Flat Trajectory Benefit


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eric.cartman
February 11, 2008, 04:42 PM
Correct me if I'm wrong...
Does a flat trajectory make it easier to adjust the scope for a different distance? Say I have a scope set to 100 yards, then I want to hit something at 200. Is it more accurate / reliable / easy to set it when I use a round with flatter trajectory?

Also, is .308 Win considered a flat trajectory round?
If not, what sniper round is?

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waterhouse
February 11, 2008, 04:56 PM
If you have to adjust the scope I don't know if it makes it "easier" . . . turning the elevation knob doesn't take much effort, and turning it a few extra clicks doesn't take much more effort.

No matter what you use, you'll need to know its drop at different distances.

What a flat trajectory does make easier, IMO, is an increased MBPR, which means you won't need to adjust the scope at all until some further distance.

rcmodel
February 11, 2008, 05:17 PM
+1

With a flat shooting rifle you can just zero it at 200 - 250 yards and not have to change the scope at all. The bullet path will be very near the scopes zero from the muzzle out to 300 or more.

For a 22-250 for instance, you could zero 1 3/4" high at 100 yards, and the bullet would hit POA at 250 yards, and still be only 3" low at 300 yards.

Zeroing a flat shooting rifle at 100 yards and then fiddling with the scope for longer range is a waste of time, and the rifles full potential.

http://i81.photobucket.com/albums/j219/rcmodel/KTOG/1224.gif
rcmodel

Black Jaque Janaviac
February 11, 2008, 06:00 PM
Yes flatter trajectory means easier scope adjustments.

A flat trajectory means a longer point blank range. For example if you want to hit a deer at 300 yards with a .30-30 you'll have to make some sight adjustments and/or "hold high". With a .308 win you would not need to make any adjustments. That's because the .30-30 has a point blank range of 200 yards and the .308 has a point blank range of 300 yards (roughly speaking).

Beyond point blank range the flatter trajectory still has a great advantage. At say 500 yards the .30-30 and the .308 can still make effective hits on targets. However, the .30-30 bullet (which can be less aerodynamic) is dropping faster at 500 yards than the .308. That means that between 500 and 525 yards the .30-30 may drop 8 inches, whereas the .308 might only drop 3 inches. If you know your target is exactly 500 yards away this may not have much affect. So if your distance estimation is +- 25 yards this makes the difference between a clean kill and a miss, or worse a crippler. So can you tell the difference between a 500 yard shot and a 525 yard shot? Because if you can't, depending on your firearm there may be a big difference in point of impact.

Also, flatter trajectory rounds often have better wind-drift ballistics. So if there is a 10 mph side wind the flatter trajectory bullet will often drift less. This is a loose correlation so you really need to check wind drift tables to verify this.

Zak Smith
February 11, 2008, 06:10 PM
BJJ's analysis is spot on. I'll just add some other points:

Most regular full power rifle cartridges like .308, 30-06, 270, etc, have a point-blank range of 250-300 yards if you can accept a +/- 3" deviation from the point of aim. Marginal increases in PBR due to increased cartridge power/velocity incur vastly increased costs in recoil, ammunition cost, and barrel life.

Once you get past this PBR range, you have to dial, and the drop rate BJJ alludes to is a factor, however, even with a 308 which has 47% more drop per yard than 7 Rem Mag at 700 yards, most long-range misses are due to windage error. And BC is the dominant factor in reducing wind drift.

-z

W.E.G.
February 11, 2008, 07:53 PM
http://en.wikipedia.org/wiki/Point-blank_range

I want to reformat my brain so I can use the extra space for just for pleasure.

Wikipedia knows everything I need to know about "stuff."

UnTainted
February 11, 2008, 09:30 PM
the bullets fall at the same speed down, it's their velocity that gets them to farther ranges faster that makes them seem like they drop less than calibers that drop more.

Thus, fast bullets (that carry their speed too) will have the longer "point blank" range.

faster to target means less time for wind to have an affect as well (and larger caliber, say a .30 cal will have more surface area on the side for wind to exert energy than a smaller cal like a 243 or 270.

If you want a really flat shooting caliber, a friend of mine likes the 270WSM for elk, and has taken to 475 yards with it off a horses back (yes, that's bad for the horse, he knew it).

think about how sweet the 270WSM would be in an ar-10 conversion with a 26" barrel!!! Oh man...

Zak Smith
February 11, 2008, 09:34 PM
faster to target means less time for wind to have an affect as well
This is not true, strictly speaking.

For example:


_Bullet_ _BC_ _MV_ 0 200 400 600 800 1000 | YARDS
300/155LAP 0.508 3300 > 0.00 0.19 0.41 0.66 0.95 1.28 | time (sec)
0.00 2.01 8.48 20.31 38.58 64.70 | wind (inches)
300/210VLD 0.640 2900 > 0.00 0.22 0.46 0.73 1.03 1.36 | time (sec)
0.00 1.88 7.88 18.67 35.03 57.93 | wind (inches)


or


_Bullet_ _BC_ _MV_ 0 200 400 600 800 1000 | YARDS
243 70NBT 0.310 3300 > 0.00 0.20 0.45 0.76 1.16 1.66 | time (sec)
0.00 3.40 15.06 37.93 76.13 132.59 | wind (inches)
308/175SMK 0.51* 2600 > 0.00 0.25 0.53 0.86 1.25 1.70 | time (sec)
0.00 2.87 12.28 29.72 57.10 96.01 | wind (inches)

Black Jaque Janaviac
February 13, 2008, 06:09 PM
Quote:
faster to target means less time for wind to have an affect as well

This is not true, strictly speaking.

Which is why I said the correlation between trajectory and wind drift is loose. Also smaller caliber bullets aren't necessarily the better choice for wind drift.

The vertical trajectory is fairly uniform because the acceleration due to gravity is constant no matter how heavy the bullet is. However the force that a cross wind applies on a bullet doesn't increase as bullet weight increases. So the heavier bullet has more inertia to resist the cross wind.

ArmedBear
February 13, 2008, 06:17 PM
Shoot a jackrabbit at a good distance with a black powder .45-70 and the benefit of a flat trajectory will become clear.

Zak Smith
February 13, 2008, 07:14 PM
However the force that a cross wind applies on a bullet doesn't increase as bullet weight increases. So the heavier bullet has more inertia to resist the cross wind.
This is already rolled into the BC.

UnTainted
February 13, 2008, 07:24 PM
faster to target means less time for wind to have an affect as well
This is not true, strictly speaking.


Sure, between different bullets and weights yes, but between the same bullet with same BC, it's a true statement. Thus, my statement wouldn't be true under your conditions of different bullets, and would be under my condition of only changing the variable of speed.

To both our scenarios and statements, the Barnes MRX bullet should excel in long range shooting, especially with a flat-shooting caliber

Zak Smith
February 13, 2008, 07:28 PM
If we're talking about choosing cartridges for LR shooting, it seems natural that statements would be taken in a broad context; not a very narrow context which was not made explicit. I think everyone knows that if you nudge a load a little faster it'll have less wind drift.

-z

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