When truing MV at what yard marker do you start truing BC? and is that yard marker different for different calibers?
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Truing MV vs. BC
- Thread starter Ppierceall
- Start date
D
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Most true velocity at 500 yards, because out to 500 yards, velocity is the main component of drop. Provided your BC is somewhere in the immediate neighborhood, you will be fine.
Most rounds start to really fall off the table, so to speak, somewhere between 700-800 yards. If you true your BC somewhere in this range to match actual observed drops, it will be accurate to 1000 yards.
If it is not, then there are likely other issues at play, such as scope tracking etc...
Most rounds start to really fall off the table, so to speak, somewhere between 700-800 yards. If you true your BC somewhere in this range to match actual observed drops, it will be accurate to 1000 yards.
If it is not, then there are likely other issues at play, such as scope tracking etc...
You want to test for MV Truing at Mach 1.2 +/-.
D
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Let's keep it simple for the new guys Doc. Mach 1.2 for a round like I shoot in my Winmag is 1200 yards. No noob is going to shoot paper at 1200 yards and get anything useful out of it.
I use Strelok, but I believe my process would work with most any ballistic calcultor:
1. Confirm zero.
2. Check velocity over at least a 10 shot string with magneto speed.
3. Shoot out to where the bullet velocity is approximately 1,400 FPS. For me this was 1,300 yards. This is also the farthest I plan to shoot at targets.
4. True B.C. only to make the drop at 1,300 yards match my calculator.
After doing this I have shot at every distance from 100 to 1,300 yards and my drop has been within .1 mils always. This has been for the last 800 rounds on my barrel and at different altitudes and barometric pressures. I have done this with different rifles and cartridges now and it works consistently well. I am not shooting at distances beyond supersonic so if you are doing that you might want to modify this method. Also, every other variable in my calculator is checked and is spot on.
1. Confirm zero.
2. Check velocity over at least a 10 shot string with magneto speed.
3. Shoot out to where the bullet velocity is approximately 1,400 FPS. For me this was 1,300 yards. This is also the farthest I plan to shoot at targets.
4. True B.C. only to make the drop at 1,300 yards match my calculator.
After doing this I have shot at every distance from 100 to 1,300 yards and my drop has been within .1 mils always. This has been for the last 800 rounds on my barrel and at different altitudes and barometric pressures. I have done this with different rifles and cartridges now and it works consistently well. I am not shooting at distances beyond supersonic so if you are doing that you might want to modify this method. Also, every other variable in my calculator is checked and is spot on.
Let’s keep it simple for the noobs. I don’t care if you are shooting 1 yard or 1000 if your MV is different in any way than what the manufacturer (or litz or whomever) used when calculating their BC, your BC is wrong. Period. If you know your MV because you used a chrono (and if you don’t use a chrono everything is a SWAG anyway so your method is as good as any) why would you true it? It’s already true because your chrono told you. Yeah yeah. margin of error and accuracy percentages and such. Ok I get that. But if I’m shooting a prime 130 OTM 6.5 CM at 2950 and the manufacturer says a BC of x at 2770, my BC is higher with my known MV. The unknown is BC so why would I not true that? Then at distance like DOC said right at transonic tweak your MV, I’ve never had to adjust by more than 20 FPS. You don’t need paper. A water mark on a steel plate will suffice (yes not all of us are this fortunate).
I true BC at 1200 yards or so, borderline transonic. If you can see where the bullet hit relative to your point of aim, you can use that to true, it doesn't need to be paper. I use a magnetospeed to get velocity and I trust that number. Everything inside 800 yards is always solid. You don't really see the deviation until farther out.
One other thing to keep in mind is that BC can be different even from barrel to barrel, I've shot the same lot of bullets, at the same speed, out of two different barrels (same twist) and observed different BC's. The barrel can compress the bullet shape slightly depending on bore diameter and affect the form factor and how the bullet flies.
