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When a bullet goes subsonic

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When a bullet goes subsonic

Old 05-05-2010, 06:33 AM
  #1  
bigcountry
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I have learned from experience with 204Ruger, and 22-250 that bad things happen when you go subsonic. You can be nailing a target at 600 yards (1yard 1000 yard target), and totally miss at 700 yards. Even though you are dialing in your bullistic calc.

So that got me thinkin about slugs, and 44mag in particular. Both have the potential to go subsonic before hitting thier targets. I have seen at matches where I have been in a pit and heard bullets go subsonic, and key hole. They have a different sound hitting the target. Espeically when a reloader loads down a particular load.

But it doesn't seem to affect either slugs or 300gr 44mag. Usually the most you will get out of either is 100 yards where it usually goes subsonic at 125 yards.

One instance, is with a 44 I have, I load of unique with 240gr semiwadcutter, this thing shoots about 1200fps. It shoots awesome at 20 yards, but sucks at 100 yards. Another load I shoot is H110 with 240gr xtp and it shoots 5MOA at 100 yards, but so so at 20 yards. Obviously, the sonic boom is causing problems.

Another example is, friend has a tarhung slug gun. Shots 2MOA with hornady slugs at 100 yards, but outright sucks at 200 yards some times missing the target. Told him he ought to try the newer 1800fps slugs.


Anyone have any comments on this? Or experiences?

Last edited by bigcountry; 05-05-2010 at 06:36 AM.
 
Old 05-05-2010, 07:12 AM
  #2  
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Interesting stuff....is there actually an effect on an object when it goes from sonic speeds to subsonic??? I know when it breaks that barrier, it creates a sonic boom...but..does it do anything other than slow down??? Or is it possible that cerain slugs and bullets just don't fly well once they slow down?? I have no idea....just asking if there is a reverse effect when a bullet goes from sonic to sub sonic.....
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Old 05-05-2010, 07:37 AM
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bigcountry
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Originally Posted by mauser06
Interesting stuff....is there actually an effect on an object when it goes from sonic speeds to subsonic??? I know when it breaks that barrier, it creates a sonic boom...but..does it do anything other than slow down??? Or is it possible that cerain slugs and bullets just don't fly well once they slow down?? I have no idea....just asking if there is a reverse effect when a bullet goes from sonic to sub sonic.....
Well, anytime you cross the barrier, the sound waves compress into the boom up or down. If your going faster, all the sound waves are behind and if your going slower, some are behind and some are in front. Just at that magic speed, all the sound waves are in one place. If that makes sense.

And everytime you cross you, it creates pressure around the object. Hense the reason they say a F16 flying at 100ft will break out windows if it crosses it or knock a man down.

So I would imagine this destabilizes the bullet?
 
Old 05-05-2010, 08:25 AM
  #4  
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Transsonic is 'bout .75 Mach to 1.20 Mach. Below the speed of sound, some air may be pushed to Mach 1.0. Slightly above the speed of sound, some air will not make it supersonic and will keep the bullet from experiencing full supersonic effect. So in the transsonic range you will have supersonic and subsonic air. There is a boundary layer between the two with a shock wave. The boundary layer might not be able to withhold the shock wave. Bad things follow....

At least that's what I THINK.
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Old 05-05-2010, 08:51 AM
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bigcountry
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Originally Posted by Big Z
Transsonic is 'bout .75 Mach to 1.20 Mach. Below the speed of sound, some air may be pushed to Mach 1.0. Slightly above the speed of sound, some air will not make it supersonic and will keep the bullet from experiencing full supersonic effect. So in the transsonic range you will have supersonic and subsonic air. There is a boundary layer between the two with a shock wave. The boundary layer might not be able to withhold the shock wave. Bad things follow....

At least that's what I THINK.
Exactly what wiki says about aircraft. Youthink it exist for bullets to?
 
Old 05-05-2010, 11:44 AM
  #6  
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Considering transsonic problems, I would certainly believe it's applicable, though I can't claim an advanced understanding.
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Old 05-05-2010, 11:47 AM
  #7  
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By the way...I think the reason for heavy 60gr 22lr or other slow loads is to start them out at subsonic speeds so they don't go through the transsonic range.
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Old 05-05-2010, 12:17 PM
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bigcountry
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Originally Posted by Ridge Runner
high SD bullets do better at transonic flight, and SD has alot to do with long range accuracy, this is why even though some run of the mill hunting bullets do excellant at 300 yards, they suk pond scum at 600, no matter if they're supersonic or not.
RR
But do you that because its directly coorelated with BC? In other words, things like velocity variation at 300 yards, does not matter much, but at 1000 yards, matter plenty? I have seen guys get a whole ot of oval shaped groups long range. Figured it was variations in velocity.
 
Old 05-05-2010, 01:00 PM
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bigcountry
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Originally Posted by Ridge Runner
some of both probably, I have 2 big 7mm's the AM and the STW, they will if I have a good day, both shoot in the .2's, with ES's of 12 or less, at 800 yards the AM will do 4" groups, with 160 accubonds, the STW will do 14" with a 140 BT, have a great load with the 160 for the STW but haven't tested it at 800 yet.
RR
So your saying both have love velocity spreads, and both shoot exceptional at close range, but the 140gr BT opens up at 800?

Surprised, not too much different in 140gr BT and accubonds.

BC's compare in .485 to .531 and SDs compare .248 to .283

Ever use barnes?
 
Old 05-05-2010, 03:24 PM
  #10  
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Ballisticians have known for hundreds of years the need to stabilize projectiles for best trajectory, without any knowledge of a sound barrier. A .22 cal. 35 grain rimfire standard velocity is stable at its designed velocities and ranges. A .22 cal. 55 grain boat tail round from a 22.250 needs totally different velocities, rate of twists, barrel lengths, powder type for burn rates etc. to perform at its anticipated ranges and velocities. All bullets eventuallly destabilize and fall to earth, it is just a matter of how soon. The
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