I fired my Remington 581 to sight it in at 80 yards last weekend and then fired at 60, 40 ,and 20 yards to know where my point of aim would have to be to hit the silhouette targets at their respective ranges. I tried running a ballistics chart to see how close it would be to my actual shooting. There was something weird about the targets compared to the trajectory that was computed. When I drew out the rise from point of aim on a short line (using inches for yards of range and plotting the bullet path from my targets in inches I discovered that there was more rise from 40 to 60 yards than there was from 20 to 40 yards. The bullet was climbing faster from 40 to 60 than it was from 20 to 40 yards. That is impossible but the targets don't lie.

The only thing I could think of is that the distance corresponds to the transonic velocity. Perhaps the buffeting is turning the bullets trajectory up so it changes its flight path.

Is this possible? am I not thinking of something?

it crosses line of sight at what range?? 15-25 maybe has something to do with it??

crossing the line of sight has little to do with the climbing. Unless something is giving extra pushes to the bullet during its flight, the bullet's way of climbing can only decrease during the flight.

Or the bullet needs more time to stabilize (I've been told that a .303 British also need about 300 yards before the flight stabilizes, at shorter distances it's still making a spiral), or you have a kind of mirage winds pushing the bullet upwards (but then at such small distances???), or Suz was doing some weird hocus-pocus dances while you were shooting...

Hmm, anti gravity .22 and super speeding .357M.
What else you got inside your sleeve Paul

Green with jealousy
Gelan

PaulS, you didn't say how many rounds were fired or what the ammo type was nor which group was shot with a colder or warmer barrel. There is variation in bullet POI compared to POA. Depending on the standard deviation or circular error probability (CEP), the POI of the group shot a 40 yards could have been lower than normal causing your anomaly.

I had a rocket project in a science class where a single rocket motor propelled the rocket higher than when two of the same rocket motors where used because the standard deviation of thrust variation was so large that it was possible to have a rocket motor with more than double the thrust thrust of rocket motors that were below average. (freaking prof gave me a D for figuring that out)

The targets were all shot from a cold barrel.
I was using Winchester "Wildcat" ammo
The muzzle velocity is 1208.
It crosses the transonic region at about 40 yards.
My scope is mounted at 1.378" (center to center from the bore)
Impacts on the targets are:
20 yds; +0.75
40 yds; +1.125
60 yds; +1.875
80 yds; 0.0

Fired from a bench with the point of aim the center of a 1" dot. My scope makes it an easy shot and I am sure of the point of aim.

From 20 to 40 I see a 3/8" rise and from 40 to 60 I see a 3/4" rise.
The only thing I can think of is that the transition to subsonic is pushing the bullet up as the center of pressure changes. (but I am grasping at straws here.)

Have you repeated the test enough times to be statistically significant?

UH OH...Slim's going all scientific on us here.

All fired from the same point with the center of the targets at the same level?

i.e. - If you run a laser down the bore to the 80 yard dot would the 20-40+- and 60 yard dots be on the laser line too?

If your angle of fire changed between distances it would affect your percieved drop too.

The range is on a slight uphill grade. The targets are mounted in the same position on my target stand approximately four feet off the ground. I am shooting from a bench that is 36 inches high with a rest that is 8 inches high.

How much would that affect my shot placement? The overall angle of the barrel would be less at 80 yards than at 20 yards. No, the targets would not line up with a laser. That doesn't change the fact that the trajectory doesn't come close to matching anything from all eight of my ballistics program no matter what parameters I change.

The next time I am at the range I will see if I can shoot a statistically acceptable number of runs. I could even attempt to adjust the targets so they would line up with a laser.

Dawgdad,
Since my sight adjustment is not changing and it is sighted to zero at 80 yards and I am shooting to the same point of aim with each change in range are we really dealing with a change in angle large enough to go 3/8" high in a 20 yard span?

PaulS wrote:

the trajectory doesn't come close to matching anything from all eight of my ballistics program no matter what parameters I change.

There's your problem. Confucius says a man with more than one watch doesn't know what time it is. The same must apply to ballistics program.

PaulS wrote:

The range is on a slight uphill grade.

This could be the problem.

3/8th of an inch...not a problem its still hitting where it is hitting, YOU KNOW where it is hitting...no problem.
this is why we go to the range or pattern board. SO WE KNOW.
What time is it??? heck some weeks I dont even know what plurry DAY it is!!!

Paul your over thinking it.
Aim rifle, pull trigger, pick up rabbit.

What it does in between leavIng the barrel and hItting the rabbit isnt that important as long as it hits the rabbit.
It does however keep the forum ticking over on these cold winter nights.

Shooting up or down the hill, both will give you a higher POI as expected, but: on this short distances? And going faster upwards further away from the muzzle???

But I have to admit: when I should see something like that, I would blame my eyes or my shooting...