One other thing to keep in mind is that BC can be different even from barrel to barrel, I've shot the same lot of bullets, at the same speed, out of two different barrels (same twist) and observed different BC's. The barrel can compress the bullet shape slightly depending on bore diameter and affect the form factor and how the bullet flies.
Frank stated the same thing on a recent podcast. The BC provided by the manufacturer is really only valid from their rifle. However this begs a dumb question, if you have known MV data from a quality chronograph, why not just true the BC even at shorter ranges like @TacticalDillhole mentioned? Or are you saying that if the MV is good the different BC wouldn't result in errors that are drastic at close range?
Guess that’s a personal choice. Do you want to be accuarate and precise or just accurate.
The former.
I'm asking because I don't understand. Your way seems the right way to go. However, do I take that as you never tweak velocity if you have accurately measured MVs?
D
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Real simple concept. True velocity at 500 yards, and adjust BC at two longer distances. Then your dope is correct at all distances from the muzzle on out.
True velocity and BC at extended ranges only, and you will be off at the closer distances.
Unless your shooting an extremely high BC bullet very fast, There is no one number that will get you from the muzzle to 1500+ yards.
Most people starting out just want to be accurate at all ranges to 1K yards. They ask a simple question and the peanut gallery goes all ELR on thier ass.
True velocity and BC at extended ranges only, and you will be off at the closer distances.
Unless your shooting an extremely high BC bullet very fast, There is no one number that will get you from the muzzle to 1500+ yards.
Most people starting out just want to be accurate at all ranges to 1K yards. They ask a simple question and the peanut gallery goes all ELR on thier ass.
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No I do tweak it but just ever so slightly. My rule of thumb is no more than half of my SD.
But I don’t do it till I have done the BC work. The MV tweak is done at distance as close to transonic as well. It’s necessary sometimes just to get that final bit of refinement. But because I do use a chrono (many times 2 at the same time with a lab and MS) I’m not trying to true what I know what isn’t lying.
IF you have a chrono, you dont need to true your velocity, just true your BC at 800+ yards.
D
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Velocity is the main element in trajectory at 500 yards and closer. You don't have to believe me, run the numbers yourself. See how much a 50fps difference makes at 500, and then tweak your BC to get the same change and see how much it takes. Chrono's are better than they have ever been but they are not perfect.
Secondly, truing BC and velocity out at 800 yards and further introduces a multitude of variables that can really mess up your data. You might get it right, but there is an even chance you'll fuck it up somehow. This is evidenced by all the people popping up on this very forum wanting to get unfucked after they've tried it the hard way.
Thirdly, there is a reason that Sierra has been doing banded BC's for a few decades or so. With super dooper magnums the first band is usually 2500+fps. Guess what, that roughly equates to 500 yards. The next band usually extends down to 1900-2000fps. Guess what, that roughly equates to 800 yards. The next band usually is down to 1600fps, which neatly equates to about 1200 yards.
There is no need to reinvent the wheel. None of this shit is new anyway.
The first number is usually 2800fps up, the second is 2000 to 2800 and then it's 1800 and below for most I have seen with Sierra
I think 800 is the right balance to true most of what we shoot, I have not seen it negatively affect the solutions and the MV adjustment is much, much smaller when doing the BC here. Averaging the BC at 800 and then truing the MV using my Kestrel resulted in a 28fps change vs what is normally well over 50fps in some cases even 100fps.
Hornady is using around 800 yards for their average since getting Doppler vs most people use 300 yards which is industry standard. Although they now offer it in bands as well in various machs
The 300 yard average is safe, but I think for most of us, 800 is better.
I think 800 is the right balance to true most of what we shoot, I have not seen it negatively affect the solutions and the MV adjustment is much, much smaller when doing the BC here. Averaging the BC at 800 and then truing the MV using my Kestrel resulted in a 28fps change vs what is normally well over 50fps in some cases even 100fps.
Hornady is using around 800 yards for their average since getting Doppler vs most people use 300 yards which is industry standard. Although they now offer it in bands as well in various machs
The 300 yard average is safe, but I think for most of us, 800 is better.
Appreciate the feedback.
