Which do you believe – SMT or Berger online Ballistic Calculator?

[Alexander-M]

The speed at 1000 yards as reported by the Silver Mountain Target display (CIHPRS match of 22 Sep 2018) averaged 1533 fps for three, 20-round matches. The difference among matches was 12 fps (1526, 1536, 1538).

I went to the range the day after the match, and without cleaning the rifle (I know, I probably should have…) I shot the (nine correction - not nine, but) 11 rounds I had left over that were the same as the ones I used for the match. My MagnetoSpeed indicated an average muzzle speed of 2861 fps.

Using Berger’s online Ballistic Calculator for these rounds using 7mm 180-gn hybrid bullets, with a muzzle speed of 2860 fps, the speed at 1000 yards is calculated to be 1723 fps, or 190 fps faster than the SMT measured!

To get down to the SMT measured speed of 1533 fps, according to the Berger calculator, I would need to have a muzzle speed of 2610 fps.

One or the other appears to be off, or maybe the true speed is somewhere in the middle?
SMT = 1533
Berger Calc = 1723

Or maybe I have made an interpretation error along the way?

What do you think?

Thx!
Alex

 

[Dos XX]

Alex, I think I remember the E target guys saying that the velocity at target was not considered to be an accurate number. I can't remember where I saw that, so I may be remembering wrong.

Also, what was the wind like? Could a head or quartering wind slow the bullet down? Any other environmental conditions you can think of that may have been different?

 

[One Shot One Thrill]

Did you check the temp setting on the SMT
If not and it was off that could induce some error. I have the SMT system and shoot a similar cartridge. I believe it should of been closer to the 1723.

 

[Dos XX]

Did you check the temp setting on the SMT
If not and it was off that could induce some error. I have the SMT system and shoot a similar cartridge. I believe it should of been closer to the 1723.

Do you find the e target velocity to pretty much line up with expected velocity from a ballistic calculator? That would be a nice piece of info if it is accurate.

 

[flintcreek6412]

My SMT speeds are always slower than the Applied Ballistic app says and the dope on the app is usually pretty dead on as long as I enter the right conditions.

 

[Keith Glasscock]

Not in my experience...

 

[One Shot One Thrill]

Do you find the e target velocity to pretty much line up with expected velocity from a ballistic calculator? That would be a nice piece of info if it is accurate.

I believe each set up is a little different. Just by luck mine stay within 50 fps as long as the temp setting is correct.

 

[JohnKielly]

Only occasionally shot on a SMT, but the Applied Ballistic elevation values for my chronographed loads are consistent with their elevation strike on the target out to 1200 yards, so I suspect that their projected velocities are pretty close too.

 

[Dusty Stevens]

Im not sure if i would believe a direct reading or a computer program that couldnt possibly take in enough data points to be accurate that far?

 

[Peebles24]

The speed at 1000 yards as reported by the Silver Mountain Target display (CIHPRS match of 22 Sep 2018) averaged 1533 fps for three, 20-round matches. The difference among matches was 12 fps (1526, 1536, 1538).

I went to the range the day after the match, and without cleaning the rifle (I know, I probably should have…) I shot the nine rounds I had left over that were the same as the ones I used for the match. My MagnetoSpeed indicated an average muzzle speed of 2861 fps.

Using Berger’s online Ballistic Calculator for these rounds using 7mm 180-gn hybrid bullets, with a muzzle speed of 2860 fps, the speed at 1000 yards is calculated to be 1723 fps, or 190 fps faster than the SMT measured!

To get down to the SMT measured speed of 1533 fps, according to the Berger calculator, I would need to have a muzzle speed of 2610 fps.

One or the other appears to be off, or maybe the true speed is somewhere in the middle?
SMT = 1533
Berger Calc = 1723

Or maybe I have made an interpretation error along the way?

What do you think?

Thx!
Alex

I think the smt targets are off on speed cause my dial in according to applied ballistics was very close. I was there saturday too. We had a pretty good cross wind but not much or any toward us.

 

[FatBoy]

I agree the SMT is off.

What's your come up from a 100y zero. That, the BC + the environmental ran through JBM will give you your speed, assuming your sights track accurately.

