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Login Name Post: Any difference in point of impact when using different powders?        (Topic#306589)
twisted_1in66 
54 Cal.
Posts: 1609
twisted_1in66
02-28-18 12:21 PM - Post#1671992    

    In response to Rifleman1776

The ball actually continues to drop at the same rate from the point of fire as the slower ball, meaning that with the same point of aim it takes the same amount of time to drop to the ground as the slower ball does. But it travels farther in that same amount of time. Because they both get to the same distance (point of impact) at different times, they have dropped different amounts at the same distance.

Time to target is the key here. The faster ball reaches the point of impact before the slower ball does. The faster ball doesn't drop as much as the slower ball because not enough time has elapsed to allow it to drop as much at that distance.

Twisted_1in66
Dan

 
Spence10 
Cannon
Posts: 6988
02-28-18 01:05 PM - Post#1671999    

    In response to Rifleman1776

  • Rifleman1776 Said:
'splain please: How does less time for gravity to have a pull on the ball lower the poi?


That depends on where the POI is in relation to the distance the gun is sighted for. If the gun is sighted for 100 yards, then at 100 yards a faster ball will hit the target higher, not lower, because, overall, there is less time for gravity to pull it lower.

That's not necessarily the case when the target is at a different distance than the one the gun is sighted for.

Every ball travels a looping path to the distance it's sighted for. First it climbs up and then it falls down, and that means there is a point at which it is at its highest. That point is called the Mid-Range Trajectory (MRT), and is approximately half way to the sighted distance.

In your case, if the target/POI is between the muzzle and the MRT, then the faster ball won't have time to climb so much, so the POI will be lower. So will the MRT.

Spence


 
Rifleman1776 
Cannon
Posts: 14714
Rifleman1776
02-28-18 02:55 PM - Post#1672013    

    In response to Spence10

  • Spence10 Said:
  • Rifleman1776 Said:
'splain please: How does less time for gravity to have a pull on the ball lower the poi?


That depends on where the POI is in relation to the distance the gun is sighted for. If the gun is sighted for 100 yards, then at 100 yards a faster ball will hit the target higher, not lower, because, overall, there is less time for gravity to pull it lower.

That's not necessarily the case when the target is at a different distance than the one the gun is sighted for.

Every ball travels a looping path to the distance it's sighted for. First it climbs up and then it falls down, and that means there is a point at which it is at its highest. That point is called the Mid-Range Trajectory (MRT), and is approximately half way to the sighted distance.

In your case, if the target/POI is between the muzzle and the MRT, then the faster ball won't have time to climb so much, so the POI will be lower. So will the MRT.

Spence





OK, we agree on the first part.
But that last part, not at all. The "looping" trajectory will have the ball higher than the desired poi at 100 yards. Meaning, at 50 yards it will hit higher, never lower.

 
Spence10 
Cannon
Posts: 6988
02-28-18 05:53 PM - Post#1672045    

    In response to Rifleman1776

  • Rifleman1776 Said:
The "looping" trajectory will have the ball higher than the desired poi at 100 yards.


Not true. If the rifle is sighted in for 100 yards, it will hit exactly on the X at that range with that velocity. Shoot the same ball faster, it will hit higher. Shoot it slower, it will hit lower.

  • Quote:
Meaning, at 50 yards it will hit higher, never lower.


It doesn't work that way. Faster balls travel a flatter path, the highest point of the "loop" is lower.

Spence


 
azmntman 
75 Cal.
Posts: 5700
azmntman
02-28-18 07:03 PM - Post#1672055    

    In response to Spence10

Range time to see for sure

 
Spence10 
Cannon
Posts: 6988
02-28-18 08:02 PM - Post#1672066    

    In response to azmntman

  • azmntman Said:
Range time to see for sure


All of this was worked out decades ago by people much more qualified than I. Any errors in my description of it are my errors, not that in the base of solid knowledge built up over many, many years. I won't be going to the range, been there and done that, but if anyone wants to test my description at the range I'll look forward to the report.

Spence


 
twisted_1in66 
54 Cal.
Posts: 1609
twisted_1in66
03-01-18 02:14 PM - Post#1672168    

    In response to Spence10

  • Spence10 Said:
  • Rifleman1776 Said:
The "looping" trajectory will have the ball higher than the desired poi at 100 yards.


Not true. If the rifle is sighted in for 100 yards, it will hit exactly on the X at that range with that velocity. Shoot the same ball faster, it will hit higher. Shoot it slower, it will hit lower.

  • Quote:
Meaning, at 50 yards it will hit higher, never lower.


It doesn't work that way. Faster balls travel a flatter path, the highest point of the "loop" is lower.

Spence




If you have sighted in your rifle for 100 yards with the velocity you are consistently getting, then yes it will be shoot high by usually a couple of inches or more at 50 yards. That is because you have to shoot your round ball (or bullet) in an arch to hit the point of aim at 100 yards. Typically that means you will shoot a little low at 25 yards, high at 50-yards, back down a bit at 75 yards and spot on at 100 yards. That "spot on" is actually called "point blank" because the point of impact and the point of aim are exactly the same.

