Flatness of trajectory

[Newbie]

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?

 

[Dave King]

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 ]

 

[Newbie]

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?

 

[Matt27]

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 ]

 

[Aussie]

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 .

 

[Dave King]

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.

 

[GEG]

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

 

[Brown Dog]

Newbie,
Interesting thread! My head demonstrated rather low bandwidth reading all this -had to re-read everything a couple of times to get the issues straight in my head!

Range (mis)estimation would appear to be the root of all problems that could arise in your scenarios. Determining the opening range shouldn't be an issue if you have a laser; issues may arise if the target should move closer/further between obtaining the opening range and your 1st shot or between 1st and subsequent shots.

If range (mis)estimation –for whatever reason- is of concern to you, I think what you're after is the round that gives you the 'least plunging' trajectory at the ranges at which you are likely to shoot (ie what you're describing as the greatest 'danger space'.)


GEG,
I must say that I too was a little confused by the use of the term 'danger space' here.
It is a military term used in the context of machinegun or harassing sniper fire.
It's similar to the idea of 'beaten zone' but takes account of targets being vertical rather than horizontal; so (in very ballpark terms) with a centre hold on an avg 5.5ft man, the danger space for a 308 with sights set at 800yds would start if he was actually standing at 700-and-a-bit yds (ie the trajectory would start to clip the top of his head) and end if he were actually standing at 850-and-a-bit yds (ie it would clip his toes).
I think what's being referred to here is 'the ranges between which the trajectory will remain in the animal's vital area at a given sight setting' which is not the same as the military concept of 'danger space', but 'danger space' certainly sounds sexier!

Dave,

Is this a warm-up for some more 'Rotation of the Earth' stuff?!

[ 06-26-2004: Message edited by: Brown Dog ]

 

[Newbie]

Danger Space is the portion of the projectile's path before and after it's "zero" point where it does not rise or fall above or below the target by an amount in excess of the specified kill zone. For example, if the specified kill zone is 12 inches and the rifle is "dialed in" to hit approximately dead on at 700 meters, the Danger Space would be equal to the amount of distance on each side of the target where the bullet is no more than 12 inches above or below the target.

Edited: Sorry Brown Dog, I didn't see that you had already explained the concept before I posted my response.

[ 06-26-2004: Message edited by: Newbie_71 ]

 

[Dave King]

Brown Dog

How'd you know that???? Do I telegraph that openly??

I was out for a walk on the Appalachian Trail (AT) today thinking on this problem "Danger Space" and just might launch into a deep discussion at any moment... how about now!!

Like you state, for the military and their seemingly vertical targets there is more apparent danger space for the common shooter/rifleman. For hunters and the more horizontal targets (sorry, they're not really JUST targets but I'll call them that here for ease of discussion). I got to thinking I could put together a little program or spreadsheet that a user could calculate ballistic trajectory and also enter the targets' kill zone size and get an answer back for the Danger Space limits. Sounds like a worthy puzzle and deviation.

Newbie_71

Have we come close to actually answering your question?? If not let's finish that up and maybe continue on with this danger space thing. Thanks

 

[Newbie]

Dave King,

Do you consider "Danger Space" of much relevance at all to civilian long range shooting? Do you know if it of much significance in regards to sniping?

What I'm mostly been thinking about is which rounds will allow for the most tolerance in regards to distance approximation errors. For example, if the target is 500 yards away, what rounds will "forgive" the most in terms of how far away the approximation is. I've noticed that there are instances where a round with more actual flight time (and correspondingly more bullet drop) will actually allow for more error while still maintaining shot placement in the specified kill zone (even though this usually means you will have to crank your scope a little more) and whether or not others consider this to be as significant as total bullet drop and/or the number of click adjustments one must make on his scope.

 

[Dave King]

Newbie_71

I'll get back to you on this in a few hours. We do of course consider "danger space" when we hunt ( the use of the term "continuous danger space" could be loosely considered the MPBR term hunter typically use). We're not often concious of it when we hunt short range if there's considerable excitement but most long range guys adjust their data as the critter approaches or recedes from the hunter.


All

Here's an article on differing terms including "Cone of fire", Beaten zone" and "Danger space".
http://www.leatherneck.marines.usna.edu/images/Pubs/b2107.pdf

 

[Dave King]

Newbie_71

Your question:

"Do you consider "Danger Space" of much relevance at all to civilian long range shooting? Do you know if it of much significance in regards to sniping?"

Because most folks aren't worried about being shot (or shot at) by the critters they hunt there often isn't a tremendous amount of concern about a first round hit. That's not to say that there isn't a group of us that are first round hit hunters but we do have the luxury of making a second shot in most cases. In sniping (in the military manner) it's of considerable importance IMHO.
We have the luxury of ranging our target(s) but there is some error in the system(s). Lasers that range background objects vice the actual critter are a problem, MilDot ranging on critters of estimated size also introduces an error in range. Once the range error exceeds the danger space things get a little dicey.

For example: That 308 round at 2580fps, 175 (.498 BC) @ STP. Use a 12 inch kill zone size (two dimensional target) and we have a continuous danger space (MPBR) of 340 yards with a 290 yard zero. (Pretty good so far.) BUT move that critter to 500 yards and you now have a danger space 55 yards deep (470 to 525). Now well head out to 650 yards (my max range) and the danger space is down to 30 yards deep (635 to 665). 1000 yards and well have just under 16 yards of danger space (991 to 1007) (for comparison a military sniper would have about 46 yards of danger space for a 36" torso hit).

The error rate for laser ranging 1000 yards is +-1 yard for instrument (as stated by manufacturer I believe). Making sure we've collimated our laser and are actually ranging the critter at 1000 yards is another matter but we only have about 15 yards to play with, 7.5 in front and 7.5 behind, pretty close measurement for 1000 yards. What does this mean??? It's pretty difficult to keep this in mind when shooting and it's just a little too much info for most folks. I guess it's like walking a tight rope, we don't care what's on the sides or how far down it is as long as we stay on the rope.

Little side note: If we push that same bullet to 3150fps the 1000 yard danger space opens up to about 26 yards...this is a good sell for a magnum chambering.


"What I'm mostly been thinking about is which rounds will allow for the most tolerance in regards to distance approximation errors. For example, if the target is 500 yards away, what rounds will "forgive" the most in terms of how far away the approximation is. I've noticed that there are instances where a round with more actual flight time (and correspondingly more bullet drop) will actually allow for more error while still maintaining shot placement in the specified kill zone (even though this usually means you will have to crank your scope a little more) and whether or not others consider this to be as significant as total bullet drop and/or the number of click adjustments one must make on his scope."

For any given BC the faster you push the bullet the greater the danger space you'll have. If it's dissimilar bullets you'll need to run the numbers but no matter the muzzle speed of the lower BC bullet the greater BC bullet at lower speed (within reason) will eventually beat it out in danger space.

 

[Aussie]

Wow, this is deep and meaningful stuff here . How about a .22/250 Ackley shooting 80gn VLD's at about 3300 fps or a .243 AI , 6mm AI or 6mm/.284 shooting 95gn VLD's at 3300 - 3400 fps. BC's in the .520's . Danger space is pretty long all the way out yonder . Barrel life should be o.k. (compared to big .30 cals + anyway). Plenty of grunt for varmints to 1000yds plus.