. In the real world, bullets are never perfectly concentric and never fly perfectly straight, so the supersonic-to-subsonic flow transitions will always be asymmetrical to some degree, causing the bullet to move around in an unpredictable way.

Target shooters who use cartridges that operate close to the speed of sound- e.g. Olympic .22LR competitors- often choose subsonic loads so this is not a factor.

Also...

Subsonic rounds often use larger projectiles to maintain equal or at least comparable muzzle energy.

Under normal atmospheric conditions- i.e. conditions in which you can survive outdoors without a space suit - the speed of sound is determined almost solely by air temperature. Humidity has a minor effect; barometric pressure and altitude also have an effect, but it is so small that it can generally be disregarded. Here's a handy calculator that you can play around with:

http://www.srh.noaa.gov/epz/?n=wxcalc_speedofsound

[Derbel McDillet]

My standard load for all my .22LR rifles is CCI Subsonic (which is loaded at "standard" velocity). It has an aggressive HP cavity and delivers better terminal performance on small game than CCI MiniMag. I've found it to be more accurate than many of the other loads I've used.

[Shipwrecked]

As long as it doesn't drop through the sound barrier sonic and sub sonic are as accurate as each other, it's dropping through that speed that buggers everything up. Generally CF rounds are for longer distances and need the speed to remain super sonic until they impact the target. RF Super sonics are for a given purpose/range. Around 100 Meters and .22 subs are fine.

[44 AMP]

Around the end of the century before last, people were shooting 1,000yard target matches with black powder rifles and iron sights.

The best shooters could turn in 10-12" groups, throwing ounce weight chunks of lead in high arching trajectories. Starting out in the 1200+fps range and passing through the sonic barrier well before reaching their targets.

Apparently the transition from super to subsonic wasn't a big concern at that time, as it is not particularly remarked on in period literature.

The transition does upset the bullet a bit, but its the size & weight of the bullet affected AND where on the way to the target it drops subsonic that has the most impact.

A big heavy bullet that drops subsonic 100yards or so from the muzzle is pretty well restabilized by the time it gets a few hundred yards more downrange. A smaller, lighter bullet (where the sonic transition turbulence has a larger effect on the bullet) that goes subsonic 2/3 of the way (or closer) to a 1,000 yd target is a different matter.

[trg42wraglefragle]

I sighted my 22lr in a few days ago with high velocity ammo about an inch high at 50yards, with this zero subsonic ammo was roughly 2 inches lower at 50yards.

I shot two rabbits, and an orange today at about 40yards and just aimed bang on and ended up with two dead rabbits and an orange with a hole in it.

[Derbel McDillet]

A big heavy bullet that drops subsonic 100yards or so from the muzzle is pretty well restabilized by the time it gets a few hundred yards more downrange. A smaller, lighter bullet (where the sonic transition turbulence has a larger effect on the bullet) that goes subsonic 2/3 of the way (or closer) to a 1,000 yd target is a different matter.

The “wobble” (instability) imparted to the bullet when it transitions from supersonic to subsonic is inconsistent from shot to shot. It disturbs the flight path of each bullet differently – which decreases accuracy and increases group size.