Here's a chart from my ballistics program. The settings for this example are listed on the left. It's for a .490 lead ball with an initial muzzle velocity of 1900-fps fired under ideal conditions. The sight height is off slightly as my sights measure 3/16" which is 0.1875, and the program rounded that up to 0.2 but that makes a negligible difference.

I adjusted the visible part of the chart so you can see from 50-yards out to 120-yds. Notice the height of the ball at 50-yards to get to 0.0 at 100-yards traveling at 1900-fps. The ball has to travel in an arch to reach that point of aim at 100-yds.



Now here's another ballistics chart with initial muzzle velocity at 2200-fps.


Take a look at the 50-yard spot again. Notice how much lower it travels at that higher velocity to reach the same POI at 100-yards (2.4" high vs 3.1" high)? That's quite a bit less. That's because it gets there faster.

The 2200-fps shot gets there .029 of a second faster than the 1900-fps shot and that's the key. You don't have to fire as high of an arch to get to your sight-in point of aim because the ball is getting there faster and doesn't have as much time to drop. It still drops at the same rate, but it travels farther in less time and just doesn't have as much time to drop as the slower ball does before it hits the target.

This is what people often refer to as a "flatter trajectory. It's really not a good phrase for what happens, but that's what's in common use. The physical amount of drop is time-sensitive. The more time the ball is in the air, the more it's going to drop. By speeding the ball up, there is less time in the air and thus less drop at the same distance (in this case 100-yards).

Hope that helps...

Twisted_1in66
Dan



Edited by twisted_1in66 on 03-01-18 02:17 PM. Reason for edit: poor phrasing...sorry

 
smo 
70 Cal.
Posts: 4019
smo
03-02-18 08:34 AM - Post#1672289    

    In response to twisted_1in66

Thanks for the info Twisted

Here is the definition of point blank for everyone ...

Point-blank range is any distance over which the trajectory of a given projectile fired from a given weapon remains sufficiently flat that one can strike a target by firing at it directly. Point-blank range will vary by a weapon's external ballistics characteristics and target chosen. A weapon with a flatter trajectory will permit a longer maximum point-blank range for a given target size, while a larger target will allow a longer point-blank range for a given weapon.


I have always been told that the projectile crosses the intended line of sight twice....once at close range then again at the poi.

This being due to the arch in its trajectory .
In your examples above even the 1900 FPS load appears it would be point blank on a deer size target out to 120 yards.

Unless I’m totally confused....again.

Twisted, would you mind running your program for a .530 ball at 1400 FPS. Sighted at 100 yards. Thanks

I would think it would be way high at 50 and low at 25 as well...
Good Luck & Good Shootin'
Smo


 
Spence10 
Cannon
Posts: 6988
03-02-18 09:03 AM - Post#1672293    

    In response to smo

The definition I've always used for 'point blank range' is related to the MRT, mid-range trajectory, so it's a definite distance. The bullet will continue to fall after it passes the distance for which the gun is sighted in. When it has fallen as far below the line of sight as it was above it at the MRT, that's the point blank range. For example, a .535" ball at 1540 fps sighted in at 75 yards will have a MRT of 1.2" at 45 yards. When it has fallen 1.2 inches below the line of sight it will be at 86 yards, which is the point blank range for that ball at that velocity. Out to that distance the ball won't be more than 1.2" above or below the line of sight.

Spence

 
Rifleman1776 
Cannon
Posts: 14714
Rifleman1776
03-02-18 09:21 AM - Post#1672298    

    In response to twisted_1in66

  • Quote:
The "looping" trajectory will have the ball higher than the desired poi at 100 yards.




This thread is starting to sound a lot like the old "who's on first?" comedy routine.

Yes I did have a brain blip when I typed that. Meant to say "at 50" yards. I know better. Am I still in trouble.

 
Spence10 
Cannon
Posts: 6988
03-02-18 09:22 AM - Post#1672299    

    In response to smo

  • smo Said:
Twisted, would you mind running your program for a .530 ball at 1400 FPS. Sighted at 100 yards. Thanks

I would think it would be way high at 50 and low at 25 as well....


I ran it. Need to know the height of your sight, so I used the average for ML guns, .85".

25 = +1.9
50 = +3.1
75 = +2.6
100 = 0
125 = -5
150 = -12.7

Spence


 
azmntman 
75 Cal.
Posts: 5700
azmntman
03-02-18 11:02 AM - Post#1672316    

    In response to Rifleman1776

Am I still in trouble.



Are you still married?




 
smo 
70 Cal.
Posts: 4019
smo
03-02-18 12:42 PM - Post#1672326    

    In response to Spence10

Thanks you Sir

Not as bad as I thought the numbers would look with that light charge.
Good Luck & Good Shootin'
Smo


 
Samuel S. 
32 Cal.
Posts: 16
03-02-18 12:53 PM - Post#1672331    

    In response to smo

I've got a .54.

What powder charge gives you 1400 FPS?

Just trying to translate the numbers to my rifle.

Thanks!

 
smo 
70 Cal.
Posts: 4019
smo
03-02-18 12:59 PM - Post#1672332    

    In response to Samuel S.

