? do bullets stay stable when they go sub sonic

[Paul38]

Not meaning to start a fire storm here, but all my teaching's(yeah I'm old and all my teaching's might not be up to date) were once a bullet fell back to sub sonic that it would become unstable and drift. I realize that there would be some additional yardage added due to momentum but is the bullet really stable and accurate once it reaches it's sub sonic state.
Any facts on this thought would be appreciated, maybe I can learn something. But you know what they say about teaching a old dog new tricks, I'll try.

 

[bohem]

Re: ? do bullets stay stable when they go sub sonic

Some do, some don't. It depends on the atmospheric conditions as well as the design of the projectile.

I have accurately shot 208 Amax's for several hundred yards past the sound barrier in -1000' DA conditions.

140 Amax's past it for several hundred yards at -300' DA conditions

Yet the 168 SMK's that I tried to shoot to the sound barrier at 1500' DA values didn't remain stable/correctable, I shot them again at 4500' DA and they made it no trouble to 1500yd from a 308.

 

[Dogtown]

Re: ? do bullets stay stable when they go sub sonic

It's the transition from supersonic to subsonic speeds that can cause instability in the bullet. It's a bit complicated to explain, but in simple terms the state of the air around the bullet is quite different in each state and depending on many factors, the difference going from a shockwave-forming flight to one without can impart slight off-axis forces that the gyroscoping motion can't counteract. These slight wobbles can become magnified quite quickly.

That said, good quality match bullets tend to handle that transition fine, but when they enter the subsonic range they tend to lose energy even faster, so it's often not a linear drop.

 

[bohem]

Re: ? do bullets stay stable when they go sub sonic

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">That said, good quality match bullets tend to handle that transition fine, but when they enter the <span style="font-weight: bold">subsonic range</span> they tend to lose energy even faster, so it's often not a linear drop.</div></div>


Actually, this is not an accurate statement.

The Cd curve plainly shows that the drag on the projectile drops substantially as it falls below mach transition. In transonic realm the drag force on the bullet increases non-linearly from the high speed supersonic region, and then the rate of decay of velocity (and therefore the Kinetic Energy) drops off at a higher rate.

Once it is below appx Mach 0.9 though the Cd of the projectile drops dramatically (by an order of magnitude) and the bullet continues on for a long time.

This is why a 308 throwing 175 SMK's at 2600fps may only be supersonic to about 950-1000yd at sea level, but the max range of the bullet is in excess of 4x's that distance and the impact velocity at max range (4400yd or more downrange) is still fast enough to kill.

 

[Paul38]

Re: ? do bullets stay stable when they go sub sonic

Thanks guys, sounds like it's a trial and err kind of thing or is there some kind of formula to figure out which bullets work well and at what conditions.

 

[Paul38]

Re: ? do bullets stay stable when they go sub sonic

Well lets say I'm shooting one load at sea level(where I live) and I take the same load to Eastern Oregon at 3000 ft. elevation, what differences should I expect in bullet fight.
Oh BTW did I mention, thanks for all the help, Paul<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">That said, good quality match bullets tend to handle that transition fine, but when they enter the <span style="font-weight: bold">subsonic range</span> they tend to lose energy even faster, so it's often not a linear drop.</div></div>


Actually, this is not an accurate statement.

The Cd curve plainly shows that the drag on the projectile drops substantially as it falls below mach transition. In transonic realm the drag force on the bullet increases non-linearly from the high speed supersonic region, and then the rate of decay of velocity (and therefore the Kinetic Energy) drops off at a higher rate.

Once it is below appx Mach 0.9 though the Cd of the projectile drops dramatically (by an order of magnitude) and the bullet continues on for a long time.

This is why a 308 throwing 175 SMK's at 2600fps may only be supersonic to about 950-1000yd at sea level, but the max range of the bullet is in excess of 4x's that distance and the impact velocity at max range (4400yd or more downrange) is still fast enough to kill. </div></div>

 

[bohem]

Re: ? do bullets stay stable when they go sub sonic

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: PAD</div><div class="ubbcode-body"> Well lets say I'm shooting one load at sea level(where I live) and I take the same load to Eastern Oregon at 3000 ft. elevation, what differences should I expect in bullet fight.
Oh BTW did I mention, thanks for all the help, Paul<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: bohem</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">That said, good quality match bullets tend to handle that transition fine, but when they enter the <span style="font-weight: bold">subsonic range</span> they tend to lose energy even faster, so it's often not a linear drop.</div></div>


Actually, this is not an accurate statement.

The Cd curve plainly shows that the drag on the projectile drops substantially as it falls below mach transition. In transonic realm the drag force on the bullet increases non-linearly from the high speed supersonic region, and then the rate of decay of velocity (and therefore the Kinetic Energy) drops off at a higher rate.

Once it is below appx Mach 0.9 though the Cd of the projectile drops dramatically (by an order of magnitude) and the bullet continues on for a long time.

This is why a 308 throwing 175 SMK's at 2600fps may only be supersonic to about 950-1000yd at sea level, but the max range of the bullet is in excess of 4x's that distance and the impact velocity at max range (4400yd or more downrange) is still fast enough to kill. </div></div> </div></div>

Inside of about 350yd-400yd for the conditions you stated:

Nothing.

At long ranges, starting at 600+ then you'll tend to see decreased drop and mild decreases in wind drift (due to the reduced ToF involved).

The difference between winter data on my 6.5 CM at 1000yd with the 140 Amax

H4350 driving 140 Amax at 2675 +/-10fps
-1000' DA (900' ASL @ 22F)
35.5 MOA drop from 100yd zero

Same launch conditions but at 3300' DA (1600' ASL @ 85F)
31.75 MOA drop from 100yd zero




Like mentioned above I have had 1st hand experience watching the 168 SMK go from "fussy" at 1000yd targets to hitting repeatedly at 1400-1500yd simply by being selective when I used them.

 

[Paul38]

Re: ? do bullets stay stable when they go sub sonic

Thank you sir, that just comfirms my thoughts. Now I can play at home(600 to 1000 yards)and find some loads that work and they should work back east where I shoot ELR 1500 to 2000 yards.