Ballistic calculator

[7mmRHB]

Eric, it is possible that you're using MOA on the ballistic calculator, when your scope is moving in IPHY !! You didn't say what scope you are using but if it's a Leupold it will be moving in inches as do many others. Obviously it would take more clicks to get dialed in and would account for the discrepancy you're seeing.

No need to shoot to test the scope, just put a grid on some cardboard measured in inches with numbers big enough to see at 100 yds, starting with the Zero at the top and numbered down to 33 or so inches. Anchor your gun in a shooting rest ( tape or weight it down ), put the grid at exactly 100 yards and line up your crosshair on the zero. Carefully dial up the scope and see how far it actually moves in one and two revolutions of the turret and see if it returns to zero each time. Make sure you get the paralax adjusted out before you start.

You'll know in a few seconds if your scope is IPHY or true MOA!!

Goodgrouper and I do this on each clients gun before load testing. You would be shocked at the number of clunkers that show up on this simple test !!! ----- RHB

 

[eric2381]

The scope is a Leupold LPS. 3.5-14x52.


I'll have to try out the test mentioned. It's raining today, so I am stuck inside.




I am having trouble getting my head around it, because- Do I trust the advertised BC? Or do I trust the chronograph?

The help is greatly appreciated.

 

[Pdvdh]

I am having trouble getting my head around it, because- Do I trust the advertised BC? Or do I trust the chronograph?

The help is greatly appreciated.

I've built a dual chronograph setup, and since using it, would never go back and rely on a single chronograph for establishing MVs. I use one Oehler 33 and one PACT, with skyscreens set up on a single rail at 4.5' and 5' skyscreen spacing. This allows me to confirm I'm getting good data. There have been quite a few instances where I have ID'd bad data from one chrono of the other. If the difference in measured velocity is unusually high or low between the two, I know I've thrown a bogus number on one or the other.

With all the time and effort that goes into establishing a reliable drop chart, the last thing I want to do is start the process with bogus MVs.

 

[eric2381]

Even though it says Minutes on the dial, Leupolds are really in inches per one hundred yards? How does one go abouts making a drop chart for that?

 

[royinidaho]

Is it common to find that the advertised BC to not be tue???

I'm discovering that Nosler BT advertised BCs are quite high.

However, different barrels will result in different BCs.

 

[eric2381]

It quit raining here for a bit. I'm gonna get away from the wife and kids and go and double check my velocity and check my scope while I'm there.

 

[royinidaho]

7mmrhb is giving good advice.

I standarized every thing to IPHY for my calculations. It do make a difference.

IPHY is the easiest for me to keep straight in my ol' knoggin.

It is really important that 1 IPHY actually changes 1" @ 100.

 

[eric2381]

If my scope is calibrated in IPHY, I'd like to use IPHY. I have no desire to be switching back and forth.


I got back from the range. I shot 5 shells with my load and 180gr AB. Avg. velocity was 3046 fps. I shot 5 rounds with my load and 180gr. BT. Avg velocity was 3071 fps.

Both bullets group well from my Sako 85, 300 Win mag.



I tried checking my scope the way 7mmRHB described, but I don't have a gun vice. I had my front supported with my bipod and the rear supported with my rear bag. I just couldn't keep it steady enough. I could line up the crosshairs on the zero line I drew on the paper, then twist the elevation knob a full turn (12MOA or 12 inches, I'm not sure) then turn it back to where I started. It seemed to come right back where it started on the zero mark.


Does anybody know much about the Leupold LPS and how they are calibrated?

Thanks again, Eric

 

[Pdvdh]

Even if you learn how Leupold designed and specified the turret calibration on your LPS, you still need too field proof them as 7mmRHB described, because there is no guarantee that the turrets will perform as intended by design.

7mmRHB emphasized that he and goodgrouper commonly ID'd scope turrets that did not adjust to the factory specifications. If you don't run this test, you'll just be adding further uncertainty to your troubleshooting process.

It all takes time, but you can do it right once, or possibly be doing it wrong multiple times and never get to the bottom of it.

 

[yobuck]

ill tell you what has worked for us old fools here in pa. for decades.
have a guy sitting behind you with very good tripod mounted binnoculars.
he will say something like you went right over his back. take 5 off and shoot again right now.
no computers, no weather stations, just a rangefinder, a click chart, and a spotter.

 

[Pdvdh]

Does anybody know much about the Leupold LPS and how they are calibrated?

Thanks again, Eric

I found a 2006 Leupold catalog using Google and it states 1/4 moa clicks for the LPS. Here's the link:
http://www.scribd.com/doc/2561824/-Leupold-Optics-Catalog

Provided your scope is manufactured and behaving exactly to this design specification, one click of your elevation adjustment should move your POI 0.262" at 100 yds.

How to know for sure? As 7mmRHB described. It's not terribly difficult, but as you found out, it does require a means of holding the rifle stationary while you crank the turret up and down and measure the movement on the 100 yd target. Make sure you know the exact range to your 100 yd target. I ranged mine with my Swaro LRF and found out it was actually 104 yds. That works too. Just requires a slight modification to the mathematical solution for inches/click/100yds. After I ran through this field-proofing procedure the first time, it wasn't long before I'd performed the process on each of my long-range use scopes.

Good luck.

 

[Eaglet]

Eric2381,

Try this table for the 3050 ft/sec at other ranges and see how it
works for you.

 

[7mmRHB]

Eric, We have set up three guns in the past that had an LPS 3.5 -14 scopes and they all three moved in inches and not true MOA. Sounds like your problem is in the ballistic program which should be set to IPHY ( Inches per hundred yards )!!! This is the kind of problem that is easily fixed compared to the other issues you're worried about.

Leupold marks the turret in 1/4 min. per click but is meaning ( Shooters MOA )which is 1/4 inch per click. Many other scope manufactors have done the same. It's no big deal, just use the correct setting on the Ballistic program and you will be dailing to the right numbers to hit whatever your shooting at !!! ----- RHB

 

[Boss Hoss]

This one can get tricky fast---first make sure the chronograph is accurate which can be a challenge by itself, make sure your distance to the first screen is perfect and that your calculations take that into account.

Temps, elevation and humidity play a part in this as well but the bottom line is that you can check the ranges for actual drop I have done 100 300 and 800 and with those data points verified my BC. You can go in and adjust the values in the formulas provided by the bullet makers but you need to make sure that all of your other conditions are PERFECT.