Calculator results drastically different than DOPE

[ctay20]

Very strange problem here. I'm having trouble getting anywhere near correct dope off my ballistic calculator and looking for some suggestions on where to look to find what data I'm inputting wrong. Here are the details:

Gun-
Seekins SPRO3G, 18in 1/8 barrel

Scope -
Leupold Mark 6 1-6 w/ CMR-w 7.62 in Warn RAMP34 mount. Measured with calipers at 2.6085 over bore. (process used was measure the end of the scope / 2, add in distance from bottom of scope to rail, add in distance from top of rail to middle of barrel)

Ammo -
Factory loaded Federal GM223M, 69gr Sierra MK BTHP, 2830 average MV (checked via LabRadar), G1 BC of .301, zero at 100 yards

Using Strelok Pro but very similar results in Kestrel 5700 elite. Distances acquired with Sig Kilo 2000.

335 yards:
Calculator - 1.35 mrad, result way low
Actual hits on 8" plate - 1.8 mrad

427 yards:
Calculator - 2.21 mrad, result way low
Actual hits on 8" plate - 2.8 mrad

505 yards:
Calculator - 3.05 mrad, result way low
Actual hits on 8" plate - 3.6 mrad

As you can see the calculator is WAY off. I played with changing variables until I could get close to the required clicks on the calculator and found that if I drop the scope over bore to 1.75 and drop MV to 2700 my calculator matches pretty well with actual results.

What could I be putting in wrong here to be so far off? It doesn't make sense that the calculator could be so far off from real results unless I put something in incorrectly - so that is what I'm working from. Any suggestions?

Thank you,
Chris

 

[Lowlight]

1. What are the Atmospheric Conditions you are using ?

2. Did you Test your Scope to make sure it is tracking correctly ?

Are you holding the reticle or dialing ? If dialing calibration of the scope is very important.

 

[ctay20]

1) Zero weather was 64deg, 25.1 inHg / 26% Humidity. Shooting weather was similar but not exact. I did not record the shooting weather unfortunately. Could it have that much of an effect under 500 yards?

2) I haven't tested - what test should I do? I dialed until I had hits, then returned to zero and held the same mils. Did get hits when holding so I believe that the dial is correct.

Thank you for your help!
Chris

 

[lash]

In order to better the chances that someone here can help you with your issue, I advise you to provide all of the inputs that you have in your calculator. A difference of that amount almost always ends up being a misplaced/entered input.

 

[surgeon260]

Are you sure you are inputting your BC as a G1 value into the calculator? If you accidentally input it as G7, the calculator thinks your BC is higher than it is in reality.

On a related note, the Litz G1 BC for that projectile is 0.330...

 

[ctay20]

For sure - I believe this has all my inputs. Here is an example of the 505 yd calculation as well.

Thanks,
Chris

 

[ctay20]

Are you sure you are inputting your BC as a G1 value into the calculator? If you accidentally input it as G7, the calculator thinks your BC is higher than it is in reality.

On a related note, the Litz G1 BC for that projectile is 0.330...

Good call on the Litz BC - but that makes my difference more! I know I have something wrong in here, I just don't know what. If my process for measuring bore height correct?

 

[lash]

For what it's worth, I ran your inputs through my calculator too (Ballistic) and got very much the same predicted drops that yours called out. You actual drops sound wrong for that load and projectile. You may have to look at your equipment like Frank is asking about. Probably the easiest way to get an idea if your scope is tracking is to do a tall target test. Here's a quick tutorial video that explains is plainly:

https://www.google.com/url?sa=t&rct...KRQduaVLAarz3WZCTvP2hA&bvm=bv.150475504,d.d24

 

[lash]

Good call on the Litz BC - but that makes my difference more! I know I have something wrong in here, I just don't know what. If my process for measuring bore height correct?

The simplest way to measure scope to bore height it to measure from the seam at the rings down to the center of bore in one measurement. It doesn't have to be accurate to the thousandth.

 

[ctay20]

For what it's worth, I ran your inputs through my calculator too (Ballistic) and got very much the same predicted drops that yours called out. You actual drops sound wrong for that load and projectile. You may have to look at your equipment like Frank is asking about. Probably the easiest way to get an idea if your scope is tracking is to do a tall target test. Here's a quick tutorial video that explains is plainly:

https://www.google.com/url?sa=t&rct...KRQduaVLAarz3WZCTvP2hA&bvm=bv.150475504,d.d24

Thanks - I'll give that a try. I'm leaving town for a 3gun match so I'll report back when I get home if I was able to hit anything...

Thank you!
Chris

 

[dannySH]

The simplest way to measure scope to bore height it to measure from the seam at the rings down to the center of bore in one measurement. It doesn't have to be accurate to the thousandth.

Agree 100% here. Do it this way. 2.6" seems to me to be a little high for your setup but I could be wrong.

Sent from my SM-T810 using Tapatalk

 

[TheGerman]

As mentioned, check if you're using station or corrected (I think?) pressure. I'm going to guess its something with your settings that has a weird setting in there.

Other thing I've always done since I usually work on my own data cards is to run the data through JBM and compare just to see if there are some noticeable differences. Remember, the computer will get you 90% of the way as far as trajectory, you need to record and make the final fine tuning through live fire.

 

[Lowlight]

Your scope clicks are wrong they say .2 Mil and they should be .1 ... so you are getting more movement

Unless that scopes has .2 clicks and everything I saw shows it being .1

 

[Redmanss]

Double check your Sig Kilo is outputting distances in yards and not meters. With that large of a close range discrepancy between predicted and actual, it's probably not this but still worth the verification.

 

[Patty]

I believe the sig kilo also has a line of sight mode and Angle modified range mode where it accounts for shooting angle and gives you a range. If youre accounting for angle twice, both on the range finder and in the app, you will be off in your calculations. Use one but not the other.

 

[CharlieNC]

A consistent error of 0.6 mil across multiple ranges is suspicious. Someone had a very similar issue a while back, and after many unproductive ballistic calculator mods the problem went away after the scope was removed and reinstalled. Go figure.

 

[Matches Malone]

Depends on a lot, so much I didn't bother reading the other post, though im legitimately sure everyone above have a valid point. So ill add some of my .02, with some issues I've had and maybe that might be something to look at. I still and have always first broke in the barrel, then chrono a mv. Then i use a solver to "true the drop at a few distances, but i don't use that data right off the bat, i just write them down the suggested MV of the truing. Then i get some known distance gongs out to 500 and i guess the drop by walk it on, keeping a cold barrel the best i can. i write down the temp and MV and the suspected trued MV.
Then i input data into my ballistic computer and i compare my dope to what the computer has, then i try my trued mv and see if that gets closer or worst. Usually i find at 500 or beyond, very dependent on the type of cartridge you are using, the bc is what is affecting the out come of dope at those distances. G1 is the worst for it, and shooting 70 rounds at distance to customize your bc is a pain in the ass. G1 B.C. doesn't change as the bullet drags and slows down over distance, its showing a constant drag which inaccurate to physics. I'm sorry if someone already touched on this.

 

[ZenBiker990]

Something about your particular rig or shooting style is yielding a lower effective BC. Unstable bullet flight caused by a bad muzzle crown; a bad lot of bullets that are not gyroscopically stable. Bad station pressure input. Or a scope with calibration issues. Good luck I lnow this can be maddening.