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I am trying to figure out how to calculate the MPBR for popular calibers such as the .270 win (130 grains), .243 win (100 grains), .308 win (150 grains) and 30/06 (150 grains), for common factory loads, using the information given in standard ballistic charts. I am thinking about a small deer as a target (i.e. 15 inches from back to brisket). Thus, I think that the bullet shouldn’t rise more than 3 inches before starting to drop.
 

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Discussion Starter #3
Thanks for the suggestion. The only thing difficult to determine is the drag: G1, G2,…G8. I understand this has to do with the bullet shape and dimensions, but there is no pattern or chart to base from.
 

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E.O.,

The velocity tables published are not usually high precision. The manufacturer typically just takes a G1 ballistic coefficient for his bullet and uses that to calculate the drops in velocity and vertical trajectory for his charts and tables. The tables don't contain measured values. So if you want to match what they got, just use the G1 function. Moreover, point blank range is normally short enough that your result won't change it more than a yard switching between drag functions appropriate for the shape of the bullet. It's at very long ranges that drop differences due to the differences in drag function become an issue. MPBR will be under 300 yards in most instances, even with a 6" circle defining a point blank hit zone. Too short for a practical difference to appear.

For example, I looked at Winchester's 150 grain Ballistic Silvertip ammunition. It claims a muzzle velocity of 2810 fps. The table says the velocity at 500 yards is 1856 fps. When I put those two velocities and that spacing into this calculator and select the G1 drag function, I get a G1 BC of 0.442. If I then plot a trajectory table using that single G1 BC and 2810 fps for MV, the velocities I get for 100, 200, 300, and 400 yards all match Winchester's table perfectly, which is how I know that the table was calculated and not measured. Because the G1 BC decreases with velocity for a boattail spitzer nose bullet, a measured velocity would be a few fps lower at 500 yards.

If I then put that 0.442 BC and muzzle velocity and bullet diameter and 150 grain bullet weight into this other calculator and ask it to convert to the G7 BC, knowing that will match the shape of the bullet better, I get a G7 BC of 0.221. Knowing the G7 is actually for a secant ogive BT, I also get a G5 BC of 0.274, which is for a shorter boattail tangent ogive shape. The actual bullet will likely fall between the G5 and G7 somewhere in its real behavior.

What's the difference? At 300 yards, not much. The G1 gives 2211 fps at 300 yards, the G7 gives 2208 fps, the G5 gives 2196 fps. The G1 says the transit time will be 0.3613 seconds, the G7 says 0.3615 seconds, and the G5 says 0.3621 seconds. That's equivalent to 1.4 fps difference in average velocity between the G1 and G7 drag function velocity predictions, and 4 fps difference between the G1 and G5. Both differences are smaller than actual shot-to-shot variation is likely to be.

The difference between the Winchester muzzle velocity and the actual muzzle velocity from your particular gun is likely to be even larger that those velocity prediction difference. So none of those predicted velocity differences are of any practical significance. When I run the ±3 inch MPBR calculator for those three drag functions for the Winchester round, I get 277 yards, 277 yards, and 276 yards for G1, G7, and G5 trajectories, respectively. Again, you'll get more error from shot-to-shot variation, and possibly much more from your particular rifle not achieving the same MV as the velocity test barrel did.

If you want more precision, and want to take the time to fuss with it:

Use both G1 and GL for a round nose bullet and figure real trajectory will be about half way between their results.

Use G7 if the bullets are secant ogive boattail bullets, such as VLD's and many of Hornady's current offerings.

Use both G5 and G7 trajectories for tangent ogive boattail bullets and pick results about half way between.

Use G6 for tangent ogive flat base bullets.

Use G8 for secant ogive flat base bullets.
 

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Discussion Starter #6
Nick,

Thank you for the extended information. I believe that the numbers dropped by the calculator work fine as general reference. I have perceived differences when comparing winchester powerpoints, core lokts and ballistic silvertips at the range, not just the drop but differences in groups at distances over 200 meters (220 yards), achieving tighter groups with the ballistic silvertip, followed by the core lokts and then by the power points. I also perceived that the ballistic silvertips maintained speed in a better way than the other two. However, I got these results from firing a few rounds, and I only made the experiment twice with two different rifles chambered for the same caliber.
 

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As you know, MPBR is determined by the height a bullet passes over the target, I usually sight in my big game rifles for a 4" (8" total target height), with most of my rifles that have similar trajectories, this works out to be 3" high @ 100yrds.
My varmint rifles are sighted to only rise 2" above the target, so it depends on the usage.
A lot of people like to sight in 2" high @ 100yrds for big game rifles, but the drop is significant at 400yrds with this type of sighting in and will cause misses for most beyond 400yrds.
I sight in my DG rifles to be point of aim at 50yrds for the most part, but my 375 Weatherby is sighted with the same 3" high @ 100yrds as my big game rifles, MPBR for that is a tad over 300yrds with a 270gr Woodleigh PP.
Point Blank is a free ballistics program, it works very well for working out MPBR and other ballistic notations.

Cheers.
:D
 

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In my experience the written tables are only a starting guide, normally if I have taken a scope off or something else that causes me to re-zero the gun I buy a box of those sporting clays targets and take them to the range setting them up in 50 yard increments out to whatever distance is appropriate for the caliber. Here in the west where shooting ranges have berms set up out to 500-600 yards this is an easy task.
There's a rabbit clay that's 6" in diameter I use for big game guns, center hold on the 100yard clay with a hit at 12oclock is a good start.
A 270 will probably require about a 300yard zero, 6.5 or 7mm magnums will be about 350yards assuming your using bullets with very good ballistic coefficients in mid-range weights.
With your 270 sighted in correctly you should be able to hit the 6" clay target using a center hold out to approximately 340yards, that's a guess.
Kb

Those little mini-clays are great for sighting in 17hmr, regular clays work well for 22 centerfires.