So in a sense...
- You measure MV with your chrono
- True the drop via adjustment of BC
- tweak MV by no more than half of SD value.
I have had a kestrel 5700 now for two weeks - I had been using Geo Ballistics before that for a few years. I was at a competition this past week and a pro shooter showed me this method. Good to have conformation and to see how others do it as well. The you tube videos just show how to use the Cal MV on the kestrel.
Good thread. So, looking at Sierra's data for the 11O SMK:
.617 2600 fps and above
.605 between 1900 and 2600
.580 1900 fps and below
According to Sierra , the bc remains constant within a 700 fps "zone". Safe to assume the same between 2600 and 3000? Only 400 fps difference there, but I wonder what the curve is as you move up in speed? I always see about a .2 MIL difference in solution from my Kilo and my Kestrel, which is weird because I think they both have the AB solver.
.617 2600 fps and above
.605 between 1900 and 2600
.580 1900 fps and below
According to Sierra , the bc remains constant within a 700 fps "zone". Safe to assume the same between 2600 and 3000? Only 400 fps difference there, but I wonder what the curve is as you move up in speed? I always see about a .2 MIL difference in solution from my Kilo and my Kestrel, which is weird because I think they both have the AB solver.
just for more confirmation, there are tons of top shooters who do this method...pretty much everyone of them i know and have had convos with about it, does similar
You bet! The Champ taught me to do it that way, and it's worked great for me.
D
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The BC does not remain constant, from any rifle, ever. What all of these BC banding programs do is break up the flight into segments and give corrections to keep things true. It's like the corrections you make to the steering wheel while driving down the road. The corrections are small enough and frequent enough to give the appearance of driving straight. Same thing here, some bullets need more frequent correction than others and at different speeds.
I can't speak to the difference in your solvers, other than to say go back and double check that every single input is identical. I have AB and 4DOF on my phone, but find myself using Strelok Pro and it's multi-BC function more and more. It isn't as sophisticated maybe, as the others, but I can see every single input. Nothing is "grabbed, populated, transmitted, blue toothed" for me.
With room for 5 BC inputs, I can correct the curve to match actual drop waaaaaaay out there. I'm only using 3 BC's to get my 338AX to 2500 yards, and it is accurate from the muzzle to steel. The user interface is way better also. Everything you want to see is either shown on the home screen or accessible from the home screen. Navigating AB and 4DOF just pisses me off.
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Why do you care if your calculator matches the real world performance? I don't get the obsession with trying to make what the solver says agree with the impacts. To what end does your solver need to match down range performance?
Is this not why we gather and record DOPE? To me a ballistic computer is ONLY to get me in the neighborhood. It's not to actually compute firing solutions when it counts. I want to know those long before I ever get into positon, and I don't want to have to refer to something with a battery to do it.
You could waste all your time trying to tweak the solver to match, when you could be shooting, gathering more DOPE, and confirming exactly how the rifle behaves in those conditions. At some point you have so much data in so many different conditions there's no need to ever refer to a solver! Right about then your barrel shoots out and your precision goes to hell, and you can't hit shit...
Is this not why we gather and record DOPE? To me a ballistic computer is ONLY to get me in the neighborhood. It's not to actually compute firing solutions when it counts. I want to know those long before I ever get into positon, and I don't want to have to refer to something with a battery to do it.
You could waste all your time trying to tweak the solver to match, when you could be shooting, gathering more DOPE, and confirming exactly how the rifle behaves in those conditions. At some point you have so much data in so many different conditions there's no need to ever refer to a solver! Right about then your barrel shoots out and your precision goes to hell, and you can't hit shit...
I only care to the point where it gets me in the neighborhood. I just stated I thought it was odd they were off. When I shoot in a match, I use a dope card made to the best of my ability right before the match happens if I have time. As conditions change I make adjustments on the fly to my elevation if I need to. Honestly though, most of the targets are not so small that if I am off a tenth or so at 700-800 yards I won't notice a difference. If I have to shoot a bunch of targets in a short period of time I don't really analyze where my bullet hits on the target all the time. I do take note if I notice a pattern developing (always high, low, etc) however.
