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Flatness of trajectory

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  #1  
Unread 06-25-2004, 01:10 PM
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Flatness of trajectory

Flatness of trajectory is usually measured in terms of absolute bullet drop. However, there are instances where one bullet may experience less bullet drop at a give distance, except a different bullet may actually have more Danger Space at that distance. This is often the case where one bullet has a higher muzzle velocity except loses its velocity very quickly, whereas another bullet has a slower muzzle velcoity except retains its velocity better.

In the case of shooting at long range targets of unpsecified distances, which is more important, less absolute bullet drop or more Danger Space?
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  #2  
Unread 06-25-2004, 05:12 PM
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Re: Flatness of trajectory

Whoa!! and your title is newbie_71??

We don't generally talk about "Danger Space" here so some folks are probably not familiar with the term. Perhaps a short explanation would be in order, care to give one. (It'd help some. Thanks)


Less absolute bullet drop equates to more danger space. I believe where you're headed is "should I pick a lighter and possibly lower BC bullet for my shooting and reap the short range less drop danger space increase/benefit OR go for a heavier, high BC bullet and suffer with a rainbow trajectory and lesser danger space". If I were to be shooting at unknown and/or accurately determined ranges I'd probably opt for the faster bullet and increased danger space but this limits/decreases the longer range energy/speed. Once I take on the method of knowing the range accurately I can choose the bullet with the colorful trajectory and reap those benefits.

Hope this helps some.

[ 06-25-2004: Message edited by: Dave King ]

[ 06-26-2004: Message edited by: Dave King ]
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  #3  
Unread 06-25-2004, 08:24 PM
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Re: Flatness of trajectory

What about in a situation like this? For example, a .223 Remington - 52 grain Sierra BTHP MatchKing launched at 3,240 feet per second experiences 123 inches of absolute bullet drop at 600 yards. A .308 Winchester - 175 grain Sierra BTHP MatchKing launched at 2,580 feet per second experiences 127.6 inches of absolute bullet drop at the same distance. This would generally lead people to define the first cartridge as the "flatter shooting" of the two at the specified distance.

However, if the shooter attempts to estimate the distance and makes an estimate of 590 yards, he would shoot 3.9 inches low with the .223 Remington and 2.8 inches low with the .308 Winchester if he was able to zero each in at 590 yards.

This is, of course, neglecting to factor in that he must make adjustments in increments of what his scope allows. Let's assume he makes 1/8 MOA adjustments and was originally zeroed for 200 yards. With the .223 Remington, he would make 65 clicks and still hit .1 inches high at 590 yards. With the .308 Winchester, he would make 67 clicks and hit .2 inches low at 590 yards. The interval-induced errors of.1 and .2 inches actually fall on the side of the.223 Remington in this case since the .223 Reminton is hitting slightly high, the .308 Winchester is hitting slighlty low, and the target is farther away than was estimated (It could have every bit as easily fallen on the side of the .308 Winchester, except that is an entirely different matter that merely muddies up the issue). However, since the target was actually farther away by 10 yards, the .223 Remington will strike 3.8 inches low and the .308 Winchester will strike 3 inches low. If it wasn't for the "issue muddying" errors induced by the limit of 1/8 MOA adjustments on the scope, the result would have been 3.9 inches low for the .223 Remington and 2.8 inches low for the .308 Winchester.

This results in a situation where the bullet with the least amount of flight time, and corresponding bullet drop, actually allows the shooter less tolerance for error in approximating the distance to the target. However, in terms of the number of clicks on the scope the .223 Remington only requires 65 clicks and the .308 Winchester requires 67 clicks.

There is yet the issue that I counted a MOA adjustment on the scope as making an adjustment of 1.047+ inches, as opposed to 1 inch. I'm not sure if this is correct. Also, I assumed standard atmospheric conditions and strict adherance to a specific Drag Curve (probably the wrong one actually) with a static Ballistic Coefficient. Still, the point is that the bullet with the least amount of bullet drop and typically greater MPBR is not neccisarily the one with the biggest Danger Space at longer range as a result of the fact that the parabolic trajectory of a bullet is not a pure parabolla, except a changing one and some change differently than others.

In Summary, what do you feel is more significant, absolute bullet drop, number of clicks on the scope, or increased Danger Space?
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  #4  
Unread 06-25-2004, 09:48 PM
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Re: Flatness of trajectory

To me i would chose the 308. To me i see the 308 shooting flatter. I say this because the 175 is going (in this example) 600fps slower than the 223 and arriving at the same point a couple of inches lower. Not to mention the B.C. of the 175 is considerably higher than the 52 grain and the 175 will have a better wind bucking ability which the wind will be more of a factor for anyone versus the range(If one practices and not throws hail mary's).The 175 will also retain more energy.

Maybe i am thinking wrong or don't understand the question?

[ 06-25-2004: Message edited by: Matt27 ]
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  #5  
Unread 06-25-2004, 10:27 PM
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Re: Flatness of trajectory

Newbie
Sounds like you've already done lots of homework on this one but here is my opinion anyway.
Don't get too hung up on the difference between calibres and BC's and their trajectory relationship to your scope's elevation adjustments . Very few people are good enough field shots to hold within 1/4 MOA let alone 1/8 . Your ability will be the governing factor .
Secondly on velocity vs BC . Generally a bullet with the shortest time of flight would be best in still conditions at shorter yardages and particularly where a rangefinder isn't available . However as you have discovered inevitably you will reach a range where the high BC projectile's velocity exceeds that of the low BC pill . From that point on its all in favour of the high BC . What range the crossover occurs at obviously depends on velocity and BC differentials of the 2 projectiles . In the case of .223 vs .308 the velocity differential is not huge so the crossover occurs much closer in than would be the case with .220 Swift vs .308 .
In order to make the correct decision you need to decide what range you will be doing most of your shooting at and also whether wind is a factor . It's much harder to measure and deal with than straight bullet drop .
If you want the best of both worlds choose a cartridge that can fire a high BC (.500 plus) projectile at 3300 FPS or better .
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  #6  
Unread 06-26-2004, 06:03 AM
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Re: Flatness of trajectory

Newbie

Good topic... I like it but it's difficult to make a one situation fit's all decision.

Here's a chart of the data for the two examples you provided (STP and initial BC is correct for muzzle speed 223=.225 and 308=.496).



What I gleaned from this chart is that the break even point for comparing these two rounds is 630 yards. Beyond 630 yards the 308 and the 175 clearly have the advantage in trajectory (no consideration of energy).

I you inital post I thought you were talking about the same rifle/cartridge and different bullets. Seems you were talking different rifles and cartridges.

I personally consider 500 yards as the general break point for bullet/cartridge selection. Inside 500 yards a light fast bullet (lower BC) probably has a slower heavier bullet (higher BC). That being said, my danger space consideration for shots inside 500 yards would go to the light fast types, beyond 500 and I'll pick the slower heavy (high BC) type.

Of course Aussie is correct in that one must consider the heavy fast launcher like the big magnums, these are the favored better choice but the down side is they eat barrels and are a little more user unfriendly.

For your stated scenario, I'd pick the 308.

Once again, good topic. There are other things we can consider, target area (vertical size and depth), critters are three (3) dimensional and not like the two (2) dimensional practice version called paper or steel.
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  #7  
Unread 06-26-2004, 08:04 AM
GEG GEG is offline
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Re: Flatness of trajectory

I think I figured out what "Danger Space"
is by reading the post but can someone give me a for sure definition? Thanks GEG
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