And yes this is a departure from my otherwise scientific approach to shooting but sometimes the redneck way is actually better.
 

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I am trying to figure out how to calculate the MPBR for popular calibers such as the .270 win (130 grains), .243 win (100 grains), .308 win (150 grains) and 30/06 (150 grains), for common factory loads, using the information given in standard ballistic charts. I am thinking about a small deer as a target (i.e. 15 inches from back to brisket). Thus, I think that the bullet shouldn’t rise more than 3 inches before starting to drop.
A 3" height of trajectory severely limits the useful range of these powerful rifles. Assuming pointed hunting bullets, they all have a good ballistic coefficient from ~0.3 to ~0.4 and muzzle velocities from 2800 to 3000 ft/s. For 0.35 and 2900 ft/s, you get a trajectory like this,
4"
100 200 300 400
3.35 3.27 -2.94 -16.6 Zero 265 yards

5"
100 200 300 400
4 4.6 -0.8 -13.8 Zero 290 yards

6"
100 200 300 400
4.6 5.8 0.8 -11.5 Zero 310 yards

7"
100 200 300 400
5.2 7 2.7 -9 Zero 330 yards

8"
100 200 300 400
5.7 8 4.1 -7.2 Zero 345 yards

If you zero for the longest likely range up to 345 yards and hold at the 6 o'clock position on the vital zone, you will get a clean kill without having to worry about hold over. Note that the trajectory is steeper beyond the second zero, so keep your game before that second zero and avoid estimating range/holdover for longer ranges by zeroing farther out. I've seen boxes labelled only to 200 yards. If you are guarding an open space with those calibres you can do a lot better from rest. Shoot some targets at the longer ranges. With a good rifle and ammunition one can have great confidence of proper placement. I was recently at our range with an 8mm Mauser and easily struck a deer-vital-sized gong at 200m standing with no difficulty at all. From rest I could easily reach 350 yards. I'm a shaky old guy well past my prime... :(

At long hunting ranges, accuracy, rather than height of trajectory should be your guide. If you can regularly place bullets into the vital zone, the height of trajectory doesn't matter if the bullet works and has enough energy. All of those rounds will reliably kill deer to 350 yards (243 would be marginal) and a bit further in some cases.
 

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Leupold has a LR Duplex reticle available in many of their scopes, combined with a good rangefinder solves most of the issues of the past with mpbr's.

Here's a VX-2 also have them in VX-1 and VX-3. Sight it in at 200yards and with most rifles the dots below correspond with 300and 400.

Amazon.com : Leupold 110801 VX-2 Rifle Scope : Sports & Outdoors
 

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Being in the Army from 1964-1966, unless you were a sniper, you used Kentucky windage, and calculated distance in you head, with good results. The same thing applied to hunting in Kentucky while with the 101st Airborne Division. Today, I do use a scope, Nikon Pro-Staff 3-9-40, which I love. I grew up with guns and hunting. I fired my first 22 when I was 5 years old and from then on it just got better. Nikon has a calculator which works great. I experimented and it does a good job. Living in Florida there is not much open range for hunting. You are lucky to get past 50 yards if that. I zero my Marlin 30-30 at a hundred yards and shoot 3 1/2" targets at a 100 yards. My results have always been within 1" grouping or less. However, that is with loading my own ammo. Factory ammo is another story-accuracy is no nearly as good. Still, with all the modern shooting equipment, breathing and trigger pull, I feel is still the most important. I enjoyed doing shooting competition while I was in the Army. The eye ball and judging the target distance is still a key factor. Calculators are handy but shooting without aids makes you a better shooter. Back in my younger days my brother and I use to shoot cotton tail rabbits on the run. Took lost of practice of course, but we only got better.

Dave
 

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Do y'all account for group size in these MPBR calculations? Seems to me that for example, if a gun shoots 4" groups at 350 yrds, and all the shots need to stay within an 8" diameter circle, then I should calculate the drop based on the center of the group. Which would be 2" +/- the center of the target in order to keep all shots within an 8" target with a 4" rifle at that distance.

If I did the calculation based on 4" +/- at the same distance, then added the group size, the actual impact area would be 12" in diameter as opposed to 8".

The kids kept me up half the night, maybe I'm missing something here while this first cup of coffee kicks in :D.
 

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Do y'all account for group size in these MPBR calculations? Seems to me that for example, if a gun shoots 4" groups at 350 yrds, and all the shots need to stay within an 8" diameter circle, then I should calculate the drop based on the center of the group. Which would be 2" +/- the center of the target in order to keep all shots within an 8" target with a 4" rifle at that distance.

If I did the calculation based on 4" +/- at the same distance, then added the group size, the actual impact area would be 12" in diameter as opposed to 8".

The kids kept me up half the night, maybe I'm missing something here while this first cup of coffee kicks in :D.
If you want to analyze the entire equation you would have to also factor in the what group size the shooters actually capable of shooting under field conditions.
My antelope hunting rifle is a 700 Remington in 7-08, it does double duty as a backup rifle for highpower silhouette, it wears a 6x18 Leupold with a dot and target knobs. Off a bench with no wind it is no problem to hit standard size clay targets at 200m,300m, 385m and 500m once zeroed.
Having said that I don't carry around a concrete bench to shoot off hunting, the wind always blows, more often than not the time frame to get a shot off is little more than a few seconds and laser range finders seem to pick the most inopportune times to not give a reading. Still you get lucky occasionally and it all comes together, I've killed a few pronghorns in the high 300's and low 400's, only lost 2 that were wounded which is not bad considering I've hunted them every year since 1977.
 
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