I do rely a little more on the Kilo when hunting, because I don't have the luxury of gathering dope for the various elevations, environmental conditions, etc. Off topic, but I actually started shooting long range in hunting applications and sort of moved into doing the field practical type matches as something to do. I find myself way more hyper aware of the shooting conditions now when hunting. So much can go wrong on longer shots on animals I usually end up either not shooting at all or narrowing my margin of error by getting as close as I can if conditions allow.
it doesnt take long to tweak a solver if you know what youre doing...gathering dope is well and good IF you get that chance, its not always an option...some of us shoot a bunch of different caliber/bullet combos in a bunch of different locations
The same data you gathered the first time is used to true the software and then the software will manage changes in conditions and locations without having to shoot more.
It's not one or the other, it's both, you shoot your rifle, gather real world data then retire to your home and true the software, without shooting it. The data collected is fed into the computer along with the conditions of the Day YOUR DOPE as you put it. Once trued the software works and helps manage changes you cannot understand from your one location or range.
If i am in Colorado, and I am going to Shoot Core in FLA the conditions are completely different, 5000ft ASL with an average DA of 8000FT, then in Core it might be 300ft ASL with an Average DA of 2500ft. For me it usually results in a .5 mil difference at 800 yards. The software helps manage this without guessing or need to arrive early to shoot.
I shot the SHTC in Colville WA, another area that varies from here in CO. Properly trued software manages this change. No extra work on the range, no burning out barrels, no extra shooting involved you still gather you DOPE but you apply it to the software. No distractions, no issues if you do it right. I don't even need my computer on the range with me when gathering the data, just this data sheet,
I even created a datebook page through Impact Databooks to manage this
I get that, and I do pull it out and check the difference to my dope at a given adjusted pressure/altitude, but I usually have those pre-printed. I do bring a solver when I shoot. I just hardly refer to it unless I don't have that pressure figured, and I almost always do. I normally oscillate in what must seem a pretty narrow range for a traveling sniper. I can't remember the last time I actually used it, but then I'm not shooting ELR, or working where I have to get an impact on the cold bore. I tend to have good dope in the conditions I shoot and compete under. I also show up early and check zero/foul.
So am I to interpret this as you enter your chrono velocity and listed bc into your solver. Shoot it at 500 and tweak your velocity to get correct impacts. Then take it out to 800-1000, and tweak your bc to get correct impacts there?
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I wonder how much better that method would work if it wasn't just flat out WRONG!!!
I love it when a guy throws a grenade in a room but doesn’t offer any alternative insight.
I'm joking 
I know Mr. Skookum personally, and thought I'd take a moment to get him spun up.
Adjusting velcity to true your trajectory at closer range and adjusting bc to true it up at longer ranges is exactly what I do as well.
It works well enough that Mr. Skookum, while spotting for me, got me and my Creedmoor on target @ a mile with just a few rounds.
I know Mr. Skookum personally, and thought I'd take a moment to get him spun up.
Adjusting velcity to true your trajectory at closer range and adjusting bc to true it up at longer ranges is exactly what I do as well.
It works well enough that Mr. Skookum, while spotting for me, got me and my Creedmoor on target @ a mile with just a few rounds.
Ah ok. I’m all for heckling.I'm joking
I know Mr. Skookum personally, and thought I'd take a moment to get him spun up.
Adjusting velcity to true your trajectory at closer range and adjusting bc to true it up at longer ranges is exactly what I do as well.
It works well enough that Mr. Skookum, while spotting for me, got me and my Creedmoor on target @ a mile with just a few rounds.
D
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If I recall correctly, it was the first round wasn't it?I'm joking
I know Mr. Skookum personally, and thought I'd take a moment to get him spun up.
Adjusting velcity to true your trajectory at closer range and adjusting bc to true it up at longer ranges is exactly what I do as well.
