Dial Drop Determination Questions?

[Bird Dog]

I know this has been asked before.... how are you determining the true B.C. of your loads which would impact the dial setting? I know many manufacturers tend to over estimate the published B.C. by as much as 10% which can cause quite a difference at even 600yrds for an impact and energy. Factory ammunition is historically very different in each gun for velocity.

 

Also, what do you use for the elevation and temperature? I know many members shoot on hot and cold to basically average the two.

 

I thought I had seen a basic 5000 ft @ 70 degrees F working very well for most.

 

What is the common thought on the leupold dial systems that are custom to your load and bullet weight? It seems like a nice idea but could be off at further ranges just with temperature and elevation? Not to mention the temperature impacts on the ammo itself with velocity?

[rcdinaz]

I set my drops using the shooter app and base them on my shooting results at 100yds and then adjusted for my POI at 500yds and sometimes 700 yds. The app wil fine tune the MV so that the drop model fits your results. 500 and in it does not make too much difference, past that it does.

 

I do not have any of the load specific turrets but will get a few initially for my Mark IV. My plan is to start using the stick on ones from custom turret before I finalize anything.

 

I also agree that 5000 ft is a good middle ground and when I discussed it with the turret guys the rule of thumb was POI was pretty good up and down about 1500 ft in most cases. So that would cover you for almost all of our hunting out to about 500yds depending on how your gun is set up. You could do a 200yd zero and stretch it a bit.

[Becker]

I stick with the basic MOA hatch marks on my turrets simply for the reasons mentioned above (Temps and Elevation changes). Its easy enough to print out reference cards based on the situations you will be hunting in and adapt. Or simply having the G7 range finder It really depends on how far you want to shoot and how many places you plan to take the gun to hunt. A custom turret WILL limit you if thats all you plan to use. EG theres a deer at 523 yards, dial up the scope and shoot. If you are up on calculating all the factors you should be able to compensate.

 

It seems to me that you are wanting to put together a ballistics profile for your gun??? I don't know you and don't want to insult you in anyway so if you already know everything I am going to type here I apologize but here is my 2 cents.

 

If you are serious about your guns ballistics I would recommend one tool to buy. A good Kestrel!!! It will measure your wind speeds, elevation, temperature, barometric pressure. Everything you will need to get the exact ballistics profile put together for your gun.

 

As far as determining your basic factors (muzzle velocities, etc. for drop compensation) I find it best to back calculate. Like you said there is lots of info out there but knowing what exactly your gun is doing is best. The easiest way I know to do that without having all the fancy chronographs and what not is to simply zero your gun at your desired distance (100,200,or 300) then go shoot the farthest distance possible (800 to 1000 yards). Figure out your drop. With turrets its fairly easy, you can get really close with available information and then really dial in for your gun for that long distance. Then use any basic ballistics program and make it match what your gun is shooting because you NOW KNOW what the gun does. Back calculating ALWAYS provides more accurate results. I think you'll be surprised at the difference of say zeroing then shooting 500 yards, then extrapolating that to 1000 vs back calculating everything from that 1000 yards.

 

When using the ballistics program use the real time information from when you were shooting (from your KESTREL). The temps when you were shooting and elevation etc. All that is easy to do. Once you get the info all dialed in you should have an exact profile for your gun. Then you can mess around with the temp and elevation settings on the program and watch what happens. If you are really into having that custom turret you should be able to use the program now and figure out what the best average would be for your desired hunting situations!

[308Nut]

I use the double chronograph method. It takes a bit of time to get set up accurately. I set them exactly 600' apart. Document the ambient air temp, pressure and humidity and make notes of the near and far velocities. Then you can compare the averages with JBM or other shooting apps. You basically adjust your BC until the near and far velocities match. This isn't the best method for 1k shooting and beyond but is scary accurate to 700 yards and it'll get you real close at 1k. Then you can adjust as needed from drop tests. You'll know really quick if you're doing something wrong if your drops based on your calculated BC don't match your app. Best to get those ironed out before you settle on the final BC from chrony and drop tests.

 

Drop tests alone aren't always conclusive because it only takes minor mistakes to generate either an over or under estimate. Near and far velocities are bullet proof assuming your chronographs are accurate. Then if your dials don't match, either you're doing something wrong or your scope dials aren't precise or both but at least you'll have a clearer idea of your down range impact velocity.

 

Berger bullets does a pretty good job of getting their BCs pretty close. Sierra also does a great job for most of their bullets as does hornady. Hornady doesn't test them over as many velocity ranges as the other 2 but out to 600-700 hornady numbers will be very close. Nosler has always been a bit on the high side but with their new ABLR they're WAY on the high side. At least with the 210 thirty cal. Berger bases their G1 BCs on an average where Sierra gives you multiple G1 BC values over several velocity ranges since BC changes with velocity. Use of the G7 model cuts down on the sensitivity but like every thing else, isn't fool proof.

