What could cause my dope to be off?

[7magsavage]

Ok. It's no big deal but it's driving my crazy. Can't figure out why my dope is slightly off with everything being so accurately accounts for.

6.6x47L. Berger 140s. H4350.

MV via V3= 2746
target distance 433 yards.

My Shooter app which has always worked well for me gives me 7.5 MOA

At 7.5 MOA come ups I am 1/2 MOA low.

I have to dial 8.0 MOA to b dead nuts. I guess that's why they call it data on previous engagement, but never had to tweak MV in the app to make my drops match with the 6.5 before.

Any thoughts?

 

[lash]

Whats different about this load from others you've been successful with? New projectile?, Any changes to your rifle system? New Scope?

What about environmental inputs? Temperatures/pressures any different from what is on your app?

How about your results at other distances? Are they different from the app?

 

[7magsavage]

Nothing new. Only had one distance to shoot at.
Drops out to 1000 were SPOT-ON before.

 

[demolitionman]

Match to match my vertical dope for the same targets can vary as much as 2 to 3 tenths of a mill. My most obvious factor is my ammo temperature. If it's raging hot out my "usual" dope shoots too high but its not so noticeable inside 400 yards. I shoot your exact load and my come up is 7.5 moa..... as well. Re check your zero? Maybe your scope isnt returning to center....

 

[7magsavage]

Checked zero right before. Put a 0.75" dot on a piece of paper and put three shots inside the dot. Called it good. Went to 400 and shot. Noticed that my impacts were low on the steel. Came up .5MOA and was spot on.

Leaving for for a match this evening and don't have time to play with it. I know it's .5MOA, but in my opinion that's the difference between a hit and a miss at a hard/far target.

 

[lash]

So, if everything is exactly the same as before when you shot this same load in the same rifle at the same place, then your dope is not off. Something changed that affected your calls on that day, but if everything was spot-on before then it's not your dope. Like I said, environmental inputs or something else may have affected your poa/poi relationship. Temperature? Mirage? A different lot of powder? Loose scope mount or rail? Scope failure onset? Bad fundamentals that day?

 

[7magsavage]

The only thing I can think of is that I needed my longer bipod to be more comfortable. I had a good sight picture but I may have been muscling it more than I thought.

 

[demolitionman]

If you check zero off a bench then end up shooting prone that creates a very different poi for alot of people. I learned that real quick. If u plan on shooting prone zero prone. If u havent done that of course.

 

[7magsavage]

I always zero prone. And was shooting prone at distance. Thinking maybe just my position. We shall see tomorrow.

 

[JBM_DC]

So this thread lacks a ton of information.

A few things that come to mind.

Check to make sure you have your scope height entered correctly. Dope at 400 yards really should not change much at all.

Does your scope track properly? What scope are you using?

Check to make sure everything on your rifle is torqued properly. Action screws, scope base, scope rings. Check everything!

Check to make sure you have the correct BC for you bullet G7 or G1. This also is a bit dependent on your twist rate as well.
(140 Hybrids in my 8 twist at 2730 I used a G7 of .307 confirmed out to 1400 yards)

How many rounds did you fire to obtain your average muzzle velocity? (I usually fire 10 rounds before every match to check velocity)

Also I have always found Shooter to be slightly off and have since moved on to Strelok or Kestrel with AB. Both of these give the same values where shooter would vary slightly.

 

[7magsavage]

Scope height precisely measured.
Have shot this load from 400-1000 yards in 100 yard increments and was spot on.
Scope is a FFP Nightforce ATACR

I used the BC that automatically is entered into the bullet library for Shooter which is 0.319. I put your number of 0.309 in and it bumped me up to 7.6 MOA dope. So, going in the right direction, but still doesn't make up the difference.

 

[demolitionman]

Shooter has a velocity calibration option where you can enter your impacts @ distance and the software will adjust your velocity. This type of truing is probably more precise than shooting over a chrono .... of course this doesnt help if you don't have time to re-true your dope.

 

[JBM_DC]

Shooter has a velocity calibration option where you can enter your impacts @ distance and the software will adjust your velocity. This type of truing is probably more precise than shooting over a chrono .... of course this doesnt help if you don't have time to re-true your dope.

If you are 100% sure on your velocity I am not a big fan of adjusting it in a program to match what you are seeing down range. Especially only at 433 yards. Something else could be going on here. Where you shooting in a STRONG cross wind?

 

[7magsavage]

I have had excellent results with making it match in the past, but I'm not convinced that's what I need to do. I don't want to change so much before a match. I will likely shoot it as is and see what happens. It could have easily been my body position I suppose.

 

[lash]

If it were me, I'd not change things before a match. Just pay attention to your impacts early on and only adjust if things are off in a consistent manner.

 

[7magsavage]

Yeah man I'm with ya. I'm not changing it up. Just going to do exactly what you said. Shoot it and see what happens.

 

[lennyo3034]

I am having the exact same issue except at 600 and 700 yards with 7 mag. Multiple ballistic calculators say I needed 2.5 mils at 600. Ended up needing 2.7.

Tracking on my scope was spot on, as was zero when I tested it at home the next day.

The only thing I could think of is bipod hop. When zeroing at 100 I shoot off of a hard surface. When I was shooting st distance, I was shooting of soft ground. If my rifle was hopping while zeroing but not while shooting at distance, that could do it. But that is just my theory.

 

[7magsavage]

I don't think hop is as likely of a cause as just varying cheek pressure and body position from one shooting position to another.

 

[lash]

Frank did do a tutorial one time about the differences in impact when on a bench versus prone.

Here it is:
https://www.snipershide.com/muzzle-velocity-variation/

 

[demolitionman]

If you are 100% sure on your velocity I am not a big fan of adjusting it in a program to match what you are seeing down range. Especially only at 433 yards. Something else could be going on here. Where you shooting in a STRONG cross wind?

I agree JB. I definently dont recommend adjusting your velocity according to one single known distance target. Now a run of targets out to 1000 will tell the story.

 

[JBM_DC]

I agree JB. I definently dont recommend adjusting your velocity according to one single known distance target. Now a run of targets out to 1000 will tell the story.

I still wouldn't adjust my velocity and never have needed to. I always play with the BC first, but there are many more variable that dictate elevation changes in a ballistic curve than just BC and Velocity. Though for those without a chronograph truing dope is a helpful tool.

 

[JBM_DC]

Yeah man I'm with ya. I'm not changing it up. Just going to do exactly what you said. Shoot it and see what happens.

Just shoot with an open mind and dont try to force anything to happen. Hopefully you will be able to see your misses and make subtle adjustments. GL at your match!

 

[lennyo3034]

I don't think hop is as likely of a cause as just varying cheek pressure and body position from one shooting position to another.

You're right. I went and tested and made no difference on POI at all.

I went to 1k yesterday and was significantly off from what shooter was telling me. A 7 mag needed .4mil more than calculated. A 6.5CM needed .7mil more.

I downloaded strelok pro and Applied Ballistics. Strelok matched shooter almost exactly. AB was even further off.

If you figure out why yours was off, please share as I am seeing the same thing.

 

[7magsavage]

So, here's my update:

I went and shot the match. Didn't screw around with anything. Just used the MV that the V3 gave me and my dope was spot on. Evidently at my home shooting locale was just muscling the rifle and using bad fundamentals. I shot at targets from as close as 230 yards to as far as 1000 yards with hits. I was glad I didn't go and try to reinvent the wheel. It would have been ugly.