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Importance of T.O.F.???

 
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  #1  
Old 02-15-2011, 12:40 PM
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Importance of T.O.F.???

I'm trying to figure out why T.O.F. is not talked about more in comparison to B.C. and Velocity. Those 2 are the main ingredients in T.O.F. so why not cut to the chase and just give us that on a box of shells instead of advertising the B.C. and Velocity? Maybe I'm not getting the big picture but it seems to me that the single most important factor affecting long range performance is T.O.F.??? When comparing loaded ammunition it would make more sense if the manufacture's would the T.O.F. and Energy at X yards vs. B.C. and Velocity. They are all important but if you had to pick one factor wouldn't it be T.O.F.? See what happens when I have to much time on my hands!!!
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Old 02-15-2011, 03:08 PM
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Re: Importance of T.O.F.???

Shortpants,

TOF essentially is BC, it just hasn't been converted into a useful form yet. BC is simply TOF over a given distance, referenced against a standard that that particular table is based on and given an arbitrary and dimensionless number, usually "one". Knowing TOF over a given distance is useful for some calculations, and essential to some others (such as Coriolis effect). However, BC allows a great deal more flexibility in what sort of calculations can be derived.

You're just rockin' the boat here, aren't ya?!
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Lapua USA
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Old 02-15-2011, 04:33 PM
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Re: Importance of T.O.F.???

It just seems like it would simplify things a little to look at T.O.F. first as a way to compare if bullet X is better than bullet Y as far as long range ballistics is concerned.

For example,

Bullet X has a lower B.C. but higher Velocity than bullet Y causing bullet X to have a shorter T.O.F. than bullet Y.

Most people would make the argument that bullet Y will not drift as much as bullet X without looking at T.O.F. but that might not be the case. The bullet that stays in the air longer will be affected more by enviornmental parameters.

The way I understand how most people use a calculator is to get the actual velocity using a chrono and measure the enviornmental parameters and then plug in the info into a calculator and tweek it till find your true B.C. Only then can you rely on the drop and drift to be close (of coarse you have to go out and test the data). It seems to me if you could plug in your Velocity from your chrono and could some how enter your T.O.F. to lets just say 100 yards into the calculator it would be a more accurate way to calculate long range ballistics and cut out the tweeking part that seems to be a guessing strategy.

To make all that more simple let me just ask; if there was a way to measure T.O.F. and input it into your calculator do you think it would be a more simple system than the system described above?

I'm just thinking outloud again so if I'm not making any sense here just tell me to shut up. I'm still pretty new to long range ballistics and calculators so I'm just trying to learn from you smart fellers!
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Old 02-15-2011, 04:52 PM
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Re: Importance of T.O.F.???

Well, you're sorta backing into it here. TOF is the first step in determining BC, but you can also do it with two velocities at different distances as well. You have to remember, velocity IS TOF over a measured distance, and nothing more. What we're measuring here is drag deceleration, or how much velocity the bullet in question is shedding over a given distance. If you use the tables themselves (and you can find the Ingall's tables--roughly equivalent to the G1 drag model--in Hatcher's Notebook) you'll see there's both a time and space function. He also explains in detail how the calculations are done, and you can do your own. It's not difficult, just a bit tedious. Personally, I think everyone should at least give it a try, so they have some idea of what's involved rather than just punching numbers into a computer. Sort of like learning to do math WITHOUT a calculator, before you start using one for all your math problems. It just gives you a clearer understanding of what you're looking at, rather than what may seem like a bunch of random numbers.

I think part of the problem that we're dancing around here is the fact that TOF would be drastically different, depending on what part of the bullet's flight you measured it over, how far it was measured, etc. . Drag deceleration and velocity loss is anything but constant. It changes substantially, with the greatest percentages of loss occurring at the highest velocities, and becoming much less as the bullet slows. Remember, atmospheric resistance is roughly proportional to the square of the velocity; halve the velocity and you've reduced the resistance by a factor of four. Double the velocity, and you roughly quadruple the resistance. Using BC, and an appropriate drag model accounts for this, and will give more accurate calculations at all distances of the bullet in question's flight.

Whew! That was a windy one!
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  #5  
Old 02-15-2011, 06:08 PM
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Re: Importance of T.O.F.???

Short answer is that its not more simple because ToF will be different for every rifle, even if they use the exact same ammo, becuase the muzzle velocities will be different.

Additionally, changing the status quo with large corporate ammo manufacturers? - youd have more success punching a hole in a brick wall with your head...
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Old 02-15-2011, 07:47 PM
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Re: Importance of T.O.F.???

I think you're seeing it backwards. You can't predict TOF without BC, so why not just use BC?
And then there is the matter Kevin mentioned that TOF itself, is not a direct indicator of BC. If I shot a high BC slower, it's TOF would be higher from distance X to Y. So even if there were a 'standard' velocity and X&Y points on the box, if I'm launching them at another velocity(not standard), then I'm stuck interpolating, guessing, adjusting and testing as much as we must with BC!
I can't think of a real gain there..

There is another factor that would pull any nobel prize off from under your notion; TLAG
A ballistic system can have seperate attributes of drift-vs-drop for near wind -vs- far wind.
I think it could actually lead to two BCs assigned in the future(atleast for me).
Wind drift is tied to velocity loss RATE(this is not TOF). Low BC bullets launched at very high velocities(low TOF) loose velocity at a higher rate than high BC bullets launched at low velocities(hi TOF). Given this, near wind pushes the largest velocity drop rate(esp. w/lower BC bullet) to cause a greater angular error down range, than it would for the lower velocity loss rate bullet.
Most(not all) ballistic programs assume wind entry applies to the full bullet flight, but it's really the first couple hundred yards of wind that dominates results. It's the first couple hundred yards that a bullet's velocity loss rate is highest.

Anyway, it's fun to think about something that is new and different here
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Old 02-15-2011, 08:46 PM
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Re: Importance of T.O.F.???

Quote:
Originally Posted by shortpants View Post
The bullet that stays in the air longer will be affected more by enviornmental parameters.
The problem is the above assumption is incorrect. A high BC bullet starting slower will drift in the wind less than a low BC bullet if their time of flight is identical.

Think of the phrase "affected by environmental parameters" you used above. The best measure of that is how much velocity is lost on the way to the target, not the average velocity to the target. In the case above, both bullets average the same velocity to the target. The low BC bullet starts faster, ends slower which means it lost more velocity along the way. This means it was more "affected by the environment" than the high BC bullet. If the air slowed the bullet down more, it also pushed it sideways farther.

So as you can see, as far as wind drift is concerned, BC is a much more important value than TOF for any given distance. For drop, yes, TOF is what matters. But that's easy.
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