6.5 PRC Ballistics - drops don’t match ballistics chart

John Spadaro

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I tried a drop test of my 6.5 PRC. I handloaded 56.1 gn. of RL26 pushing 143gn. ELD-X bullets. MV 3105 FPS at 85F Sea Level. First problem I encountered was that my 100 yard zero was 1.5 MOA low in conditions of 2700’ MSL at 40F. I re-Zeroed at 100y in the current conditions. Then without changing my scope turrets I shot at 200, 300, 400, 500, & 600 yards. Here are the measured drops.

200 - 1.75”
300 - 6.75”
400 - 14”
500 - 32.5”
600 - 59”

Of these drops only the 200y and 600y drops match the Hornady ballistic calculations. The 300, 400, & 500y drops are less than the calculated chart.

At 600y at 2700’ msl, 40F, zero wind, the calculated MOA is 9.75. So I dialed the turret to that number and shot 3 rounds. They landed about 12” above my aim point. That equates to about 2 MOA.

I wish that I had access to 600y range to test my scope turrets at each distance. Unfortunately I can now only shoot at 100y until a Montana Elk Hunt in 3 weeks.

My question is what should I do to confirm accurate drops out to 500y and get good numbers to dial into my scope? If it matters I have a VX6 HD 3-18 TMOA scope.
 

snox801

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First stop going by the hornady drops completely useless.
Use a ballistics app and add all your info I prefer applied ballistics. It’s very good but you can also use strelok for free and it’s good. Those will get you very close still you need to check those drops after to confirm but they are usually very close for me.
 

Greyfox

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In your situation, with access limited to a 100 yard range, I would double check my mounts and bedding, then put my scope a thorough 100 yard box test and tall test to at least a 10 MOA elevation. I would then test my zero/first shot accuracy on a few separate days, checking repeatability and and velocity/ES. As others have mentioned, I would use one(or two, for confirmation) of the well proven ballistic apps, loaded for your current location. Finally, if the 500 yard dope at your current location was, for example, 7.5 MOA elevation, I would confirm the scope adjustments on your 100 yard target in 100 yard interval setting on your scope. When I reached camp, I would load the environmentals and would confirm my zero. I would then make a strong effort to make a few confirmation shots out to my expected max range. IMO.
 
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John Spadaro

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First of all you should never trust any app 100% without physically confirming them.

That was exactly my intent when I did the drop testing. Besides using the Hornady 4DOF ballistics I also used my Sig Kilo 2400 BDX. The Sig gave me roughly the same MOA drop at 600y.
 

snox801

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Sorry the way I took it was you were using the hornady info from the box of ammo. My bad. Lol you would be surprised how many do that.
And yes always double check which sounds like what you are attempting.
 

Mram10us

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Did your rifle support setup change at all? Same bipod, rear bag, front rest etc?
I zero at 300. 100 yard zero and adjusting a scope for a 300 yard shot where I hunt is useless. Great advice above regarding programs get you close, dope gets you on point.
 

John Spadaro

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Did your rifle support setup change at all? Same bipod, rear bag, front rest etc?
I zero at 300. 100 yard zero and adjusting a scope for a 300 yard shot where I hunt is useless. Great advice above regarding programs get you close, dope gets you on point.


For the drop testing I used a tripod with a ball head. This is a fairly stable setup and I can get .5 to .75 MOA groups. For the 600y shots using the scope turret I went prone on a bipod and shot a 3 shot group. The group size at 600y was .75 MOA.

I wanted to use a setup that I might use while hunting.
 

fiftybmg

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...what should I do to confirm accurate drops out to 500y and get good numbers to dial into my scope?

You need to shoot and record.

All calculators are based on math, and the math is not complex enough to account for any physical firing condition. Therefore, the math is an approximation. It is a good approximation, but not perfect.

To get the actual drop at 500 yards, you need a paper target at 500 yards - shoot at it, and measure the drop off the paper.

The cardboard packaging that fridges [refrigerator], stoves and washing machines come in, make great long range targets. One side of the box is around one square yard, and colored insulation or duct tape makes a nice big cross visible at 500 yards in the scope. Fridge packaging makes for a good tall target backing when you need to check scope tracking.

[addendum]

The drop you measure on a given day will change with altitude, temperature and humidity. It's important to record the conditions, and if you take it seriously, repeat the test several times in the year. You then have at least one drop chart that reflects actual conditions on the day.
 
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X47guy

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Did your rifle support setup change at all? Same bipod, rear bag, front rest etc?
I zero at 300. 100 yard zero and adjusting a scope for a 300 yard shot where I hunt is useless. Great advice above regarding programs get you close, dope gets you on point.

Your POI shouldn’t change if you change bags, bi pods, etc etc. If it changes with bi pods then you have to much flex in your stock and it’s touching somewhere. Anything else is poor fundamentals and poor recoil management. Are you using the TMOA reticle as hold overs? If so are you on the correct magnification? When you dial, are you sure you are using the center cross hair? Is all your data entered in the solver correct?
 

Plinker147

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With your PIO changing on your zero I would look at your scope first, it sounds like it not working correctly.

And as others have said there is no replacing actually shooting the distance and confirming dopes. If you can’t do that you shouldn’t shoot further than you can practice for hunting. Hopefully you can get to a range to confirm or get to your hunt area a day early and confirm.
 

John Spadaro

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You need to shoot and record.

All calculators are based on math, and the math is not complex enough to account for any physical firing condition. Therefore, the math is an approximation. It is a good approximation, but not perfect.

To get the actual drop at 500 yards, you need a paper target at 500 yards - shoot at it, and measure the drop off the paper.

The cardboard packaging that fridges [refrigerator], stoves and washing machines come in, make great long range targets. One side of the box is around one square yard, and colored insulation or duct tape makes a nice big cross visible at 500 yards in the scope. Fridge packaging makes for a good tall target backing when you need to check scope tracking.

[addendum]

The drop you measure on a given day will change with altitude, temperature and humidity. It's important to record the conditions, and if you take it seriously, repeat the test several times in the year. You then have at least one drop chart that reflects actual conditions on the day.
 

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John Spadaro

Well-Known Member
Joined
Nov 11, 2018
Messages
58
Location
Honolulu
You need to shoot and record.

All calculators are based on math, and the math is not complex enough to account for any physical firing condition. Therefore, the math is an approximation. It is a good approximation, but not perfect.

To get the actual drop at 500 yards, you need a paper target at 500 yards - shoot at it, and measure the drop off the paper.

The cardboard packaging that fridges [refrigerator], stoves and washing machines come in, make great long range targets. One side of the box is around one square yard, and colored insulation or duct tape makes a nice big cross visible at 500 yards in the scope. Fridge packaging makes for a good tall target backing when you need to check scope tracking.

[addendum]

The drop you measure on a given day will change with altitude, temperature and humidity. It's important to record the conditions, and if you take it seriously, repeat the test several times in the year. You then have at least one drop chart that reflects actual conditions on the day.


That is pretty much exactly what I did. I took a 6’ tall piece of cardboard and place a cross near the top as my aim point. Measured the bullet holes from the cross. See the photo I posted of part of the target.
 

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