Rifle Scopes Mil dot tracking

[eight]

I'm new to long range shooting and mil dot in general. A friend and I were out shooting yesterday. We both have Remington 700s with a 20" barrel. Both have mil/mil scopes, different brands. We were shooting from 100 to 500 yards to get dope. Both shooting the same FGMM 168 ammo. We did not chrono any of this.

At each 100-yard interval, we went by a general "cheat sheet" based on ammo, distance, and barrel length. My friends scope was tracking almost identical to the general guidelines. For example, if it said that adjustment at 300 yards should be 1.4 mils, he was right on at 1.4. At 300 yards, I was at 1.8. Out to 500 yards, he was right at 3.4 mils, and I was at 4.2 mils. The farther out we went, the bigger the spread in our adjustments.

Is this normal? Based on the observations, my first inclination is to think that my scope is not tracking correctly. I did not perform any other tests due to time constraints. I am going to go back and try some tracking tests at 100 yards next week.

Thanks for any help.

 

[Rob01]

Re: Mil dot tracking

Definitely check the tracking. That sounds like a classic tracking problem. I have had a few scopes that did the same thing. I always check the tracking of new scopes.

Make up a chart with marks 3.6" apart and go up to atleast 10 mils. You have a single aiming point at the bottom of the scale and use it the whole time. Dial on 1 mil at a time and take a shot. You can also lock the rifle in a vice and just dial it but I like to shoot it.

Here's a couple pics of my tracking test and this is a pic of one that was doing what it sounds like yours was. Notice how the shots are getting farther and farther from where they should be as i dial up?

 

[coldboremiracle]

Re: Mil dot tracking

What brand were the two scopes involved?

 

[DernHumpus]

Re: Mil dot tracking

Do the rifles have the same zero distance and scope over bore height?

These are very large factors as well.

 

[eight]

Re: Mil dot tracking

Thank you, Rob01. I had seen a test like that somewhere before, and that's what I want to test next.

He was using a FFP NightForce 3.5x15 (not sure exact model). I have a Premier Heritage Tactical 3x15. Both scopes zeroed at 100 yards. Not sure about height over bore differences.

 

[Rob01]

Re: Mil dot tracking

They should be similar in height over bore being mounted on the same model rifles and scopes with the same objective size. Even being off .25" won't change it that much.

Run the test and let us know how it turns out.

 

[nfoley]

Re: Mil dot tracking

Also would be interesting to chrono both rifles with the FGMM if you have access to a chronograph. Just to take that out of the equation. Interested to see how this turns out for you.

 

[roggom]

Re: Mil dot tracking

Just run some box test at 100 and see how its tracking. I played with the numbers you provided, and it is as your rifle is running 200 fps slower than the other rifle. Are both rifles exactly the same model, do you both have 20 moa bases?

 

[RingingSteel]

Re: Mil dot tracking

Improper sight height alone doesn't make that much difference. 1/2" to high on my 6.5x47 will add right at .400" every 100 meters if zeroed at 100 m. At 500m it will add 2 1/8". That added to a velocity and slight zero difference could be the culprit of a significant different impact height.

I would recomend a box test in a reasonable adjustment range. 8 mils gets me to 1000 yards. Improper tracking should show up way before that.

Another thing to think about is if you are out on the ends of your adjustment range the accuracy of tracking could possibly degrade.

 

[dk-1]

Re: Mil dot tracking

What barrel and twist rates are each rifle? I dont think a different twist rate would account for a 200 fps difference, but a different twist and a different manufacturer MIGHT. For example, if one barrel is a factory Remington with a 10 twist and the other is a rock 5r 11.25 twist, you might see an extra 200 fps in the rock barrel. I suppose the chambers in each rifle might make a difference too, one could have longer free bore which would account for less pressure and equate to a slower velocity. Go chrono each rifle and see what they are really doing. The scope tracking test should be done regardless, but I would think that they should be the same, both being high quality optics.