# Bullet flight path

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Whitetail Hunter, Oct 17, 2004.

1. ### Whitetail HunterWell-Known Member

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My local range only has targets out to 300 yards. I have a 100 yd zero and my come up for 300 is about 2.7 MOA. I asked to shoot on a farmers field to 500 yds. My come up and 400 is 6 MOA and 500 yds is 9.6 MOA. The bad part is I don't know my velocity. I am shooting 200 accubonds with 91 gr of H-1000. My book velocity should be close to 3000 fps. According to my actual values to the caculated I am more than a 1 MOA off at 500 yds. Is this typical?

2. ### Ray MeketaWell-Known Member

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Craig

When you say "calculated" I assume you mean one of the ballistic programs. The short answer is, yes, you could be that much off if you don't know the velocity. That's one of the critical numbers in your input data. Ballistic programs are not perfect. If you have actual come-ups you have to trust them and not some program numbers.

3. ### Whitetail HunterWell-Known Member

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cheechako,

I just didn't think that the ballistic programs would be that far off at 500 yds already I gues that my next shooting gadget should be a chronograph.

4. ### Whitetail HunterWell-Known Member

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The caculated velocity was taken from the Nosler manual

5. ### 700Well-Known Member

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Craig

I assumed the following for your situation.

Min. Possible Velocity : 2700 fps
Max. Possible Velocity : 3300 fps

Min. Possible G1 BC : 0.45
Max. Possible G1 BC : 0.6

Scope Height = 1.5 inches

Standard Athmospheric Conditions

Using some computer code I wrote over the weekend, and a method of least squares, I found that a G1 BC of 0.45 and an MV of 2970 fps suits your drop data quite well.

These values may not even be close to your true BC or Muzzle Velocity but they should produce a pretty decent drop chart from a ballistics program,which will match the data you gave us quite well.

Range Yrds,,Drop In,,Drop MOA
100,0,0
200,-2.70527,-1.29167
300,-10.6921,-3.40342
400,-25.3806,-6.05917
500,-48.6858,-9.29832

Using this
You will be on target at 100 yards.
You will be 0.8 MOA low at 300 yards.
You will be 0.059 MOA low at 400 yards.
You will be 0.3 MOA high at 500 yards.

Hope this helps

Regards

700

6. ### 700Well-Known Member

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Craig, Cheechako

It is well to remember that ballistics programs can only approximate a bullets flight path.

The G1 ballistic coefficient which most programs use was origionally developed for a particulat projectile. The G1 BC will work great if you you are shooting that particular projectile, but less well, the more different your projectile is from the origional intended projectile.

Rgds

700

7. ### Whitetail HunterWell-Known Member

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700,

thanks for the drop chart. My scope height is 1.8" how did you develop that caculation?

8. ### MysticplayerWell-Known Member

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Craig, your observations are indeed 'correct'. Programs make a lot of assumptions that unless adjusted for, will give erroneous results.

You have to adjust for humidity, temp, elevation, barometric pressure, true BC of bullet out of your rifle, true muzzle vel, accurate measured distance, etc.

If you ranged your distance with a laser rangefinder, your reading may be consistent but out. All rangefinders have a degree of error in their readings. So your 500yd reading, may actually be 485yds or something like that.

Your turrents may not be adjusting perfectly 1/4 MOA per click. If it were a bit off either way or changed slightly as you went up in rotations, you will get different results. As long as the results are consistent, the actual number really doesn't matter.

I use a Leica 800 to get my distances. Whether it is off or not, really doesn't matter. It is consistent. My drop table is based on one load, one scope and one rangefinder. Doesn't really matter if the true numbers are different from what I use.

I range a target, dial up, aim and shoot. A hit results. That is all I want from my gear.

Recent shooting with my 6.5-06 and 140gr SST highlights the problem with believing a program is absolute. With the adjustments I need and the muzzle vel of the bullets, the BC is seriously goofy as it comes from the program. The BC is high for sure, but over 0.8? Probably not.

However, the gear is consistent and repeatable which is what you need to have the confidence to shoot at LR.

