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280 rem trajectory doesnt seem right

 
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  #1  
Old 10-29-2012, 11:47 PM
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280 rem trajectory doesnt seem right

hey guys new to forum and long range shooting....i have a semicustom 280 rem shooting 1/2 groups at 200yds with 168 gr berger at around 2800fps..... havent found zero yet but im 3" high at 100 and 4" high at 200...this doesnt seem right??? seems like i should start dropping by 200yds?? Could scope be mounted off plane?? or does the trajectory sound right? ...have somewhat the same issue with a 257 wby same exact scope/base/ring set up....leupold vxlll 4.5-14x50/one piece std base/30mm rings
thanks
both rem 700 actions
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  #2  
Old 10-30-2012, 08:37 AM
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Re: 280 rem trajectory doesnt seem right

Nothing strange about that.

You're 3 MOA high at 100, and only 2 MOA high at 200. The bullet is dropping, it just happens to still be above the aim point.

when you zero for long range, say 600 yards, you could be 12" high at 100 yards, and 22" high at 200 (for example) because the bullet will climb for about 300 yards before beginning to drop down to the zero at 600.

Come down 3 MOA to zero at 100 and you'll be about 2" low at 200.

-Bryan
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And: Accuracy and Precision for Long Range Shooting

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  #3  
Old 10-30-2012, 09:09 AM
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Re: 280 rem trajectory doesnt seem right

Agree with Bryan... but I'll add this...

I've seen "weird" 100 versus 200 yard zeros more with light weight, sporter barrels than with heavy barrels.

There are dozens of explanations as to why this happens, so brace yourself.

In my opinion, it has to do with the whipping direction of the barrel when the bullet is released from the muzzle.

Check these animations from varmint al... Barrel Harmonics Mode Shape Movies

So... the position of the muzzle at bullet release has a direct effect on where the bullet crosses the line of sight. Your scope of course looks "dead straight" at the target. Your bullet, however, must rise to cross the line of sight (since the barrel is below the scope), then begin its fall toward the zero point of the scope.

If the bullet crosses the line of sight closer to the 100 yard point, it may still be rising at the 100 yard point. The bullet is likely continuing to rise, even past the 100 yard point, then it will begin to fall... and by the 200 yard point, it's higher than you'd think it would be.

Check your 150 yard zero... we've seen seasoned long range shooters at our rifle matches who can ring the plate at 800... 900... and 1000 yards darned near every time.... but a playing card at 165 yard causes them all sorts of grief. Most folks never plot their 165 yard zero, so they really are often surprised to find out just where it really is (ballistics drop charts don't generally agree with reality in this range)...

If you zero your rifle for a 200 yard zero (drop the scope elevation 8 clicks)... that would put your 100 yard point of impact only an inch above the crosshairs, and you'd have a "point blank range" of 275 yards, perhaps a little more. Meaning just hold right on and shoot, all the way to the extent of your point blank range.

In short, it doesn't seem that your rifle is doing anything that much out of the ordinary. I've seen far more exaggerated examples of what you're describing--which is why I offered my explanation/theory as to what's causing it.

Dan
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  #4  
Old 10-30-2012, 12:05 PM
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Re: 280 rem trajectory doesnt seem right

hey thanks guys...makes me feel better
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  #5  
Old 10-30-2012, 01:05 PM
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Join Date: Oct 2012
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Re: 280 rem trajectory doesnt seem right

one more question...when i plug in my #'s to the ballistics calculator if im 3" high at 100 yds it says i should be under 3 at 200yds...according to it ,to have my trajectory
(3 at 100/ 4 at 200) id have to be shooting 4700fps( im new but i know thats wrong)....am i reading the trajectory wrong? sorry guys like i said im new...what exactly does drop on ballistics charts represent? is it the drop from point of aim or point of barrel plane?
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  #6  
Old 10-30-2012, 01:40 PM
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Re: 280 rem trajectory doesnt seem right

The drop chart cannot anticipate the point at which your bullet crosses the line of sight, therefore it doesn't know with certainty whether the bullet is still rising at 100 yards or whether it has begun its descent.

The chart assumes that the bullet has begun its descent by the 100 yard point, falling back through the line of sight at or very near 100 yards (after first rising thru the line of sight sometime around 40 to 60 yards or so).

This is why you have to "true" your chart. You'll likely not find a perfect program that gives you accurate drops for all ranges...

What you can do is set your zero for 200 yards, by which time the bullet is definitely falling, and plot your drops from there on out. Then make some notes on the data card indicating your 100 yard to 175 yard "hold under"...

Dan
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  #7  
Old 10-30-2012, 02:54 PM
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Re: 280 rem trajectory doesnt seem right

Quote:
Originally Posted by green 788 View Post
The drop chart cannot anticipate the point at which your bullet crosses the line of sight, therefore it doesn't know with certainty whether the bullet is still rising at 100 yards or whether it has begun its descent.
If you output your chart in small enough range increments, you can tell if it's rising or falling at the 100 yard zero. Consider the output below in 10 yard increments, you can see that the trajectory rises slightly above the line of sight before 100 yards, then falls down to the zero point at 100 yards, and continues to fall beyond that. With a faster MV, and a higher sight height, the bullet could very well still be rising at 100 yards, which the drop chart would show if the range increment is small enough.

