Range Report Reverse Figuring Data Cards???

[stillbuster]

I have run several of the ballistic calculators and they are close out to 300 yds. But beyond 300 is where the gap begins to widen in reference to what the card says as to what dope I "actually" need to put on the rifle.
FGMM is hard for me to come by and I would like to at least be on paper to start.
Is there a way to figure a more "approximate" dope using the known dope of my rifle???? I am using MOA
For example:
Rem 700 5R, 168 FGMM, 2690fps @ 70 degrees temp, 350 elev,
100 yd zero Leupy Mk4 4.5-14x50, 30mm standard rings, 20 moa base, Scope height 1.65-1.75
JBM data/ Actual firing data
200 -1.9/ ACTUAL 2 MOA
300 -4.5/ ACTUAL 4 MOA
400 -7.7/ ACTUAL ??
500 -11.4/ ACTUAL ??
600 -15.7/ ACTUAL 14.5 MOA
700 -20.5/ ACTUAL ??

 

[Lindy]

Re: Reverse Figuring Data Cards???

One of the problems you may be having is with your scope.

Leupold says the scopes with M1 knobs are calibrated in MOA.

Every one I've ever checked - which is a bunch of them - have actually been calibrated in Inches Per Hundred Yards (IPHY).

That's a 5 percent error, which makes a difference at longer distances, 2 MOA at 1000 yards with a typical .308 load.

See:

Optically Checking Rifle Scopes

One way to "tune" a ballistic program to your field shooting data is to modify the B.C. and/or the muzzle velocity. But that needs to be done with every ballistic program I've seen. You'll want to use the longest distance field data you have - with a .308, I use my 1000 yard results.

If you're a serious long-distance shooter, I highly recommend Bryan Litz's book, which contains a lot of useful information about exterior ballistics and use of ballistic programs.

Applied Ballistics for Long Range Shooting

 

[MitchAlsup]

Re: Reverse Figuring Data Cards???

Whne I dial into JBM:: 350 feet elev, 1.75 scope height, 70dF, 2690 fps

JBM gives me 14.8 MoA for 600 yards the 175 SMK (Litz) bullet. This gets rid of most of your discrepance and is within the noise level of this kind of measurement/calculation.

 

[stillbuster]

Re: Reverse Figuring Data Cards???

I played with sight height some more and got it dead on or to within .2 of my known/verified data.
So I should be close or closer.

 

[desto]

Re: Reverse Figuring Data Cards???

I got close to the same results as you did, 2 moa for 200 yards,3.75 moa for 400 yards and 13 moa for 600 yards with FGMM 168 grains. I havn't worked up anything for the 175 grain bullets as yet. I am not pleased to find out that my MK4 isn't calibrated in MOA, WTF is up with that.

 

[desto]

Re: Reverse Figuring Data Cards???

I got similar results with my Mk 4 with t1 turrets. 2 moa at 200 yards, 3.75 at 400 yards, and 13 at 600 yards with FGMM 168 grain. I am not pleased to find out my scope is not calibrated in MOA, what is up with that?

 

[Rich Emmons]

Re: Reverse Figuring Data Cards???

my 8.5x25 premier loopy is verified MOA not IPHY but if yours was IPHY it would require <span style="font-weight: bold"><span style="text-decoration: underline">more</span></span> travel than MOA scope... but none the less check it.

 

[KYpatriot]

Re: Reverse Figuring Data Cards???

I setup a track test for my scope bought new this year from Scott at Liberty. Lupy Mk4 4.5-14X50. It is definitely 1/4 MOA, not IPHY. It tracked perfectly over an over along 50 MOA worth of graduations on a large target I set up for the test, and 50 MOA is more than enough to clearly see the difference. Maybe they have changed to true MOA adjustments lately if they used to be IPHY.