Jerry

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You have to adjust for humidity, temp, elevation, barometric pressure

Jerry, how do you get a local barometric reading you can count on?

...especially when you are out west hunting?

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11. ### Whitetail HunterWell-Known Member

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Jerry,

My rangefinder is a Lecia 1200. My scope is a Nikon 6.5 to 20 with 1/8 Min clicks. i do see your point about using one rifle one load and one rangefinder to eliminate any errors. I know that my MOA adjustments aren't perfect because I am using a 6" bull for zero. I figure if I can hit that consistently and those ranges I am good to go. Leaving this week for a elk hunt in MT. After reading several posts and seeing some of the drops it feels like bullets are crawling along I don't plan on shooting past 400 but I thought it would be good to 500 just in case...

12. ### Jeff In TXWell-Known Member

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Len,

I use the Krestel 4000 weather/wind meter. When I get off of the plane at the airport, I check with local weather or airport weather on the net and I adjust my krestel to match the BP. I work from there. It's not a perfect match, but as close to it as I can get.

I also don't fuss much with humidity. It has a very limited effect on a bullet, maybe 0.5 MOA at 1000 yards

13. ### MysticplayerWell-Known Member

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Len, this should get you the ballpark. http://www.theweathernetwork.com/weather/cities/indexbc.htm

Just look up a city and it will show the barometric pressure usually from a local airport or environment station.

Not perfect but should be close enough for what we are doing.

Another option are the new generation GPS for mountaineering. They come with a climate mode which will measure pressures. How accurate? No clue. Comparing the two should get you in the right ballpark.

Craig, 200gr of really big bullet leaving at 3000fps is plenty big medicine for even the western kevlar skinned elk at ranges well beyond your comfort zone.

I would not hesitate to shoot one at up to 700 yds with my 6.5-06 and 140gr SST. On a broadside shot, I doubt I would find a bullet.

Your problem will be trying to hit the elk from field rests and naturally windy conditions. You bullet will certainly be lethal enough.

Nikon are very good mechanically but I would still do this torture test.

Go somewhere you can shoot rocks at ranges from 200 to 500yds. Just somewhere safe in the back 40. From the rests you plan on using, set up, range a rock about the size of the kill zone on your elk, dial up, shoot it. One shot one hit - yes or no. Reset scope to 100yd zero. Only take one shot per rock. No sighters at this range.

Let barrel cool, range another, dial up, etc. Keep repeating and you will quickly find how consistent you and your drop table are.

Now increase test by running the elevation knob through its entire range once or twice, then back to zero and dial up. Does it still hit where it is supposed to?

You will be amazed at the number of big dollar scopes that will fail this test. Their owner will claim that they need to dial past then back or only turn the knob slowly or only on Wednesdays after a full moon.

Hoogwash. I want my turrents to go to where I need right now. No mucking about and tweaking. In the field with your trophy deciding to leave the zip code, you need to know that I range, dial up, squeeze and start gutting.

Or else, get a whole bunch closer or get a better scope.

More practise. Stand up and move a round for a bit. Get back into field position, range another target, dial up, etc. Stand up, etc.

Keep repeating it until you gain the confidence to make that cold barrel shot hit. It is harder then it sounds. don't wait for calm days, in fact the worse the weather the better. You need to know what your load is likely to do in those Mountains.

Now increase the task. Go for a brisk walk or jog. Repeat the test and fire in under 10seconds. I think you see where this is going. Always start from your hunting zero on your turrent.

We all test our gear but do we ever test ourselves and that gear. I quickly found that scope eye relief was not right on one rifle, trigger weight not right on another, not field accurate enough for another.

All problems were eventually solved but they did not show up on the range. Test as you are going to hunt. That is the only way to know and for most of us, improve our confidence immensely.

My biggest problem now is finding them but that's another story...

Jerry

14. ### Whitetail HunterWell-Known Member

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Jerry,

thanks for your input and explanations. Thanks to all for your help. Sounds like practice, practice and practice which is fun for me.