 

In short, you have to get an accurate distance between chronies and you have to have atmospheric data that is spot on to make it work right.

 

I have compared my tests against other known, trusted sources and have been less than 1% off almost every time. Less than 2% the other times. Usually .5%.

[STOMP442]

The best way to determine drops and turret values is by shooting and lots of it. Practice at the ranges you intend to shoot and practice in adverse conditions and varying elevations to better understand what you and your rifle are doing. Ballistic calculators are great but they are only as good as the information input into them. I will never trust a calculator over my proven data and drop charts developed at the range and in the field.

 

As far as B.C.s go berger has the most accurate and scientific data available of any bullet manufacturer. They use multiple chronographs acoustic sensors and radar over 600 yards to determine actual bcs of their bullets. They also use the G7 standard which is a much more consistent drag model for todays modern bullet designs. The actual bc can have slight changes depending on elevation and weather conditions but for the most part are very consistent. Sierra also provides very good information but does so using the G1 standard models which is velocity dependent. Hornady I will admit has come along way in their BC information especially in thier Amax and Match bullet lines but can at times be a little exaggerated but not by much and depending on the bullet. Nosler just likes to blow smoke and lots of it, their ballistic testing is limited to 100 yards and pushed at the highest velocities possible which doesnt amount to good data at all for the average hunter / shooter.

 

My opinion on a custom dial system vs the standard moa knob is this. If you changes bullets or loads at anytime your custom dial is pretty much useless and you will have to spend the money on a new one. The moa knob allows you the freedom to change at any time or for any situation by simply making a new drop chart. Its just as easy to dial up moa as it is to dial up to a yardage on a turret.

[willhunt4coues]

You can call any manufacturer and ask them what the G7 is of your bullet. The G7 profile is based off a sharp nose and boat tail when the G1 is based off a sharp nose and flat base. You can use the G1 but you will only get close. The G7 profile is the best to use for any long range solutions. Most companies still use the G1 profile because of the point that the G1 is a higher number. The reason why they did this is because if the customer. When you go buy bullets you are looking for the bigger number. If they used the CORRECT profile G7 then that number is a lot lower making you believe that the bullet is no good. My G7 on berger 6.5 140gn is .313 and the G1 is .612. I shoot long range a lot and would NEVER go to a ballistics turret because of the simple fact that conditions are always changing. Like others have said get you a Kestral and a ballistics app for your phone and you will be set. Google is your friend. Learning is even more fun. Get on Google and look up the difference between the G1 standard and the G7 standard. Also look up what others are using for long range (ie ballistics turrets, standard moa turrets, or standard mil turrets) you will be surprised. Its a lot of math involved but even more fun when you get out and enter everything that you can and hit a target with 1 shot at 1000+ yards.

 

Applied ballistics is another dvd, book, app that you can look into. They will tell you how to obtain your BC by shooting 3 different distances. They will also explain into detail what your hit percentage is at different ranges and wind age. What do you have to lose. Have fun and be safe.

[Bird Dog]

Thanks guys. This is exactly what I though would be. Practice......... it is a shame how many people won't/don't practice to make the proper determinations needed.

[AxisWorks LLC]

Trajectory is trajectory. Inputting B.C. weight and velocity is only a reference point to get you close. Assuming you have done the work and have developed a precision load the next step is "trajectory validation" In a nut shell it doesn't matter if you have the exact B.C. or velocity or weight of your projectile. You shoot the trajectory and adjust velocity to replicate it with your calculations. This video should help explain how to accomplish this.

 

[308Nut]

An accurate BC is needed for a long range hunter. They need to know how much impact velocity there is for two reasons. Energy and expansion. All hunting bullets have a minimum velocity expansion threshold. We need to know what them minimum is and what our impact velocity will be so we can draw a line or close to it as to whether or not a shot is within our rifles capability even if it is within our shooting capability.

[AxisWorks LLC]

An accurate BC is needed for a long range hunter. They need to know how much impact velocity there is for two reasons. Energy and expansion. All hunting bullets have a minimum velocity expansion threshold. We need to know what them minimum is and what our impact velocity will be so we can draw a line or close to it as to whether or not a shot is within our rifles capability even if it is within our shooting capability.

 

I totally agree with you but now we have switched gears into terminal ballistics. Assuming the OP is using this for a hunting situation 308Nut's reply is spot on in determining your exact effective range.

Personally I have never gone into this amount of detail to figure out my exact down to the yardage termanal balistics. Even though knowing the manufacturers published B.C. isnt exact I've used it to calculate efective termanal balistics and never "push the evelope" staying within 100yds or so of that range. I find this very interesting and plan on exploring it more.