Who knows...........

deerslayer

deerslayer

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Who knows the answer to this ? A rifle sighted in for a load which produces a velocity of lets say 3000fps, which at 100metres point of impact is 2inches high.
Now same rifle , no scope adjustments shoot a load that the velocity is now 3500 fps , where would your point of impact be?
 
My considered opinion is that it would be very close to identical. Angle of departure would be constant, all that would change would be TOF. Max rise would be greater( and further away from firing line) due to higher velocity, ultimate POI would therefore move some distance downrange.
 
Grab the Federal Ammunition Ballistics program. It's free for download and you can easily compare different ballistics of various rounds, bullet weights, etc. Not as configurable as a reloading program, but it gives you a ballpark idea.
 
All objects including bullets are affected be gravity the same way. They will both accelerate at 10 meters per second squared toward the earth. Therefore in a given amount of time both bullets will lose the same height in the same given time. Since the second bullet is traveling faster it will have less time to fall and therefore impact higher. How much higher is a function of total time to target, which will vary with the bullet drag coefficient and the atmospheric conditions of the day. The easiest way to figure it out is to use a ballistic program as was suggested. Or you could chrony it at the muzzle and again near the target and plug those speeds into a time-distance-acceleration formula.

cheers,

DC
 
Well just for kicks I punched some numbers into my program and got the following -

6.5 140 gr Sierra HPBTM
Sight +2" above the bore
Temperature 59F

6.5 140 Sierra MK @ 3000 +2.00 @ 100 = zero at 245
6.5 140 Sierra MK @ 3500 +2.00 @ 100 = zero at 300

6.5 140 Sierra MK @ 3500 +1.25 @ 100 = zero at 245
 
I did the same two hypothetical loads with a .270 - 100 gr.
with bullets with a BC of .245.

The difference at 100 yards between 3000 fps and 3500 fps
with otherwise identical rounds sighted the same way is that ( with
the 3000 fps round, sighted-in at 2" high at 100 yards ) the 3500 fps round will theoretically print 3/4" lower, at only 1-1/4" high ... (less bullet rise)


Expressed another way, the 3000 fps round will be dead-on at 210 yards, if sighted at 2" high at 100, while the 3500 fps round will be dead-on at 251 yards with a 2" high at 100 yard sighting.

Sorry, inches, feet and yards for me ... no calculations for the same data at 100 metres.
 
I was at the range with my 243 ,which is sighted in for 95gr bullets @ approx. 3000fps. I shot two rounds of 55gr bullets @ 3900fps my impact was about 6in high at 100meters , 95 gr hit 2in high at 100meters. Now if you used the same grain of bullet but change velocity the faster bullet should impact the target lower than the slower, tryed using the rem shoot prg , but prg always adjusts scope.The reason I ask is that if I load 140gr bullets but use different powders I should be able to tell which rounds are faster by point of impact on the target.
 
Well looking at the point of impact doesn't give you the whole picture. The barrel harmonics are going to affect where the bullet hits as well as the velocity.

The barrel is bouncing around under the force of the rapidly increasing pressure, and the point where it hits is going to be affected by the position of the barrel as the bullet leaves the muzzle. If the muzzle happens to be in a lower position when your fast bullet exits, and the upper position when the slower bullet exits, they will have similar points of impact.

Generally speaking though, if your rifle is sighted for the slower load, and you don't change the adjustment on the scope to fire the faster load, the faster load will hit the paper higher. The barrel is at the same angle in relation to the ground, and the faster bullet of the same weight has less time to be affected by gravity.
 
It depends on the gun only way to find out load and shoot. I had a similar situation I had loaded some 30-06 loads with a lee scoop. and later when I got a proper powder scale made up a more powerfull load. The first load cronied at 2600 fps. the next load at 2900 fps. I had a few of the 2600 fps loadfs left after I had sighted in my scope for the 2900 fps. loads. As I wasn't going to use the 2600 as my hunting load I decided to shoot them off to recover the brass. to my amazment they printed 2" higher than my 2900 fps loads. As the barrel goes through a sine wave after the load is fired the exact position of the end of the barrel when the bullet exits plays a big part in where the bullet impact will be. If the bullet leaves the barrel when at the top of a wave it will be higher than if it exits on a bottom of a wave..
 
You wont know till you shoot it. It may hit the same, up, down, left or right or anywhere between. Nothing is a given when dealing with barrel harmonics and vibration.
 
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