Ballistics question

[JayHeater]

I have one rifle that when shooting the ballistic output from either my G7 rangefinder or Applied Ballistics program isn't correct. Using a Labrador for speed, I can normally use that speed for the programs and it's very close if not perfect. Shooting a 30 cal., 215 hybrid target, I get average speed of 3076. SD 5.4, ES 15. Using that and the .354 G7 from berger, the correction is always low. Adjusting the speed to 3030 I get correct inputs. I have not encountered this with any other rifles. I've worn my forehead bald thinking about what might cause this. All inputs are correct setting up that programs. I get the same results using an NXS or a Khales 525. Thoughts or similar experiences?
I appreciate your time and input.
Thanks,
Heater

 

[CharlieNC]

Truing actual drop using velocity adjustment is common, and many ballistic programs provide an automatic function for this purpose. Using multiple range sessions, across various temperature / BP plus lighting conditions, will provide a more reliable adjustment. Evaluate the adjustment at numerous distances, and at extreme may need to tweak BC too.

 

[darkangel_r2]

What twist rate barrel?

Are you sure about your zero?

What range are you shooting at?

 

[Beiruty]

if you have a valid MV from Labradar/Magneeto, lower the value of the G7 BC

 

[JayHeater]

I agree that it's common the adjust the speed some to achieve the best corrections at distance. I've never been in the ballpark of 30-40 fps adjustment though. I'm beginning to think something is going wrong with the bullet as it leaves. This rifle groups extremely well.

1 in 8 on the twist.
The zero is perfect.
I shot it at 800 and a 1000 yards.

Thank you.

 

[CharlieNC]

Have you experienced this on more than one day? Sometimes the conditions and lighting give quirky results that don't repeat as extremely on other days.

 

[JayHeater]

What would be a good method to adjust the BC if I'm confident the speed is good?

 

[JayHeater]

I've had the same issue since I had this one. Last year was the same issues. I reworked the load over the summer running it faster with better numbers. Same issues.

 

[6ShotsOr5?]

if you have a valid MV from Labradar/Magneeto, lower the value of the G7 BC

+1

 

[bmx]

IMHO all the programs and simulations are ok for getting in the ballpark but the best way to get the correct drop readings per yardage is to shoot in actual conditions at the specific yardage over several different days then average the results. When going from say the midwest to Wyoming or Montana elevations l always re-zero my rifles.

 

[Jarhead6870]

Chronographs have a percentage of error. I typically true my MV at 600-700 yards and then true the BC at 1000 yards plus. Distances need to be precise as does scope tracking.

 

[Fergus McLaggin]

I have noticed variations from the modeled algorithm in multiple ballistic programs for the same set of inputs. You can have everything correct for the instant the shot was taken and a variation occurs. You have to remember these are just programs, making computations for a set of parameters. The only way to assist the algorithm in the solver is to provide actual data of shots made from various ranges. For example, the Applied Ballistics app has the option of purchasing Custom Drag models where you can pair your results for a more precise result from the app. The Ballistics ARC app allows this function as a standard option of the app. I love and use multiple apps all the time, however, my personal belief is that no matter how good the app is there is no substitute for real range data.

 

[NZ_Fclass]

I have nothing too sophisticated, but using a Magnetospeed get a muzzle velocity, put it into JBM, then sight in at the range. I record the changes to JBM's estimate in a notebook for each range that I shoot at, using the scope set on a 500yd zero ( not all ranges are "true" lengths, but most 500's are pretty close). Works well enough without resorting to much technology.

 

[JayHeater]

Jarhead,

Your method makes sense to do both. Is there a starting percentage you adjust the BC down once you've done the speed work at 6-700? Using the G7 of .354, adjust down 10% to .319 to start with? Or, is that to much at once? I've not tweak BC and don't know the reaction of lessening it 5-10%. I need to gain 6" at 1000 using the MV my LR throws.

I appreciate everyones input.

 

[darkangel_r2]

I agree that it's common the adjust the speed some to achieve the best corrections at distance. I've never been in the ballpark of 30-40 fps adjustment though. I'm beginning to think something is going wrong with the bullet as it leaves. This rifle groups extremely well.

1 in 8 on the twist.
The zero is perfect.
I shot it at 800 and a 1000 yards.

Thank you.

berger bullets single g7 number is averaged from 3000 fps down to 1500 fps. Your max range shot only has you down to 1700ish fps so yours is going to be higher than the listed due to this.

But depending on your conditions 10 twist may not fully stabilize 215s. 0 degrees and 0 altitude put you at 1.31 stability factor losing aproximately 6% of the bullets bc. The combination of these two factors can put your true bc anywhere between .365 and .34 g7.

 

[Mauser06]

Jarhead,

Your method makes sense to do both. Is there a starting percentage you adjust the BC down once you've done the speed work at 6-700? Using the G7 of .354, adjust down 10% to .319 to start with? Or, is that to much at once? I've not tweak BC and don't know the reaction of lessening it 5-10%. I need to gain 6" at 1000 using the MV my LR throws.

I appreciate everyones input.

Adjust the bc till your data lines up with the actual data needed.

If you put 26 minutes on the scope to hit, Adjust the bc till it shows 26 minutes at that range.

 

[INTJ]

I agree that it's common the adjust the speed some to achieve the best corrections at distance. I've never been in the ballpark of 30-40 fps adjustment though. I'm beginning to think something is going wrong with the bullet as it leaves. This rifle groups extremely well.

1 in 8 on the twist.
The zero is perfect.
I shot it at 800 and a 1000 yards.

Thank you.

I have seen this several times.

 

[JayHeater]

Thanks everyone for your input. I appreciate the great insight you've given.

Happy Holidays!

 

[PracticalTactical]

I have an analogy that could explain such a variance... Suppose you were shooting a bow and the front arrow rest was perfectly aligned. That arrow will come out of the bow nice and straight, and will fly fast and hit accurately.

By contrast, if you don't have the arrow rest in the correct position, the arrow will kick and flutter in flight and eventually stabilize. It will hit low and will lack accuracy.

So translating the same to a rifle... First, don't assume bullets from both rifles are coming out perfectly straight. Sloppy freebore and other chamber differences can create inconsistencies in muzzle velocity and induce a wobble to the bullet in flight, which increases drag and causes it to slow down more quickly. If one chamber is more suitable than the other, as well as the barrel itself, that could explain subtle ballistic differences.

My guess is the rifle that shoots high is the more accurate of the two.

 

[David Milisock]

I agree that it's common the adjust the speed some to achieve the best corrections at distance. I've never been in the ballpark of 30-40 fps adjustment though. I'm beginning to think something is going wrong with the bullet as it leaves. This rifle groups extremely well.

1 in 8 on the twist.
The zero is perfect.
I shot it at 800 and a 1000 yards.

Thank you.

Shooting East, West, Nort or South?