Code:
      Range    Velocity    Energy     Trajectory         TOF          Drift
      (yards)     (fps)     (ft-lb)     (inches)         (sec)       (inches)
          0      2600        2326          -1.50         0.0000         0.00
         10      2581        2292          -1.11         0.0116        -0.01
         20      2561        2258          -0.76         0.0232        -0.03
         30      2542        2224          -0.47         0.0350        -0.07
         40      2523        2190          -0.24         0.0469        -0.12
         50      2504        2157          -0.06         0.0588        -0.20
         60      2485        2124           0.07         0.0708        -0.28
         70      2466        2092           0.14         0.0829        -0.38
         80      2447        2060           0.15         0.0951        -0.50
         90      2428        2029           0.10         0.1075        -0.64
        100      2409        1998          -0.00         0.1199        -0.79
        110      2391        1967          -0.16         0.1324        -0.96
        120      2372        1937          -0.39         0.1450        -1.15
        130      2354        1907          -0.68         0.1576        -1.35
        140      2335        1877          -1.03         0.1704        -1.57
        150      2317        1848          -1.44         0.1833        -1.81
        160      2299        1819          -1.92         0.1963        -2.07
        170      2281        1790          -2.46         0.2094        -2.35
        180      2263        1762          -3.07         0.2226        -2.64
        190      2245        1734          -3.75         0.2360        -2.95
        200      2227        1706          -4.50         0.2494        -3.29
        210      2209        1679          -5.32         0.2629        -3.64
        220      2191        1652          -6.21         0.2765        -4.00
        230      2174        1626          -7.17         0.2903        -4.39
        240      2156        1600          -8.20         0.3041        -4.80
        250      2139        1574          -9.31         0.3181        -5.23
        260      2121        1548         -10.50         0.3322        -5.68
        270      2104        1523         -11.76         0.3464        -6.15
        280      2087        1498         -13.10         0.3607        -6.64
        290      2069        1474         -14.52         0.3751        -7.15
        300      2052        1450         -16.03         0.3897        -7.68
        310      2035        1426         -17.61         0.4044        -8.23
        320      2018        1402         -19.28         0.4192        -8.81
        330      2002        1379         -21.03         0.4341        -9.41
        340      1985        1356         -22.87         0.4491       -10.02
        350      1968        1333         -24.80         0.4643       -10.67
        360      1951        1311         -26.82         0.4796       -11.33
        370      1935        1288         -28.93         0.4951       -12.02
        380      1918        1266         -31.14         0.5106       -12.73
        390      1902        1245         -33.43         0.5263       -13.46
        400      1885        1223         -35.83         0.5422       -14.22
        410      1869        1202         -38.32         0.5582       -15.00
        420      1853        1182         -40.91         0.5743       -15.81
        430      1837        1161         -43.60         0.5905       -16.64
        440      1821        1141         -46.39         0.6070       -17.50
        450      1805        1121         -49.29         0.6235       -18.38
        460      1789        1101         -52.30         0.6402       -19.29
        470      1773        1082         -55.41         0.6570       -20.22
        480      1757        1062         -58.64         0.6740       -21.18
        490      1741        1043         -61.98         0.6912       -22.17
        500      1725        1025         -65.43         0.7085       -23.19

Quote:
The chart assumes that the bullet has begun its descent by the 100 yard point, falling back through the line of sight at or very near 100 yards (after first rising thru the line of sight sometime around 40 to 60 yards or so).
The chart assumes no such thing. If you only look at the output in 100 yard increments, YOU can't tell if it's rising or falling, but the ballistics program that generated the chart *must* know the state of the bullet (rising or falling) on a continuous basis thruout the trajectory, even if it's just outputting every 100 yards.

Quote:
This is why you have to "true" your chart. You'll likely not find a perfect program that gives you accurate drops for all ranges...
The reason for ballistic program predictions not lining up with observed drop can almost always be attributed to inaccurate inputs. If you input accurate data into a good ballistics program, it will calculate an accurate trajectory at least over the supersonic range of the projectile. This has been documented many times. Admittedly it's difficult to get all the variables truly accurate, but if you do, the predictions are valid without correction.

Quote:
What you can do is set your zero for 200 yards, by which time the bullet is definitely falling, and plot your drops from there on out. Then make some notes on the data card indicating your 100 yard to 175 yard "hold under"...

Dan
You could do that. Typically I advise shorter range zeroes because it makes the zero less susceptible to conditions, wind, etc. If you want a long PBR for quick engagements, it makes sense to consider a longer range zero.

Dan,
I'm not attacking you or trying to be contrary for the fun of it. Just offering a new guy multiple perspectives to consider. No offense intended.

-Bryan
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And: Accuracy and Precision for Long Range Shooting

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