6.5 PRC Ballistics - drops don’t match ballistics chart

[jdmecomber]

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.

John I just tested a VX 6HD. The turret tracking was off around 4-5%. Pm your address and I will send you something to test your scope at 100 yards.

 

[X47guy]

Maybe I should re word poor fundamentals into inconsistencies in your shooting form going from a bench, prone, modified prone, truck hood etc.

Does that ease the minds of some of y'all? Make you feel better?

 

[nt7332]

That is way better wordage. Hurt feelings coming in 3.......2........1.......go!

 

[Mram10us]

I am trying to simply grasp logic here as I have never seen POI shift from a bench to prone or truck hood or whatever. Changing a bipod changes poi? If u have a correctly floated barrel with no contact how does changing a bipod change poi, it's simply holding rifle up. Changing bags, what does that matter again if using same cheek and palm pressure. I am just trying to understand as a rifle and a scope are mechanical objects in which u are simply adjusting to meet the same plane at a given point. I don't see how any of that would change poi if all parallex is adjusted out in each different position. Just a newbie trying to learn

The primary reasons in my experience seem to be rear support firmness(padded case vs rock) and distance of recoil into shoulder (5 coats in cold weather). At short range with light kickers you don't see it. At long range with my edge, you better have your fingers pulling that stock into your shoulder slightly and a firm rear rest or that sucker is going to spine everything you shoot at. At 1000yds it only takes the rear of the stock dropping an extra .015" to shoot a foot higher than normal (check my math, I'm going off of memory)

 

[FURMAN]

The biggest reason is a rifle can slide on a front rest. No matter how good the bipod is it still wants to rotate around the moment created at the attachment to the stock. It is physics. You could get around this with a fclass style bipod with sliding feet on a board but no one is going to carry that into the field. You can argue all you want but it is a fact. What Mran10us is discussing is a completely different aspect of poi changes.

We really need to stop discussing this and get back to letting people help the OP because I do not believe this is his problem.

 

[WiscGunner]

Sounds to me like data is incorrect or scope is hosed.

G7BC of bullet in G1 instead perhaps? Not sure what bullet the OP is using

RL26 from Overtemp to a drop of 45degrees is certainly a contributing factor.

rifle zero'd with magnetspeed installed compared to uninstalled

A screenshot of your app rifle data could help eliminate issues with incorrect data

 

[dfanonymous]

Maybe I should re word poor fundamentals into inconsistencies in your shooting form going from a bench, prone, modified prone, truck hood etc.

Does that ease the minds of some of y'all? Make you feel better?

You're just incorrect if we are splitting c_/t hairs. Your shooting position changes your muzzle velocity slightly as well as the harmonics of your shot.

 

[vancewalker007]

I used a Magnetospeed V3 for MV at Sea Level and 85F. ES is about 10.

I've used a Magneto Speed for 5 years and I've never not had to tune the MV when checking drops at long ranges. The Magneto Speed will put you near the answer but the only way to get to the real number is to shoot long range and tune your DOPE to the results. The Mavnrto speed is much better than the older optical chronys but both are just a starting point. Then, on top of the error in the chronograph your scope will have a certain amount of variation, no matter how expensive it is. You nullify all these errors by physically shooting and recording everything including the environment.

A perfect example is this year's prep for sndcElk hunt. My son's 7LRM showed 3011fps at the muzzle. Shooting at 500 and 1000 with this data showed he was low. We had to tune down to 2970 fps in the G7 ballistic tool to be due on at 500 and 1000. 2 months later my son easily killed an elk at 1090yards. Some of the error was likely in the scope some in his shooting style and some in the Magneto Speed.

 

[Mram10us]

Maybe I should re word poor fundamentals into inconsistencies in your shooting form going from a bench, prone, modified prone, truck hood etc.

Does that ease the minds of some of y'all? Make you feel better?

My shooting is with long range hunting rifles( 28nos, 300rum and 338edge) from 10-13lbs. They aren't 17lb 6br types. You can't shoot those consistently off a bipod in field conditions with poor fundamentals. Not saying I'm perfect, and I will always have room for improvement. That being said, all of those calibers have different poi at 1000yds from bench to bipod EVERY TIME I test them which is a lot. This isn't from reading about others, it is from ACTUAL experience. Sorry OP, back to your topic

 

[jdmecomber]

John

Here is a Vx6HD out of the box with a solid zero....

It was dialed 32 moa and travelled 35.38 inches. 32 moa is 33.504 inches.

 

[Mram10us]

Mr Spadaro,
Have you figured out your issue? Any chance you can make a bit of time to ting a rock when you get to Montana? Hope the shooting session is going well

 

[John Spadaro]

Mr Spadaro,
Have you figured out your issue? Any chance you can make a bit of time to ting a rock when you get to Montana? Hope the shooting session is going well

I went the 100y range today. Temp 83F. I started with a POI test with the last zero I used in the colder temp and higher elevation. The impacts were high by the same amount that I altered my zero for the elevation and temp change.

I did a tracking test on the VX - 6 scope. At 10 MOA the POI was 10.75", 20 MOA = 22', 25 MOA = 27.375". I also tracked R 5 MOA= 5.375", L 5 MOA= 5.5". Returned scope to zero and POI was good.

I also checked MV of frozen cartridges vs warm. The MV cold 3047, 83F warm 3089. The POI shift between warm and cold was 0.5 Up and 0.8 L.

My take on all this is that nothing is wrong with the scope, rifle, or mounts. The environmental changes caused the POI shift. I will need to re-zero again when I get to Montana.

I still don't understand why the drops do not correlate with the ballistic trajectory. Since the scope wasn't dialed between shots, it was not part of the equation. The only thing I can guess is that my bullet was shooting flatter out to 500y and the 600y drop was an anomaly. If I had shot groups I might have gotten more confidence in the data.

 

[Mram10us]

How many shots did you take at 500 and 600 last time? Sorry if I missed it

 

[John Spadaro]

How many shots did you take at 500 and 600 last time? Sorry if I missed it

One shot at each distance. Then I set the scope turret to 9.75 MOA and shot 3 rounds prone off the bipod. 3 Shot average impact was 12" high