Range Report Transonic/Subsonic - Real World Affects

[Tribe]

For sake of argument... standard atmosphere... .308 175smk running 2747fps. Precision Shooters Workbench tells me I hit Transonic at 964 yds and sub-sonic at 1,046 yds. A couple of weeks ago, we were shooting out to 1080 yds at a 13" plate. The actual conditions were actually about 20* cooler and heavy pressure... safe to say I was hitting the "wall" even earlier...

Nevertheless, we were able to score reasonably consistent hits & misses, where one might expect... but occasionally, some misses just didn't 'feel' right, as POI's would seem to jump sporadically - i.e., didn't really behave like a wind shift. Frankly, I was amazed I wasn't having more trouble, as I figured I would tap-out right around 1,000 yds.

My question is, what can one expect to see as the round hits transonic vs. subsonic... and at what point, can you pretty much chuck predictability out the window? What's a good rule of thumb for determining max affective range under given conditions?

Thanks much,
C

 

[ChadTRG42]

Re: Transonic/Subsonic - Real World Affects

At 2747 fps, I'm showing you to be supersonic til 1180-1200 yards. When you get out that far, there's a lot of conditions that effect your accuracy. How accurate is the load you are using (at 200 or more yards)? Basically, rule of thumb is anything over about 1119 fps (give or take a few fps for your elevation/enviroment conditions) will maintain accurate flight. Some bullets will handle the transonic transition better than others. I've seen guys shoot accurately when the bullet should be going about 950 fps. So, I don't think there is a text book answer for predictability. At some point it will keyhole.

 

[doc76251]

Re: Transonic/Subsonic - Real World Affects

I think you have a typo, a 175 above 2700 fps will stay super sonic a ways past 1K.

Cheers,

Doc

 

[MitchAlsup]

Re: Transonic/Subsonic - Real World Affects

As the others stated, I think you typed in 2647 not 2747 into the ballistics calculator.

 

[Tribe]

Re: Transonic/Subsonic - Real World Affects

Huh.... no typo. FFS tells me Transonic at 964yds (1200fps) & Sub-Sonic at 1046yds (1115fps)...?

 

[Lowlight]

Re: Transonic/Subsonic - Real World Affects

Don't crawl into the software, its not right... you either inputted something wrong or something else is amiss.

Most say, at 1000 yards you load is running 1271fps... so it is fine. At 900 yards you are 1376fps.

 

[*Nine]

Re: Transonic/Subsonic - Real World Affects

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">Don't crawl into the software, its not right... you either inputted something wrong or something else is amiss.

Most say, at 1000 yards you load is running 1271fps... so it is fine. At 900 yards you are 1376fps. </div></div>

I'll second this. My software on my phone is within 1fps at those distances and the given projectile and MV.

 

[Tribe]

Re: Transonic/Subsonic - Real World Affects

CRAAAAP. LL, Point me another hole to crawl into, and I'll be at it...

175SMK, BC: .496, MV: 2747, Station: 29.92, Temp: 59*, Hum.: 0.

JBM: 900yds = 1,364fps, 1,000yds = 1,260fps

FFS: 900yds = 1,278fps, 1,000yds = 1,160fps

LoadBase: 900yds = 1,296fps, 1,000yds = 1,176fps

Man... every time I think I'm sneaking up on an answer, I open up a barrel full of questions.... wtf?

 

[Tribe]

Re: Transonic/Subsonic - Real World Affects

Hey Market Garden,

Check out SHWW in the members link-up section, if you ever want to get together and shoot...

C

 

[*Nine]

Re: Transonic/Subsonic - Real World Affects

Thanks! I posted a short intro over there.

 

[ranger1183]

Re: Transonic/Subsonic - Real World Affects

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Tribe</div><div class="ubbcode-body">CRAAAAP. LL, Point me another hole to crawl into, and I'll be at it...

175SMK, BC: .496, MV: 2747, Station: 29.92, Temp: 59*, Hum.: 0.

JBM: 900yds = 1,364fps, 1,000yds = 1,260fps

FFS: 900yds = 1,278fps, 1,000yds = 1,160fps

LoadBase: 900yds = 1,296fps, 1,000yds = 1,176fps

Man... every time I think I'm sneaking up on an answer, I open up a barrel full of questions.... wtf? </div></div>

I'm getting your numbers using your given values, Tribe.

Ballistics! (cheap software program): 900yds = 1298fps, 1,000yds = 1179fps

Ballistic Calculator (also cheap software program): 900yds = 1334fps, 1,000yds = 1208fps

Exbal: 900yds = 1366fps, 1,000yds = 1262fps


However,

Why a BC of .496? My data is showing a .505 BC.

0% humidity? Sure about that number?

 

[Tribe]

Re: Transonic/Subsonic - Real World Affects

Hey Ranger..

BC is .496 at those velocities.

0% just because that's what pops up when I use the boiler-plate conditions in the software.

Shot at 200, 300, 500 & 600 last week, and FFS was nuts-on with field results.
Shot at 300 Thursday... FFS .2mil high.
Shot at 600 this morning... FFS nuts on....

I don't know the reason for such a large variance in velocities between programs, but FFS usually gives me good results.

On another note, trying to nail down velocity swings due to temperature changes for Varget. It was about 20* warmer Thursday than it has been for a long time around here, and right now, I'm adjusting 2.3fps per degree temp change... maybe it needs to be greater to explain that .2mils on Thursday...?