Range Report Supersonic effective range

[kumaichi]

I'm new to all of this and from what I can find, the bullet is not "effective" once it comes out of it's supersonic state. I was playing around with one of the ballistics programs and was looking at the chart it produced. How do you know when the bullet has left it's supersonic state? I attached an image of the chart I'm referring to and probably didn't enter all the data correctly.

 

[MitchAlsup]

Re: Supersonic effective range

The speed of sound is 1125 fps at sea level <bunch of other caveats>.

However, it is the realm where parts of the airflow around the bullet are supersonic and parts are subsonic that leads to buffeting, instability and departures from the intended path. This is the transonic realm, roughfy 1350 fps to 950 fps; and the one hardest to model in 6dF ballistics models.

You particular 250 gr bullet goes transonic around 1200 yards. Now, if you pushed it up towards 2900 fps, its a whole 'nother ball game, and will not go transonic for another 225 yards.

 

[kumaichi]

Re: Supersonic effective range

That has really cleared things up for me, thanks for taking the time to respond. It does make me wonder what the barrel length, projectile size and fps is used to reach the noted 1500m effective range of the .338 lapua.

 

[MinorDamage]

Re: Supersonic effective range

Go to JBMBallistics.com and use their calculator. One of the boxes at the bottom says "show sound barrier cross". Generally it is between 1125 and 1140 fps depending on many variables such as pressure, altitude, etc. Plug in your info and go. Make sure to use the Litz BC for your projectile if it is listed.

Josh

 

[MitchAlsup]

Re: Supersonic effective range

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: craig_m</div><div class="ubbcode-body">That has really cleared things up for me, thanks for taking the time to respond. It does make me wonder what the barrel length, projectile size and fps is used to reach the noted 1500m effective range of the .338 lapua. </div></div>

In order to rach the maximum range of the 338LM you should be shooting 300 gr pills at 2850 fps. These have 100 yards more range than the 250 pills at 3000 fps.

Also note: the army "allows" 1500 yards as the max effective range in mild conditions, and this drops to 1300 yards in colder environs and to 1100 yards in artic conditions.

In my opinion, the minimum barrel length that makes sense for a 338 LM is 27" and one should look at the 1:10 twist barrels to have the option of using 300 gr and heavier VLD pills.

 

[hexades1]

Re: Supersonic effective range

Just for the fun of it you can keep shooting 250 Scenars out to 2000m with 12" twist barrel. The bullet just flies through the sonic barrier without any problems. Not all bullets do this but .338 Lapua 250 Scenars do.

The 250 Scenar will bring a litte less energy to the target compared to 300 greiners but then again it will push the shooter also a little less around with recoil.

Here in Finland rebarreling a TRG-42 or other 338LM rifles is pretty common (a friend of mine will be getting his fourth barrel soon to his TRG-42). Most people opt for 12" twist barrels because they do not see any use for the 300 Scenars or Match Kings whose trajectories are as straight as 250 Scenars.

 

[Fred_C_Dobbs]

Re: Supersonic effective range

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TA</div><div class="ubbcode-body">Just for the fun of it you can keep shooting 250 Scenars out to 2000m with 12" twist barrel. The bullet just flies through the sonic barrier without any problems. Not all bullets do this but .338 Lapua 250 Scenars do.... </div></div>
Interesting point. For a long time, conventional wisdom held that a bullet couldn't pass through the transonic region and remain stable. But those British snipers in Afghanistan wouldn't be scoring <span style="text-decoration: underline">confirmed</span> hits at almost 1000 meters beyond SoS if that were universally true. Something definitely is up with that 250 Lockbase. An engineer friend speculated they might be using computer simulations/computational flow dynamics to design bullets that aren't much disturbed by passing SoS.