It works well enough that Mr. Skookum, while spotting for me, got me and my Creedmoor on target @ a mile with just a few rounds.
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Along the same line of thought, I kinda learned to do that as a rule, through experimentation.
Years ago I shot Tiger Valleys 5 day level 2 rifle course. Early in the course we used a 1000yd known distance range and shot groups for dope at each distance line, 100 yard increments.
After I got back to my hotel room that first evening, I started plugging my downrange feedback info into g7s ballistic program trying to get the softwares predictive trajectory curve to match my actual trajectory. I obviously wanted the software to show a curve that actually tracked the same curve I shot that day. Or at least, at each 100 yard increment.
By adjusting either the MV or the BC individually, I could only ever get the softwares trajectory to match the actual trajector, at 1 distance. I could play with the MV or BC and get the curves to intersect at any distance I wanted, but couldn't get them to concurrently match at all the distances.
The only thing that worked to both shape the trajectory curve and match it's graphed location at each distance was to change both.
Changing the velocity increased/decreased the radius of the curve at the closer ranges, and changing the Bc changed the shape of the curve at its more parabolic end.
Years ago I shot Tiger Valleys 5 day level 2 rifle course. Early in the course we used a 1000yd known distance range and shot groups for dope at each distance line, 100 yard increments.
After I got back to my hotel room that first evening, I started plugging my downrange feedback info into g7s ballistic program trying to get the softwares predictive trajectory curve to match my actual trajectory. I obviously wanted the software to show a curve that actually tracked the same curve I shot that day. Or at least, at each 100 yard increment.
By adjusting either the MV or the BC individually, I could only ever get the softwares trajectory to match the actual trajector, at 1 distance. I could play with the MV or BC and get the curves to intersect at any distance I wanted, but couldn't get them to concurrently match at all the distances.
The only thing that worked to both shape the trajectory curve and match it's graphed location at each distance was to change both.
Changing the velocity increased/decreased the radius of the curve at the closer ranges, and changing the Bc changed the shape of the curve at its more parabolic end.
So I actually had an opportunity to try this today. The weather today in New England was hot and humid...very oppressive conditions in direct sunlight.
Zero conditions (Previous-2 weeks ago)
Zero range =201 yards
BH=2.08 inches
ZO=0.15 inches
ZH=0.2 inches
Temp=66
RH=44%
SP=30.01
Today's environmental
Temp=92
RH=71%
SP=29.84
Wind 2mph from 8 O'Clock
Shooting Hornady match 140 Grain ELDM. Used the AB Ballistics CDM instead of G1 or G7 values since i just upgraded my Kestrel to the full AB (Elite) status. My buddy had his Magnetospeed and we fired a string of 5 rounds.
Average MV=2710. ES=34 (High was 2728 and low was 2694).
I entered 2710 into the Kestrel. Coriolis and SD are off. WS1 was 0 mph and WD was 12 O'Clock to turn off AJ. I measured the distance to target using my LRF and it was 501 yards. Kestrel called out 2.3 mils up. This was close to my usual 2.4 mil correction so I figured 2.3 was right since temp was a lot warmer. Fired 2 shots at the 6" plate (Dead Center POA) and my spotter called miss and very high. Adjusted 0.1 mil to 2.2 and fired again and outcome was the same. I ended up adjusting to 2 mils and was getting POI exact to POA. WTF?? Ran the MV calibrate function on the Kestrel and it calibrated MV to 2891 fps against a just measured average of 2710....WTF??? However, the bullets don't lie and I was making repeated first shot hits on the 4"plates with this setting.
At 300 yards, the Kestrel called out 0.5 mils up with the corrected MV used at 500 yards, and the actual was 0.3 mils. So the corrected 500 yard MV didn't work at 300 yards.
Any pointers???
Two questions
1. Do you have the MV temp table filled out?
2. Why are you using a 200yd zero in a 6.5?
D
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Your data isn't valid because you didn't reconfirm your zero. Something as simple as a different lighting condition could have caused that much difference.
As TD said, the idea is to start with a 100 yard zero when gathering data.
