Drop chart issues

[Retterath]

I went out shooting tonight and want to see how my gun was grouping at 550 and 1000. I'm shooting a 7wsm 168 Berger 2905fps G1 bc of .617. I zeroed my gun three weeks ago and also shot it through the chrono and didn't shoot it till tonight. My shooter program had it at 9.7 moa at 550 and after shooting my actual dope was 8 moa. I shot a 2.75" group at 550 so it shot good. Now at 1000 shooter program said 25.3 moa and my actual dope was 23 moa and then shot a 7" group at 1k. Why would my drop chart be so far off?

 

[Justin Crossley]

Your velocity is higher than you input probably.

 

[Retterath]

I checked that and I entered it correct. I added another 100 GPS in the program and the 550 is really close but 1k is still off quite abit.

 

[Justin Crossley]

I would guess that your velocity is about 2960 fps.

 

[Justin Crossley]

What were your conditions?

 

[Retterath]

70 degrees no wind and pressure 27.86

 

[Retterath]

I zeroed my gun 3 weeks at100 yards and then also shot it at 200 and the elevation and wind age was good. When I shot at 550 my wind age was at zero and was fine. I let my barrel cool and shot at 700 and I was hitting way right. Still no wind. So I went to a 1000 and shot and was shooting almost 2 feet left. Still very calm then adjusted 3 moa left to center. I'm also confused on that whole wind age also

 

[cowboy]

Are you using an anticant bubble? Is this being shot off a bench or prone with a bipod?

 

[Retterath]

Prone with a bipod. I don't have an anti cant but was trying to make sure it was level and not canted.

 

[josef]

Did you set your scope height in your ballistics program? Also have you shot it again at 100 and made sure there wasn't a zero shift? It's interesting that the spread is close to equal. Not sure you would see that in an error in atmospheric or chrono errors. Just some ideas. Good luck with your trouble shooting.

 

[RosinBag]

On your wind age issue, your scope may not be levelled correctly or you induced can't in it.

For the elevation to be that far off, 23" at 1000 yards, something in your program isn't matching up with your environmental conditions. I will double check all your input data.

 

[RosinBag]

I just ran your specs in Bullet Flight. 550 showed 9.7 minutes and a 1000 showed 25.1 that is with a 100 yard zero and 1.8" sight height.

One thing I noticed when looking at the ballistics. Maybe your range was off. If it was 500 and 950, your numbers are really close 8.0 is 490 yards and 23.0 is 948 yards.

Sight height alone won't give you the large spread between your actual dope vs computer dope.

Velocity in combination with ballistic coefficient could though.

 

[fire arrow]

Were you shooting across canyon, and if so what time of the day was it?

 

[RosinBag]

Also, was it uphill or downhill? I think this is a distance to target issue since both yardage were off by nearly the same distance. Hopefully the OP will let us know what the issue was on this.

 

[KMD]

First things, first.

Have you tested your scope to confirm it is tracking true throughout that adjustment range?
Some scopes will track well for a bit, then begin to wander off the reservation with increased erector travel.

If you haven't confirmed that your scope tracks true, then address THAT variable, first & foremost.

 

[Retterath]

i checked my program over and over and there was no shooting across a canyon or up or downhill shooting all flat. my sight height is 1.75
I ranged the targets multiply times to make sure. Im going to have to go and shoot at a 100 yards and make sure my zero is correct and also going to do a box test to see if my scope isnt tracking right. Im shooting a mark 4 lrt.

 

[Whisky]

Yup, confirm zero first....then box test. Shoot through a different chrono if you have access.

, what BC drag model you using in Shooter, G7 or G1?

This is against the grain I know, but for me I find G1 more accurate in Shooter for some reason, even shooting Berger

 

[KMD]

Ah, the dreaded Leupy rears its ugly head at distance...

What you're seeing is the scope is likely adjusting MORE than the listed .25moa per "click" toward the end of the erector's travel.

From what you described, out to 550yds, each 'click' is adjusting .25moa accurately. But with the increased erector travel needed at distance, your scope might very well be moving MORE than .25moa per 'click'. That's why your needing LESS correction to hit @ 1K. Common occurrance with Leupys...

Its not the end of the world, IF THE SCOPE tracks REPEATABLY. If you're consistently needing 23moa to hit @ 1K, and the scope returns to zero perfectly, then simply modify your dope card to reflect what THAT scope needs to hit @ 1K. In essence, you're "truing" your dope to accommodate the incorrect adjustments of the erector. Just prove it and make sure you're dope stays consistent...

In that regard, a scope can still remain usable as long as it tracks REPEATABLY. The clicks don't have to allow an exact .25moa of movement, but the error needs to be CONSISTENT. Otherwise, the scope is total junk & truly needs repair.

 

[Retterath]

thanks for the great advice guys. i will box test this weekend and see what happens

 

[Sam Millard]

thanks for the great advice guys. i will box test this weekend and see what happens

Don't waste your time with a standard box test. Plumb a line to at least 20" (check your backstop), get your zero nutted, then dial 20 MOA on the scope and see if the impact is ~ 21". Run it back to zero to make sure it returns. You can also fire rounds left, right, and anywhere in between 0 and 20. Just remember to factor 1.047" for MOA.

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