FWIW, when I run my data my come up is correct to within .5 moa, which is as good as I can hold with a scope. The SMT target is about 50fps off what program and my come up shows I should be at. "Real world" is about 1730fps by come up. SMT shows an average of 1719fps for one match (early morning) and 1792fps for another later that day. Difference could be the fouling and increase in ambiant temps.

 

[Ned Ludd]

Alex, what BC input did you use for the for the 180 Hybrids? Factors such as Lot-to-Lot bullet BC variance, or whether you pointed the bullets and then estimated the increased BC could be contributing factors. Also, I have accidentally failed to notice with some ballistic calculators that the default BC used is G1, rather than G7. Mixing the two will definitely cause a large difference in output.

If you are confident you input all the correct values, the next question I would ask is whether your actual elevation adjustment was more consistent with the drop predicted by the Berger ballistic calculator velocity or the SMT velocity? A 200+ fps difference in predicted muzzle velocity is huge. You should easily be able to determine from the actual vs predicted elevation settings which of the two is the better 1000 yd velocity estimate.

 

[6BRinNZ]

I shoot on SMTs a lot (most weekends). I wouldn't worry about what the SMT says.
Temp is used in the acoustic formula so if the temp probe setting was out such as a faulty probe or was sitting in direct sunlight or cooler shade it will throw the calculation out.

This is your starting point.
My MagnetoSpeed indicated an average muzzle speed of 2861 fps.

 

[Alexander-M]

XX
Winds were from 8 o’clock, around 5-10 mph, I guess (I think – I was distracted and did not look at the proper flags).
I ended up shooting with 3-6/8 MOA left on the scope, but my groups were left about 1/2 MOA, so I should have been closer to 3 MOA, and held off from there.

One Shot
No idea what the temperature setting was on the SMT.
But I did check the altitude (700 ft) and temperature (75°F) on the Berger Calculator.

FatBoy & Greg
The Berger Calculator had 24.86 MOA for come up (from a 0 at 100 yd), and I ended up with 25-2/8 up. However, after looking at my targets (20-20 hindsight), my groups were high about 2/8 to 3/8 MOA, so 24-7/8 come would have been better, as the Berger calculator specified.

I did not enter the BC; I simply selected the bullet from their drop down menu, which had a BC of 0.349.

Thank you for your thoughts!

Alex

 

[Ned Ludd]

XX
Winds were from 8 o’clock, around 5-10 mph, I guess (I think – I was distracted and did not look at the proper flags).
I ended up shooting with 3-6/8 MOA left on the scope, but my groups were left about 1/2 MOA, so I should have been closer to 3 MOA, and held off from there.

One Shot
No idea what the temperature setting was on the SMT.
But I did check the altitude (700 ft) and temperature (75°F) on the Berger Calculator.

FatBoy & Greg
The Berger Calculator had 24.86 MOA for come up (from a 0 at 100 yd), and I ended up with 25-2/8 up. However, after looking at my targets (20-20 hindsight), my groups were high about 2/8 to 3/8 MOA, so 24-7/8 come would have been better, as the Berger calculator specified.

I did not enter the BC; I simply selected the bullet from their drop down menu, which had a BC of 0.349.

Thank you for your thoughts!

Alex

If your actual drop matched closely to the Berger calculator predicted values, I think you can safely conclude that your bullets didn't arrive at the target 200 fps slower than anticipated as the SMT velocity suggested. Thanks for posting this question, Alex. It's probably something not a lot of people would have ever questioned and worth thinking about.

 

[Jdne5b]

If they cant calculate a velocity within a couple hundred fps, how can they pinpoint a location?

/troll

 

[dcali]

How exactly do e targets calculate down range velocity anyhow? I get (more or less) how they back out a shot's location, but how is velocity done?

 

[dskogman]

How exactly do e targets calculate down range velocity anyhow? I get (more or less) how they back out a shot's location, but how is velocity done?

Transit time between front and back mics I would assume.

 

[dcali]

Transit time between front and back mics I would assume.

How far apart are they on the SMT?

 

[Ned Ludd]

If they cant calculate a velocity within a couple hundred fps, how can they pinpoint a location?

/troll

Come on..aren't you familiar with the Heisenberg Uncertainty Principle? You can EITHER know the speed a particle in moving...OR you can know its location. You cannot know both at the same time. So the manufacturers of e-targets may have opted to go with location and let the speed thing lapse a little bit .