So I’m posting this as a legit question because I’m learning. I was taught to true velocity at 600 and BC at 1000. It’s pretty much worked out for the most part. I shoot factory 6gt Hornady 109eldm. I’m never confident with it, just because of the vertical dispersion I get at distance. I feel like I need to “true” before every match just so I have a little stress relief beforehand. I recently heard on a podcast or somewhere, I’m pretty sure it was the applied ballistics crew, and if I heard them right, they said true velocity inside 1200 yards. I think they were actually speaking in terms of Mach, like true velocity to Mach 1.2 or something like that. Does anybody have any knowledge on this subject. If I true BC at 1000, it usually drops to around .260, that doesn’t seem right to me. What should my BC on this round be. When should I true my BC or velocity?
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True velocity inside 1200yds?
- Thread starter KYyeeter
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That bullet is actually pretty damn good. Idk about the factory ammo but i shoot that bullet in a 6br at 2720fps and my bc works out to around 287. Ive been using the custom curve for this last match and everything lines up. I know lots of guys true bc but there are so many variables that you can miss read i think its a bad idea. If its high or low ill adjust velocity or zero offset
The box says it’s a .295 bc. Someone told me to run .280. But if I true my bc, it drops to .260ish. So inside these shorter distances, inside Mach 1.2 or whatever it is, what’s the point of truing bc? I’m using Strelok pro. How do you get a custom curve? Off a kestrel?
I thought you were using a kestrel with ab. Are all of your inputs perfect? Bore height is important. Really inside 1000y bc is important for a wind call but if you dont have a wind meter it wont matter. Personally id just do what i had to to make it line up from 100-1100y. Velocity will have a higher effect then bc at those distances. Again make sure all your inputs are perfect or as close as possible
Yea all inputs are good, don’t think ever really paid attention to it before on other calibers, I just made things line up, like you said, and just rolled with it. But now I’m trying to actually learn the “why” behind the data, if that makes sense.
if youre going to shoot a hornady bullet you can get the hornady 4dof app for free and true with the actual drag model for that bullet and compare to whatever youre running now
for ABs CDM i think they recommend truing them around that mach # you mentioned...not sure of the details because ive never used them...but they arent a BC you true like normal..theyre a drag model also
hornady has also put out a few podcasts/youtube videos related to their software and the workings behind way more in depth than i could type here
as far as where to true BC vs velocity, its a give and take on where velocity matters more vs where BC takes over...most standard short action cartridges like youre shooting, 500-600 yds is around that window. in order to move the BC enough to shift dope .1-.2mil @ 500 yds would take a huge shift that would not line up at 1000 yds and further...so you'd opt for a velocity tweak instead
at 1000 yds, a small BC change is going to shift your dope .1-.2mil, but that BC change likely wont even be noticeable in your dope at 500 yds
basically, you are fudging the numbers both ways to make them match a generic drag curve as close as possible. A bullets BC also changes in different velocity bands, thats why hornady's website lists the 3 numbers for most of their long range type bullets, there is a highest (close range, hightest speeds), a middle (mid range), and low (long range/slowest speeds). Using the highest listed BC for shooting 1000 yds wont ever line up correctly. A bullet experiences all of them as it travels down range.
Berger/AB lists an averaged BC that usually matches up very close to actual for shooting inside 1200 yds in my experience
also shooting factory ammo, if not running the same lot # 100% of the time there will be lot to lot variations in speed and bullets...vertical dispersion at distance could just be velocity variations in ammo unless youre already chrono'ing and verifying every different lot
on top of all that...there are small things that affect impacts at distance like lighting/winds that arent easily measured and accounted for. any one who says they just true their dope once and its perfect all the time doesnt shoot much or doesnt travel much. it can change few tenths of a mil within minutes from mirage/lighting/shadows alone if the conditions are right. if youre finding yourself chasing things back and forth, id suggest confirming no lot to lot variations in ammo and then verify any perceived changes multiple days in a row. if its shifting back and forth over multiple days (assuming rifle/scope is mechanically sound) its not necessarily a truing issue youre seeing, its very likely conditions...assuming the shooter is squared away and not producing a bias.
all said, the velocity to 600 and BC at 1000+ does work. When i was competing it was the most commonly used method i know of among the top shooters traveling all over. Sometimes conditions like lighting/mirage/winds forced small tweaks to be made on the fly, but its part of the game.
the hornady podcasts are really great at explaining a lot of the details and factors behind how it all works on the math/physics side
for ABs CDM i think they recommend truing them around that mach # you mentioned...not sure of the details because ive never used them...but they arent a BC you true like normal..theyre a drag model also
hornady has also put out a few podcasts/youtube videos related to their software and the workings behind way more in depth than i could type here
as far as where to true BC vs velocity, its a give and take on where velocity matters more vs where BC takes over...most standard short action cartridges like youre shooting, 500-600 yds is around that window. in order to move the BC enough to shift dope .1-.2mil @ 500 yds would take a huge shift that would not line up at 1000 yds and further...so you'd opt for a velocity tweak instead
at 1000 yds, a small BC change is going to shift your dope .1-.2mil, but that BC change likely wont even be noticeable in your dope at 500 yds
basically, you are fudging the numbers both ways to make them match a generic drag curve as close as possible. A bullets BC also changes in different velocity bands, thats why hornady's website lists the 3 numbers for most of their long range type bullets, there is a highest (close range, hightest speeds), a middle (mid range), and low (long range/slowest speeds). Using the highest listed BC for shooting 1000 yds wont ever line up correctly. A bullet experiences all of them as it travels down range.
