So I know most just about all ballistic calculators will adjust muzzle velocity according to actual elevation correction data that the user can input into the MV truing option, but are there any ballistic calculators that will adjust or true the BC based on actual elevation correction data another words what if the MV is correct, but the BC is off?
Truing Muzzle Velocity vs Truing BC?
- Thread starter Steel+Killer
- Start date
None that I'm aware of, other than Field Firing Solutions, have a ballistic coefficient calculator. That said, you can manually adjust it yourself. I started playing with the new DTACs which advertised a 0.620 G1 BC. I was hitting high at 1040yds using that BC.
While some companies say just true the curve by adjusting the MV I believe today's Chronographs are much more reliable than in years past. I don't see the point of changing a known variable to something we know it isn't to bend the curve.
So I noted the difference and adjusted the BC till it lined up. Then I tested it again at the same distance on another day with a waterline on the target. It was right where it should be.
While some companies say just true the curve by adjusting the MV I believe today's Chronographs are much more reliable than in years past. I don't see the point of changing a known variable to something we know it isn't to bend the curve.
So I noted the difference and adjusted the BC till it lined up. Then I tested it again at the same distance on another day with a waterline on the target. It was right where it should be.
Applied Ballistics Calculators true based on the location of the SHOT (Distance) or the feature you pick. Such as MV Cal vs DSF. AB Analytics does this as well.
I know there will never be a ballistic calculator that is going to be 100% correct 100% of the time. Honestly I am amazed at how close they can predict already, but like LawnMM said if we know the MV is correct seems like trueing the BC just may get us one step closer to being as correct as it can be.
I have tested my MV but it never got me on target for the curve but when i adjusted the MV to match the down range hits it wouldnt match the closer hits. i played with the COF and that made it line up a lot closer to actual.
It comes down to the question of how reliable is the velocity measurement? Given that most chronographs are only within 1% of actual, making a change of a percent or so is not really changing a 'known' value. Changing the BC is the same thing, that number was generated in one of several different possible ways, all with some potential error factor compared to the same bullet from your rifle.
Where people get into trouble is getting a velocity of 2800fps and a well established projectile and BC value of .475 and then altering their inputs to 2712 and the BC to .522. That's obviously wrong, given what the error margin should be in the measurement values. Any tweaking beyond about 1% of the measured value should raise alarms in the reliability of the original values. I don't know exactly what's wrong, but something is screwed up. Maybe it's the original zero, perhaps the scope has a hitch in adjustments or is just not calibrated correctly, there can be range and angle errors and simply having enough good rounds in a group to find the actual mean impact point. We deal with this a lot in the XLR class
Where people get into trouble is getting a velocity of 2800fps and a well established projectile and BC value of .475 and then altering their inputs to 2712 and the BC to .522. That's obviously wrong, given what the error margin should be in the measurement values. Any tweaking beyond about 1% of the measured value should raise alarms in the reliability of the original values. I don't know exactly what's wrong, but something is screwed up. Maybe it's the original zero, perhaps the scope has a hitch in adjustments or is just not calibrated correctly, there can be range and angle errors and simply having enough good rounds in a group to find the actual mean impact point. We deal with this a lot in the XLR class
I've been thinking the same thing. Waiting to go back out to the range to test my theory.
Same thing happened to me trued at 1000 and then was off at 800 using match grade ammo and roughly same temp and da with a kestrel. I've read bc changes with velocity so I'm going to play with it and see if it's a little closer!
Ok went back out today shot 10 rounds over the magneto. Gave me a mv of 2790 put that in my kestrel. Zeroed at 100 and then went out to 810 (longest i had available) kestrel said 6.08 for elevation. 5.8 was above center and 5.7 was below center. So i trued the velocity in the kestrel with 5.75 mils at 810 yards. Gave me a mv of 2731. Is it really possible to have 60 fps difference from the magneto speed. Been told the bc of 330 on the 140 grain rdf bullets was gtg. Am i wrong to think thats not the case? Im loading 42.6 h4350 50 thousand off the lands. Avg mv was 2790 and Sd was 8.4. 2 rounds at 810 had a vertical of less than .25"
Interesting...using the RDF 140's I had a similar result this past weekend, where my 700yd impacts were .2 mil's higher than expected using the .330 G7 BC. I was thinking maybe a temperature change (zero'ed in the morning before the match, with the last shot being about 11:30 and 25-30 degrees warmer), but I may have to go back out and play some more. I didn't see this out a Tikka .260 using this bullet, so I'm scratching my head a little...
yea the above scenario was something in my kestrel that was messed up. cleared it out and started over. everything seemed to be on the plates from 330 to 1320 with the exception of 700 yards. It took a .1 mil to get it back on the plate. Probably could have been .2 but I had limited rounds to shoot so I didn't take many shots at 700. Dope for 300 400 500 600 and 800 890 1000 1050 1240 and 1320 was correct.
There is defiantly something in that midrange that's a little funky and I could have been hitting the at the top or bottom of the plates at 600 and 800. next time I will go out and put some fresh paint on the targets so I can see where its hitting.
Did you try g1 vs g7? Would think bc would be more accurate than mv as there are so many factors there or the tolerance stack of density and mv and distance, given most my equipment would have a wider band than those that Doppler test.
