6.5 PRC Ballistics - drops don’t match ballistics chart

[Canhunter35]

If you think about all the variables involved, sometimes it's a wonder that we hit our animal...even though our POI changes with different shooting positions, thankfully it's obviously not enough to matter THAT MUCH and that's what we need to keep in mind, have fun, and not obsess so much.

I obsessed for a long time about this but I finally figured out what my biggest shooting flaw is....changing cheek pressure. I will shoot 2 or 3 clover leafs then but the next one 1/2" low and to the right (I'm lefty)
If I shoot enough at one target, oftentimes I can see 2 different groups.

try to figure out what's going on and go from there

Cheek pressure and palm pressure in your grip changes can both make the two group poi

 

[nt7332]

so why can Jim See, Kevin Shepherd, Buck Holly continue to do it? We shoot smaller cartridges for the recoil management and spotting. It's a lot easier to manage recoil on a 6 BR than it is a 6.5x47L. Weight will hide fundamentals also. The bottom line is our POI doesn't change when we change position. If our POI changes, it is something we missed whether be on the reloading bench, environmental or fundamentals.

Don't they give u guys a few sighters before each stage starts like in F-class? Lol. Guess u better zero your rifle instead of prone zero it on a barricade from now on.

 

[colton newsom]

I would try and get out to a range from 600-900 yards dail up your MOA for either range shoot and adjust till you are hitting bullseye at that range then adjust your muzzle velocity until your MOA matches what your scope was dialed for that will give you a true trajectory validation and muzzle velocity 900 yards is best if you can get out that far!!

 

[David Urasky]

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.

Well going up in elevation will give you less drop, but 2700' should not cause a change of 2 minutes at 600 yards. I live at 7000' and have shot at Ben Avery which is at 1500'. My 308 200gn Berger at 2650 FPS only changes 1.5 min at 1000 yards. I think you have other issues.

The bullet path will be consistent and not vary at different distances. If it shoots high at 600 it will be high at all distances. You said your zero changed by 1.5 min at 100 yards? That says there's something else going on. Check your scope mounts, action screws, barrel float, etc.

 

[skipglo]

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.

I use STRELOK Pro.... it's a very good program but like all programs you need to input your values accurately. I has real good starting points but once you shoot with it it gives you areas to true the accuracy of your actual shots and corrects it's self accordingly for your results. Free for Android...costs about 7.00 for iPhone and only about 15.00 to upgrade to the next level. It's a one time price and has free updates as more info comes from the owner...
Good luck!

 

[nt7332]

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

 

[John Spadaro]

Real quick...
POI can shift due to anything from ammo and brass to temperature and support system. Testing should always be done in a controlled environment using the same shooting position, support system and if possible, atmosphere(Indoor for example).
trusting load data from a manufacture is a nice place to start. The real data comes from load development to the specific rifle only. Load data must be proven true. The ONLY way to do so is through shooting at known distance.
Everyone wants to pretend that their numbers are set in stone once a rifle is dialed. This is far from true.
You POI is subject to the world around it once it leaves the barrel.
Using a tripod for testing shows poor fundamentals in regard to a baseline, that's all. Adding more variables for failure proves that. Bench or prone with good support fore and aft for load data are best.
Now as for real world applications once development has concluded, I encourage everyone to shoot as many positions with as many support systems as possible. It makes you a better shooter AND prepares you for the INEVITABLE POI SHIFT.
I would never attest to a shooters fundamentals, or lack there of, without spending range time together. what I can easily attest to is the frustration of the forums telling you what you're doing wrong and even more rarely, right.

Go shoot your rifle as much as possible. Get a good shooting partner. Go out and kill stuff.

ps, I run a 6.5PRC with stellar results. Did no one ask how many rounds the op has through his barrel? Mine sped up significantly around 90 rounds... and the POI shifted

I have 350 rounds down a Proof Carbon barrel. All of those rounds were for load development, practice, and a long range shooting class. I am confident in my loads with the exception that all the load development was conducted at 100y at 85F.

 

[Capt RB]

I have 350 rounds down a Proof Carbon barrel. All of those rounds were for load development, practice, and a long range shooting class. I am confident in my loads with the exception that all the load development was conducted at 100y at 85F.

What is your sd and es of your load? Do you have the same sd at the cooler temps? I've shot 7#s of Rl26 from -18F to 55 with little effect but it is notorious for above 80 degrees changing dramatically.
I'm asking this because short of your barrel going south or a bad optic bedding issue it doesn't add up
How far has your throat moved since it was chambered?

 

[Holycity73]

I have 350 rounds down a Proof Carbon barrel. All of those rounds were for load development, practice, and a long range shooting class. I am confident in my loads with the exception that all the load development was conducted at 100y at 85F.[/

At 350 you're bound to have a variation in speeds from the early testing.

 

[John Spadaro]

What is your sd and es of your load? Do you have the same sd at the cooler temps? I've shot 7#s of Rl26 from -18F to 55 with little effect but it is notorious for above 80 degrees changing dramatically.
I'm asking this because short of your barrel going south or a bad optic bedding issue it doesn't add up
How far has your throat moved since it was chambered?

 

[Canadian Bushman]

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

Some bipods (Harris) allow a good bit of forward and rearward movement. Some do not ( Atlas ). If the rifle is trying to go back but digs into the dirt and cant, its gonna shed that energy somewhere else. It may try to roll, it may hop.

Same with a bag. Hard bag to soft bag, now the butts gonna try to drop as the rifle moves back.

The bigger the bullet, the more recoil, the longer the bullet spends in the bore, the worse all this gets.

small bore little humdingers, not so much.


The further the target the worse the shot becomes.

 

[John Spadaro]

I didn't measure the MV at the colder temps. At SL and 85F my SD is 6 and ES 12. I am going to a 100y range today and will try shooting ammo that is at 32F and measure the MV and see if the POI changes.

The rifle is a custom built on a Origin Action, AG Carbon Stock, action and recoil lug bedded. The rings are Seekins and properly torqued.

The rifle is holding good groups. I will also check my scope tracking today at the range.

 

[John Spadaro]

At 350 you're bound to have a variation in speeds from the early testing.

I tested the speeds just prior to this trip. The speeds are stable but all the testing was done at SL and 85+F.

 

[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.