Berger/AB lists an averaged BC that usually matches up very close to actual for shooting inside 1200 yds in my experience
also shooting factory ammo, if not running the same lot # 100% of the time there will be lot to lot variations in speed and bullets...vertical dispersion at distance could just be velocity variations in ammo unless youre already chrono'ing and verifying every different lot
on top of all that...there are small things that affect impacts at distance like lighting/winds that arent easily measured and accounted for. any one who says they just true their dope once and its perfect all the time doesnt shoot much or doesnt travel much. it can change few tenths of a mil within minutes from mirage/lighting/shadows alone if the conditions are right. if youre finding yourself chasing things back and forth, id suggest confirming no lot to lot variations in ammo and then verify any perceived changes multiple days in a row. if its shifting back and forth over multiple days (assuming rifle/scope is mechanically sound) its not necessarily a truing issue youre seeing, its very likely conditions...assuming the shooter is squared away and not producing a bias.
all said, the velocity to 600 and BC at 1000+ does work. When i was competing it was the most commonly used method i know of among the top shooters traveling all over. Sometimes conditions like lighting/mirage/winds forced small tweaks to be made on the fly, but its part of the game.
the hornady podcasts are really great at explaining a lot of the details and factors behind how it all works on the math/physics side
That’s some good info. I recently started using the 4dof app and switching back and forth between Strelok and 4dof. There are things I like about both and some things I don’t but they aren’t far off from each other as long as my inputs are correct. One thing I like about 4dof is I don’t have to worry about bc. Just chrono and then true it up at distance but it’s always been pretty close starting off. But you are right about factory ammo, I chrono multiple times per lot. Until I start reloading I’ll just have to deal with it. I’ll have to check out the podcast.
I'd argue truing is only helpful if you don't have an accurate chronograph. It's challenging to account for environmental variables and shooter-induced error with enough fidelity at the ranges needed to true effectively.
If you're using a magnetospeed or labradar, paired with a CDM, that's as good as you'll get without confirming the suggested elevation corrections.
It may be helpful to understand why truing came to be. The military guys getting issued the first hardened pocket computers with ATRAG didn't have issued chronographs (that came later along with AB). We were taught to true so the software could reverse engineer the actual MV of our rifles. Once we started getting issued or buying Magnetospeeds, the need to true went away completely.
I'm out of the military now but occasionally shoot in matches. I run 5-10 shots by my LabRadar the day of the match when I confirm zero and plug my average MV into ABMobile. That's been working well so far.
If you're using a magnetospeed or labradar, paired with a CDM, that's as good as you'll get without confirming the suggested elevation corrections.
It may be helpful to understand why truing came to be. The military guys getting issued the first hardened pocket computers with ATRAG didn't have issued chronographs (that came later along with AB). We were taught to true so the software could reverse engineer the actual MV of our rifles. Once we started getting issued or buying Magnetospeeds, the need to true went away completely.
I'm out of the military now but occasionally shoot in matches. I run 5-10 shots by my LabRadar the day of the match when I confirm zero and plug my average MV into ABMobile. That's been working well so far.
They talked about this on one of the Miles to Matches podcasts a while back... and IIRC the recommended way to get one's actual BC nailed down was to shoot at a known distance target at a distance as close to the point right before one's rounds go transonic.
For most guys shooting cartridges in the 2800-3000fps range, this means a target somewhere around 1200 yards or so, after one already has a chronograph-confirmed MV in that same weather/environment. I've found this works great myself, and ideally, this is the way I like to get things figured out if I've got the distance and mild conditions (luckily my club has targets at 1250yrds and golf carts to drive down there, as some days even the best glass can't see impacts clearly enough from the shooting position at that range).
Truing MV at 500-600 yards, and then the BC at ~1000-1200 yards, working from tested, known-to-be-good data, is like a quick and dirty way to gather MV/BC information for shooting in a different, new and/or untested environment (common differences are things like weather/temperature/altitude), for when you don't have the chrono, ideal range, and/or glass needed to even spot it.
LIke has been mentioned, BC changes with different MV, so without retesting for the new environment/conditions, truing is it.
For most guys shooting cartridges in the 2800-3000fps range, this means a target somewhere around 1200 yards or so, after one already has a chronograph-confirmed MV in that same weather/environment. I've found this works great myself, and ideally, this is the way I like to get things figured out if I've got the distance and mild conditions (luckily my club has targets at 1250yrds and golf carts to drive down there, as some days even the best glass can't see impacts clearly enough from the shooting position at that range).