70 grns ffg Goex.

If you google Goex Load Chart it will give you the numbers.
Good Luck & Good Shootin'
Smo


Edited by smo on 03-02-18 01:01 PM. Reason for edit: No reason given.

 
Spence10 
Cannon
Posts: 6988
03-02-18 01:29 PM - Post#1672340    

    In response to smo

  • smo Said:
If you google Goex Load Chart it will give you the numbers.


Pay attention to barrel length if they have that info available.

Spence


 
Samuel S. 
32 Cal.
Posts: 16
03-02-18 02:06 PM - Post#1672346    

    In response to smo

Thanks!

 
smo 
70 Cal.
Posts: 4019
smo
03-02-18 04:25 PM - Post#1672370    

    In response to Spence10

Does not give the barrel length .

Why would that matter? Longer barrel longer burn time?

Good Luck & Good Shootin'
Smo


Edited by smo on 03-02-18 04:27 PM. Reason for edit: No reason given.

 
Spence10 
Cannon
Posts: 6988
03-02-18 06:40 PM - Post#1672393    

    In response to smo

For the same powder charge longer barrels give a little higher velocity. Not a huge deal for ordinary shooting. Need higher velocity in a shorter barrel? A little more powder will do it.

The Lyman Black Powder Handbook 1975, .535 ball, 70 grains of 3F gives 1375 fps in a 28" barrel, 1527 fps in a 43" one.

Spence

 
smo 
70 Cal.
Posts: 4019
smo
03-02-18 09:31 PM - Post#1672432    

    In response to Spence10

Thank you again Sir
Good Luck & Good Shootin'
Smo


 
Spence10 
Cannon
Posts: 6988
03-04-18 07:41 PM - Post#1672693    

    In response to smo

  • smo Said:
Not as bad as I thought the numbers would look with that light charge.


With the ball 1.9" above line of sight at 25 yards with the gun sighted in for 100 yards, you know it crossed line of sight pretty close to the muzzle.

For a gun sighted in for 75-100 yards, the lower the velocity the loopier the trajectory, and the loopier the trajectory the closer to the muzzle the ball crosses line of sight near the muzzle.

There are only 2 times when the gun will hit exactly where your aim, exactly on the sights, where the ball crosses line of sight going up and where it crosses it going down. Another way of saying that is that every gun is sighted in, zeroed, at those two places. The one near the muzzle is called the Near Zero (NZ), the one at sighted-in range is Far Zero (FZ).

if the gun is sighted in for 75-100 yards, with average hunting charges the NZ will be 10-15 yards, but if you shoot a pretty fast ball it will be out further. If the gun is sighted in for 50 yards or less, then the NZ will also be out further even with slower charges.

It can be real handy to know where the Near Zero is. I shot the head off a very tasty grouse with a heavily loaded .54 once upon a time, because I knew my NZ was 10 yards.

Spence


 
Grumpa 
58 Cal.
Posts: 2055
03-05-18 10:13 PM - Post#1672886    

    In response to hanshi

  • hanshi Said:
I've also found that revolver/pistol bullets do the opposite by striking lower as velocity increases.



Rifles are sighted with the muzzle pointed up towards the line of sight. Handguns are sighted with the muzzle pointing downward, below the line of sight. This is to allow for the rapid rise of the handgun barrel in recoil. The, faster bullet exits the barrel before the barrel has risen as high in recoil, thus the faster bullet strikes lower on the target.

Richard/Grumpa

 
Spence10 
Cannon
Posts: 6988
03-05-18 11:50 PM - Post#1672893    

    In response to Grumpa

Take a look at this slow motion video, 73,000 frames per second, and notice the very long delay between the bullet's exiting the muzzle and the barrel beginning to rise even a little. MV is 1200 fps.

https://www.youtube.com/watch?v=7y9apnbI6GA

I used to shoot a lot of [censored] pistol, most of it pipsqueak target loads but some of it real hellers, and I never changed my sight picture between the two. Based on that experience and on several slow motion videos I've watched on the web, I have serious doubts the gun ever starts to rise before the bullet leaves the muzzle.

Spence

 
twisted_1in66 
54 Cal.
Posts: 1609
twisted_1in66
03-12-18 10:22 PM - Post#1674039    

    In response to smo

Hi smo,

I ran your .53 cal and it was only under level up to 6 yards. Then it was 2.9" high at 25-yds., 4.3" high at 50-yds, about 3.5" high at 75-yds (gives 74 and 76-yd. info), Point Blank at 100-yds as requested and then drops an inch at 105-yds and 2.2" at 110-yds. So any shot between 96-yds and 105-yds is going to impact within 1" of point of aim. I would suggest that's closer than most people can see with iron sights but it's truly only point blank at 100-yds.

In the examples I gave earlier they were all sighted in for 100-yards as was this one.
Below is the table. Notice that I put the sight height in the same as mine. The height of the sight can make a little difference and the weight of the ball can also make difference. There's a slight difference in a .53 ball at 233.3-grains and a .54 ball at 236.2-gr.



Twisted_1in66
Dan

 
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