No.
I was 0.3 mils off at 500 (2.0 mils actual versus 2.3 predicted). Corrected velocity so that the Kestrel agreed with true POI at 500 (2 mils). Then I moved to 300. Kestrel was 0.2 mils off at 300 even though I was using the “corrected” velocity from 500 yards
No I don’t have DOPE as a function of temperature
I always zero at 200 just habit
The difference was less as I pointed out in my last post.
I have always zeroed at 200 and never had a problem but I can zero at 100 and try it again. However, you reconfirm zero every time you shoot?
I do because it’s easy at my range. But if my actual vs predicted wasn’t lining up and I know my data is good, that’s the first thing I’d check after making sure my rings were secure
I checked the scope while there using my Borka and it was exact. Scope isn’t the issue. I should have checked zero but I was lazy. The one thing I thought about was mirage. It was super hot and the mirage was strong but nearly vertical. Wonder if my POA was really where I thought it was.
Wanted to share my experience;
After listening to Frank and Mike on pocasts about wind and the Kestrel I had the opportunity to work with the info from both pocasts. ...This past week I began work with a new sig 2400. I used the custom drag curve and a good speed from 4 five shot chrono sessions over the course of two weeks . I set wind to zero mph and zero degrees. Dope was spot on from 550 out to 1200 yards. I wanted to true my kestrel 4500 to match the dope from the 2400. I did not change muzle velocity, I changed the G1 BC from .43 to .46. My kestrel and Sig now match each other and real world dope from 550 to 1200. It will be interesting to shoot in changing conditions and locations to see if they continue to track with each other and actual dope.
After listening to all the conversations on this topic and investing time and money to get solid velocity/temp data from a labradar it seemed counter productive to change that number. Removing all wind from the calculation seems to have allowed me ton only focus on effects of gravity on the trajectory. I trued bac at 800 yards for the kestrel and it then lined up all the way out to 1200.
Elevation was 5600ft, barometer 24.8, 6.5 CM 107smk at 3097fps. Printed G1bc is .430, trued is .460
I have limited experience compared to many on here. Trueing BC seems to have worked for me. Time will confirm this ....or not.
After listening to Frank and Mike on pocasts about wind and the Kestrel I had the opportunity to work with the info from both pocasts. ...This past week I began work with a new sig 2400. I used the custom drag curve and a good speed from 4 five shot chrono sessions over the course of two weeks . I set wind to zero mph and zero degrees. Dope was spot on from 550 out to 1200 yards. I wanted to true my kestrel 4500 to match the dope from the 2400. I did not change muzle velocity, I changed the G1 BC from .43 to .46. My kestrel and Sig now match each other and real world dope from 550 to 1200. It will be interesting to shoot in changing conditions and locations to see if they continue to track with each other and actual dope.
After listening to all the conversations on this topic and investing time and money to get solid velocity/temp data from a labradar it seemed counter productive to change that number. Removing all wind from the calculation seems to have allowed me ton only focus on effects of gravity on the trajectory. I trued bac at 800 yards for the kestrel and it then lined up all the way out to 1200.
Elevation was 5600ft, barometer 24.8, 6.5 CM 107smk at 3097fps. Printed G1bc is .430, trued is .460
I have limited experience compared to many on here. Trueing BC seems to have worked for me. Time will confirm this ....or not.
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2710 does seem very slow for a 6.5 at 92 degrees. I get 2788 at 88 with the 140’s.
I would definitely just start from scratch with your zero. Make sure you get an accurate MV and go from there. Don’t use the CDM and stick with G1.
D
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I misread your post initially so I deleted this post. Please ignore it. I answered you again in another post.
D
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You reconfirm zero whenever you are making changes or determining your base data. You have to have a solid known starting point before you do anything else.
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I thought so as well because the stated MV on the box is 2710 which is the average that I measured at 92 degrees. The bullets were also out in the direct sunlight as there is no cover so the internal temp in the case could be even higher.
I doubt that Hornady makes their measurements at hot temperature.
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