Truing MV at 500-600 yards, and then the BC at ~1000-1200 yards, working from tested, known-to-be-good data, is like a quick and dirty way to gather MV/BC information for shooting in a different, new and/or untested environment (common differences are things like weather/temperature/altitude), for when you don't have the chrono, ideal range, and/or glass needed to even spot it.
LIke has been mentioned, BC changes with different MV, so without retesting for the new environment/conditions, truing is it.
You want to true MV as close to Mach 1.2 as you can.
You can get a CDM or Custom Drag Model by using anything with our Elite Engine in it. That can be a Kestrel, Garmin, Vortex, Bushnell, Wilcox, L3, AB Mobile App.... etc. As long as it has the Elite Engine or better.
They did cover this topic on miles to matches. I think the science of accuracy is the one I’m specifically talking about. That sounds like a nice range. I wish I had access to a range where I could go down range, so I could do an actual water line test. I’ve always been somewhat rushed when verifying dope, at least with the opportunities I’ve had at long distance. What I mean by that is if I was able to get a couple 2 or 3 impacts on the 1000yd plate, didn’t matter wear they impacted, I’d call it good. With factory ammunition and the amount of vertical dispersion, I can’t really fine tune it. I can get it close enough for my abilities with my ammo to get me by.
AFAIK, as a practical matter, doing this by the book is harder than when mach 1.2 was well inside 1,000 yards because they OGs were shooting a 308...Its not that bad, again in theory, since you can use the Ballistics software to get your mach 1.2 distance for your load MV. The main problem is transonic ranges are now very often beyond 1,000 yds, more like 1,100 or 1,200yds. Most people don't have reliable access to ranges of this distance, since most people are lucky to get a 1,000 yds range in reasonable distance. Also, when you are out that far, its harder to get dead-calm conditions for testing stuff at .1 click precision. Likewise, its harder to setup and shoot paper etc. since most paper disciplines like BR and Fclass are 1K max. Somebody please correct me if I'm wrong, but I think the crux of the matter here is practicality. YMMV.
Yeah, having the right location/distance needed, and the acceptable ES/SD numbers from either being your own ammo factory (reloading) or buying multiple cases from the same lot number (the only way when shooting factory stuff IMHO), and of course, time to really see what one's waterline looks like downrange, is sort of key to honing in on one's legit average BC.
That said, having a solid chrono-tested average MV on record and a solid zero on one's gun, along with a known distance target in the 500-600 yard range, can go a long way when one incorporates a properly set up App's modern truing features. When all of that is working, really all one needs is ~700ish yards IMO.
Several times I've chrono'd and then shot out to 1250 yards only to find out that I should/could have believed what the impacts at 600 and 750 along with the App/calculator (Strelok Pro in my case), were telling me.
Amusingly enough, with the 109 eldm, going 2860fps, 27"hg+/-, 35%humidity; I run a .299 g7. Enough to keep me within .1 mil+/- at 1017yds. Jury is still out on the reliabilty of this projectile holding .2 mil at that range.
Aside from that, a good chrono goes along way to getting 1 variable removed. The custom drag models from AB are badass, the farther out you run. As stated before, the varying BC as the bullet flies can be a pickle.
Aside from that, a good chrono goes along way to getting 1 variable removed. The custom drag models from AB are badass, the farther out you run. As stated before, the varying BC as the bullet flies can be a pickle.
So I shot the mile this weekend for the first time. Leading up to Sunday I shot every week getting data; weather, chrono and all. This is all at sea level. Finally the day comes and I drive 2.5 hours. Fot the last 6 weeks temps been in the mid to high 90's but sunday its 71! I sinc my kestrel and take 10 shots out to 1000 true my data then im off to shoot the mile. 1760 exactly. Then I true this also in AB. it drops my MV 120 fps. Is this right? or possible? I went from sea level to 470 ft. and 20 degree tempature change. I just feel confused.
You want to true you MV before your bullet goes transonic (1340ish fps). The kestrel will show you the recommend range to true in the cal MV screen. Then you can do a cal DSF for truing data past transonic. The cal DSF will only change your trajectory past transonic it won't change your drops inside supersonic. I'd recommend using AB custom drag curves over a G1 or G7 BC.
So 1330fps is what AB is saying for 1000 yards. The truing worked. It gave me great data and I hit the mile. Just crazy thinking the MV would drop. Could the BC need to change? Or does it matter as long as the data correction given is the right dope?
If your real world data matches the Kestrel, then your good to go. But i would confirm your data on another day just to make sure. What chronograph are you using? What gun powder? Were you chroning while shooting? The AB CDM's are always spot on for me, no need to mess with BC.
I am planning to check everything out another time soon. I just don't have regular access to anything past 100 yards at the moment. I'm using a magnetospeed sporter but didnt shoot with it on that day. Precision One factory 6.5 140 gr eld Match. I think next time I'll shoot with it on. I'm new to the CDMs anywhere to get more info on them?
You can buy them in the APP or the Elite Kestrel 5700 comes with the whole library. Just pick your bullet and pick custom curve instead of G1 or G7. I would at least chrono a few rounds to get a baseline for your current temperature.
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