Range Report Rough number in FPS that a bullet goes transonic

[tnichols]

I did a search on this and couldn't come up with anything, so don't bust my balls if I missed something. The question is, is there a good rule of thumb/rough number that can be used in FPS that you know the bullet is nearing or going to go transonic? I realize that temp and altitude will come into play here. Seems like in the on line training that either Lowlight or Jacob spoke of chronoing guys before letting them go out to 800-1000 as they could not insure the bullets were going to stay super sonic and were concerned about berm size/safety. Example: We shoot mostly during the winter months with temps in the 20-40 degree F range and at 850 MSL. If we know our MV (and we do) is there a number that we know the bullet will go transonic, give or take.

 

[varmint slayer]

Re: Rough number in FPS that a bullet goes transonic

Well a 0 degrees it's about 1050 FPS roughly and at 100 degrees it's about 1160 FPS. So basically for every degree of temp increase through that range, it's about 1 FPS different. Get yourself Ballistic FTE or Shooter for you phone and it tells you all that stuff.

 

[Lowlight]

Re: Rough number in FPS that a bullet goes transonic

JBM will do it also for free...

The closer you are to 1200 or above the better off you will be... under you want to stay away from was posted above.

Here is an online tool for the actual number of the Speed of Sound:

http://www.sengpielaudio.com/calculator-speedsound.htm

30 degrees is around 1085fps

 

[tnichols]

Re: Rough number in FPS that a bullet goes transonic

Thanks VS. I run Exbal and I don't believe it tells you or indicates a number at which it goes transonic.

 

[tnichols]

Re: Rough number in FPS that a bullet goes transonic

Thanks LL. That's what I was looking for.

 

[varmint slayer]

Re: Rough number in FPS that a bullet goes transonic

Yeah I forgot about JBM.com for the free side of things. Good call Frank.

 

[azimutha]

Re: Rough number in FPS that a bullet goes transonic

I usually go by 1.2X the speed of sound and just use a ballistics calculator that shows the sound barrier crossing to figure out how much that needs to be for the current conditions. (You might want to go to increments of 25 yards/meters or less to get a better idea where that is).

There are bullets like the Berger hybrids that are designed to stay stable all the way to sub-sonic velocities...Gives you one less thing to worry about.

 

[Greg Langelius *]

Re: Rough number in FPS that a bullet goes transonic

As a ballpark figure, I trust the Pejsa spreadsheets with reasonable local conditions input. I use 1300fps as the initial break velocity value, and will fudge that downward maybe even as far as 1100fps; but my confidence degrades proportionately whenever I do that.

Greg

 

[killerwaffles]

Re: Rough number in FPS that a bullet goes transonic

When a projectile in in transonic mode, the mach number of the projectile should be within 0.8-1.2 so if you have the speed of sound at 1125, then transonic should be from 900ft/s - 1350ft/s. Anything above that will be supersonic and below would be subsonic. It is all dependent of the speed of sound at a particular location. I.E. weather conditions, altitude, etc.

 

[bohem]

Re: Rough number in FPS that a bullet goes transonic

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: azimutha</div><div class="ubbcode-body">
There are bullets like the Berger hybrids that are designed to stay stable all the way to sub-sonic velocities...Gives you one less thing to worry about. </div></div>

Except that the 7mm 180 Hybrid doesn't in DA's below ~4000' ASL

 

[daybreak1199]

Re: Rough number in FPS that a bullet goes transonic

This was helpful to me. Reference from http://www.sengpielaudio.com/calculator-speedsound.htm

The speed of sound is called Mach 1
Mach is commonly used to represent an object's speed, such as an aircraft or a missile, when it is travelling at the speed of sound or at multiples of it. The speed higher than Mach 1 is called supersonic speed.

Mach number below 1 means the flow velocity is lower than the speed of sound - and the speed is subsonic.

Mach number 1 means the flow velocity is the speed of sound - and the speed around that is transonic.

Mach number above 1 means the flow velocity is higher than the speed of sound - and the speed is supersonic.

More than Mach number 5 is called hypersonic.

 

[Timo Turl]

Re: Rough number in FPS that a bullet goes transonic

Is there a uniform measure of how a bullet performs as it falls through the transonic zone ? Some perform better than others. Has anyone figured out how to measure their stability or other as they move through this change ?

 

[spawn_mm_jtf2]

Re: Rough number in FPS that a bullet goes transonic

Can't remember where I've read this TJ, but if I remember correctly, the problem most ammo encounter as they are transonic, they experience irregular behaviour. Maybe thos who shoot at those range on paper could work out a database? See if by any luck, their is any constance to be drawn for some bullet going subsonic?

Just my opinion here... what do you guys think?

 

[damoncali]

Re: Rough number in FPS that a bullet goes transonic

You can calculate the speed of sound for a given set of conditions. You're wisest to give your self a safety margin over that number (which is about 1050 fps at 0F and 1150 at 100F), as the transonic region is not a precise thing - weird stuff can happen as you approach the speed of sound.

So basically, use a good ballistics calculator to figure out the velocity at your target, and make sure its over the speed of sound by a couple hundred fps. Practically, that means keep it over 1300 or so. You might get good results down to 1150-1200, but you're beginning to cut it close. Figuring this stuff out is quite difficult, so it's best to play it safe, in my view.