Getting ready for a cow elk hunt. Taking my 7mm Practical, 180gr ELDM over 87grs of US869 powder. 5 shots across my magnetospeed showed 3063,3067,3071,3097 and 3089. Avg of 3077 is what I got. My issue is if I input those inputs into Strelok the data it puts out don't jive with actual shooting results. I'm just charting my actual come ups in MOA and going to go with actual shooting results rather than calculated data but I'm not sure why? Strelok data works for my 308 and my 30-338 Winchester, but this rifle has always seemed to not line up with what the info says. I may perform a box tracking test on my scope. That's the only thing I can think of is the 1/4 MOA clicks are not moving 1/4 MOA. It seems to return to zero fine though. If I dial to a yardage and come back to zero my 200 yard zero seems to repeat. Nikon X1000 Black 4-16x50. Think I'm barking up the right tree?
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Ballistic calculator issues
- Thread starter cgarb
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ShtrRdy
Well-Known Member
The scope is possibly the culprit. You may want to do a tall target test to get a better idea of tracking.
Do you have a good measure of the distance between bore and scope centerline?
Do you have a good measure of the distance between bore and scope centerline?
Yes, centerline of the barrel to centerline of the scope ring is right at 2". I'm assuming that measurement don't have to be a 3 place decimal to have somewhat accurate data. I would probably want it as close as possible if I was trying to achieve a cold bore hit at 2000+ but I'm not capable of shooting that well. 600 is my limit, I feel I can make that shot in field conditions enough to hit elk vitals. It's not fair to the animal for me to try any further unless I get some trigger time beyond 600.
So posted BC is just Posted… if you're confident in your scope height and your velocity, there is only a handful of other variables in the equation. Temp, air density, wind, elevation, consistency of load work up, factory or hand loads, SD and ES ext. I do not rely on posted BC. It is based off an average of barrel length, velocity, powder charge ext. Typically sea level elevation. Barrel twist, velocity, elevation all play a role in your ballistics being correct. I personally do not true my ballistics inside of 800 yards. 650 on most ballistic calculators is very close after 650 you start to see what I refer to as the parachute effect on projectiles. Adjusted BC or velocity values will true your Drop chart. The effects on doing this are very minimal if any inside of 650. If your scope is tracking properly, then you need to adjust the BC value of your ballistic calculator to correspond with what your true dope is on your scope. Trust what you see, not what a computer tells you.
No doubt whatever clicks it takes to get on target is what's getting taped to the stock for use, I was just wanting to know why the numbers weren't even close. As far off as it is, it almost has to be scope related in my opinion. I'll find out next weekend.
Aussie Hunter Steve
Well-Known Member
As stated above, manufacturers BC may not be accurate for a particular bullet. Check your elevation, being several hundred feet out caused me headaches in my less experienced days. If you're stretching past 1000yds coriolis effect will come into play.
ncwg2boatguy
Well-Known Member
You can true your data in the app. But need to stretch it out as far as your gonna possibly shoot it to . Dial the data apps gives you then adjust elevation however much you need in app. Then it will do the math for you. Recheck on target at 200 zero or 100 wherever yours is and walk it out.
Mikecr
Well-Known Member
Most scope makers make generalizations about their adjustments.
So then their MOA is not actually 1.047 inches per 100yds (IPHY).
It's easy to test, and hopefully your software allows you to enter your actual adjustment value.
Atmospherics are also important to BC. You need to account for this.
If anything, check your local airport weather conditions, enter it in software.
Where it gets tricky is your entry of BC. Depends on the software.
Sometimes when you enter BC, it can override local BC. The software may assume that you know that the BC you're entering is correct, right now, regardless of other entries.
Ideally, you would enter factory declared BC and check a block for what air density conditions that BC is based on. Std Metro, Std. Army, or ICAO for example. Then, as you enter local attributes which would affect that BC number, the software would internally adjust BC for that.
Take the time to look into & consider what your software is doing.
BrentM
Well-Known Member
How far off is the app from reality?
What I read is that your chrono'd (assume good chrono), your data for other rifles lines up, and this particular rifle is the only issue. So, it sounds like you understand the external and internal ballastics component and have ruled out user input error.
I would definitely test scope tracking. Had a fellow competitor tell me one of his scopes was around 5% off but returned to zero etc just fine. Once he changed his data to .95 his solutions were on track and he kept using the scope. There is a box test or a line test. I'd think in your case do the litz style line test of 30 moa at 100 and see how it goes. I'd be surprised if this was not your issue.
What I read is that your chrono'd (assume good chrono), your data for other rifles lines up, and this particular rifle is the only issue. So, it sounds like you understand the external and internal ballastics component and have ruled out user input error.
I would definitely test scope tracking. Had a fellow competitor tell me one of his scopes was around 5% off but returned to zero etc just fine. Once he changed his data to .95 his solutions were on track and he kept using the scope. There is a box test or a line test. I'd think in your case do the litz style line test of 30 moa at 100 and see how it goes. I'd be surprised if this was not your issue.
ncwg2boatguy
Well-Known Member
Kestrel is your friend
I would zero the rifle at 100yds, then set up a tall target at 500 yds, annd without adjusting the scope, aim at the bullseye near the top of the target, take several shots, and measure the drop. That's the actual ballistics. To check the scope, back at 100 yds, turn maybe 24 clicks, or whatever is supposed to result in 6 inches high, then shoot several shots to check, and then calculate actual elevation change per click. These two things would give you good information to work with.
BrentM
Well-Known Member
That's too far for a test. Too many other factors can negatively affect it. That is why the tall target test is set at 100. Less external variables for more precision for the scope tracking.
I agree there are variables, but everything can be accounted for to check against the ballistic calculation (muzzle velocity, scope height, temperature, elevation, wind) except the shooter's aim. You can't verify ballistics very well at 100. At 500, average drop of 10 shots being 36 inches vs 42 inches would help validate ballistics, taking the scope out of the equation. 100 yds for the scope check, 500 for ballistics check.
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