6.5 PRC Ballistics - drops don’t match ballistics chart

[John Spadaro]

Last question - how much vertical do your groups at 100 yards have? Normally when I do a tall target I put a couple shots at each distance. much easier to true apps if you put a couple shots at each distance and don't have much vertical in your groups.

At 100y I normally get my group to less than 1/2". I wish I had done groups of 3 at each distance but I was pressed for time.

 

[John Spadaro]

You another pilot?

Yes, how did you know?

 

[Mram10us]

it changes because you have poor fundamentals. POI should not change moving from prone, standing, kneeling, off a bench, off a tripod, off a bi pod etc. If you change a bi pod then you can create a different flex on the stock. In a properly bedded stock, it will not change.

I knew I'd run into one.... you are ignorant to my fundamentals. Have you seen me shoot? Keep your ignorant comments to yourself.

 

[John Spadaro]

What was your air pressure at 2700'?

Running isnipe and the 143 eldx from my rifle settings the measured drops are not that far off. Would be able to give a better answer with your pressure number.

I don't know what the air pressure is as I don't have a Kestral. Also where I did my testing there was no cell phone or internet service.

 

[John Spadaro]

How close are your scope rings mounted to the turret? The ring clamping too close to the turret is a common cause of turret problems.

Have you accurately input all the parameters into the apps? Scope height exact?

You MV will be slower now that it isn't 85*. You mentioned using RL26 which can get pretty erratic over 80* and now you are shooting 45* cooler. Even if the RL26 wasn't spiking at 85* you still have at least sever fps per degree change.

I prefer to save a new profile for my rifle in 3 temps (90*, 50*, 20*) commonly seem in my shooting. If you are assuming the same muzzle velocity this is likely one of your major errors in data input.

It is possible that the temperature is an issue. I get a stiff bolt lift at 85F, no issue with bolt lift at the colder temp. I should have used my chronometer to test the MV at the colder temp.

 

[Mram10us]

1.5 moa of change at 100 is a lot of environmental change. Doesn't add up to be temp, pressure or anything but hardware.

 

[John Spadaro]

1.5 moa of change at 100 is a lot of environmental change. Doesn't add up to be temp, pressure or anything but hardware.

If the RL26 is causing a heavy bolt lift at 85F, maybe the pressure and MV is higher. What puzzles me is that the drop at 600y is exactly what the ballistic calculator say it should be for a MV of 3105.

 

[LongBomber]

If the RL26 is causing a heavy bolt lift at 85F, maybe the pressure and MV is higher. What puzzles me is that the drop at 600y is exactly what the ballistic calculator say it should be for a MV of 3105.

Think you have two seperate issues there. One was a shift in poi for some reason (scope or load). And then the other where your fired data doesn't add up to your drops.

The drops- even playing around with all kinds of air pressure you wont make up the difference in the 300 and 400 yard data. To be that flat at 300-400 then hit the 600 yard drop number you would need to have a really high mv and a significantly lower bc.

 

[dfanonymous]

Yes, how did you know?

MSL in your original post was a give away.

Your the second pilot with this problem in a month. I'd start by not using any of those weather stations you're use to or anything you'd find on a sectional chart, airmans, metars or taf.

Get a kestrel or use a DA chart with a gps and some way of getting temp.
Pm if you want a analog DA chart, I put all my old military dope references on a share drive on my computer. You can probably find one on google too.

 

[X47guy]

I knew I'd run into one.... you are ignorant to my fundamentals. Have you seen me shoot? Keep your ignorant comments to yourself.

What you do prone isn't repeatable to a bench. What you do with one bag isn't repeatable to another bag.

I don't have to see your fundamentals to know you don't have any. Believing that POI change is normal from position to position is ignorant.

 

[X47guy]

@Holycity73

 

[FURMAN]

it changes because you have poor fundamentals. POI should not change moving from prone, standing, kneeling, off a bench, off a tripod, off a bi pod etc. If you change a bi pod then you can create a different flex on the stock. In a properly bedded stock, it will not change.

Stop typing this in this forum. You are flat WRONG. POI will shift depending on a number of things outside of your personal form or fundamentals PERIOD.

 

[Capt RB]

When I've used the 4dof for firing solutions it can be a click off but not 2 moa when I use the bullet from their library. If your load is 1/2moa at 100yds you should be touching the line of adjustment at every line.
If your zero was with the magneto speed on shoot it again without it. The box test and tall target test will confirm if the turrets are repeatable. One common problem is the vertical split rings. If you have this style do a google search. If not order one and confirm your scope tracking
https://www.boxtobenchprecision.com/target-instructions-2

 

[FURMAN]

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.

Being off that far is NOT your calculator. Sorry if I missed it but what is your shooting setup?