Slower bullets shooting higher

Two shots fired with my 308 a few years back. One with a 155 Amax and the other 168gr Amax both loaded to the same speed. Although there is a big difference in recoil the POI is the same. This rifle has been balanced so that the COG is on centre bore. Forward-back position of COG is not important but the up-down and left right position is. Recoil does not change launch angle... or much less. Rifle will torque and move in line with the centre bore. Target backing is a rubber mat.

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edi
 
MRP said:
Took my 44 Rossi ranch hand with a full length stock out shooting. I put a small reflex sight on it, old people with bad eyes need some help. First, I shot my 240gr hard cast traveling at 900 fps zeroed it at 75 ft. Then I tried shooting some jacketed bullets traveling at 1650 fps and, thay shot 4 in lower? Now I know nothing in shooting and reloading is an exact science but at 75 ft I thought they would be close. But thinking the faster bullet should still be a bit higher, not 4," lower. So just for fun I dialed in the jacketed bullets at 75 ft, then tried the hard cast again, same thing. Slower bullets shoot 4" higher. Did the government repeal the law of gravitys affecting lead? I've heard about this sort of thing but never experienced it in 50 years of reloading and shooting.
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It's a different arc due to the velocity difference. higher velocity equals flatter trajectory and larger rang at which you can "point-blank" aim.

For instance, you can sight a high-powered hunting rifle in 3" high at 100m, and you'll be in the kill zone anywhere from 50m to 250m without having to hold off or adjust your scope.

Slower bullets have a shorter arc so they might hit higher at 100, but they're waaaay lower at 200, whereas the faster round will not have dropped as far.

Sometimes the bullet is still climbing at 100m, whereas a slower load might already be falling by 100m ... you get the idea.

Hope that makes sense.
 
Canuck65 said:
It's a different arc due to the velocity difference. higher velocity equals flatter trajectory and larger rang at which you can "point-blank" aim.

For instance, you can sight a high-powered hunting rifle in 3" high at 100m, and you'll be in the kill zone anywhere from 50m to 250m without having to hold off or adjust your scope.

Slower bullets have a shorter arc so they might hit higher at 100, but they're waaaay lower at 200, whereas the faster round will not have dropped as far.

Sometimes the bullet is still climbing at 100m, whereas a slower load might already be falling by 100m ... you get the idea.

Hope that makes sense.
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No, it doesn't make sense it's irrelevant
 
Come to think of it my 44 40 loads must be doing that too since my 1030 fps loads and my 1680 fps loads arrive at the same place at 100 metres which I thought was strange. And they werenot so far different at 50 that I noticed. I think it must be that the aim changes after the triggerispulled due to recoil timing or maybe vibration, the trigger pull could affect it
 
osborne said:
Basically the slower bullet remains in the barrel longer allowing the upward recoil of gun and therefore increased barrel angle to drive the point of impact higher. If you held the rifle tighter or strapped it to a sled you would see a reduced effect.
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That's absolutely it. I shoot black powder target rifles and see that all the time. The slower the bullet and the heavier the recoil the more pronounced the effect. When shooting prone I get significantly different elevation depending on how hard I grip the rifle. This is only noticed at short ranges, maybe up to 300 yards or so. After that the ballistics of the slow moving projectiles starts to erase the effect.

Chris.
 
Thanks guys. That has to be it, longer time in the barrel in relation to the recoil. This would also explain why subsonic loads poi can varry so much depending on shooting position. My 3030 cast and trail boss loads changed a lot from bags to freehand, with iron sights and old eyes I thought it was just me.
 
struff55 said:
the issue is 75 ft zero the faster bullet has not reached its highest rising point of trajectory you have to compare apple to apple not oranges to apples
the faster bullet has a flatter trajectory
defiantly some interesting theories šŸ˜Š
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There is no rising point of trajectory. The bullet only drops after it leaves the bore. It never rises above the bore. Sights are off set to intersect the bore line.
 
But the bullet NEVER rises... it is incorrect to suggest it does as some newbies may end up believing that.
 
guntech said:
But the bullet NEVER rises... it is incorrect to suggest it does as some newbies may end up believing that.
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Yes true, but since the rifle becomes very dynamic when the shot is being fired the bore and direction of aim can change before the bullet leaves the barrel. So the bullet could rise above the initial bore direction. Won't raise above the direction/aim at the time of the bullet leaving the muzzle.
edi
 
I was just recently shooting some surplus NATO 7.62 ammo and was impressed both by the lighter recoil and higher point of impact over the commercial hunting products I sighted in with.
 
I've seen that effect before.

At shorter distances the heavier bullet will print higher. Like others I've heard it linked to the slower velocity and therefore longer time of bullet in barrel. The net effect is that the recoil raises the muzzle slightly and causes the heavier bullet to print higher.

In heavier recoiling pistols the effect seems more noticeable.
 
Perhaps the point of my comment in post #33 isn't as clear as I thought it would be. I thought that rifle enthusiasts would know that military 7.62 x 45 ammunition is loaded to generate lower chamber pressures than those often found in commercial game rounds (and incidentally less felt recoil). With my scope zeroed to big game rounds, that plus what is likely to be a lighter weight ball style bullet yields a different trajectory than over the counter stuff does, altering the point of impact even at 100m distances. What I saw averaged out to a noticeable average of about 2 cm or 3/4 of an inch. And the mil surp stuff is pleasanter to shoot, especially over the really heavy moose loads.
 
porpoise said:
I had light loads in my 270 do that, otherwise every light load in every rifle I tried landed lower. Including pistol rounds. Don't know about handguns
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Dwell time, lower velocity results in the bullet remaining in the barrel longer, therefore the recoil of the firearm has more time to act in elevating the muzzle. The old .38 Special the RCMP used exacerbated this by having a 5 inch barrel. I believe it was Massad Ayoob who wrote of an experiment where a revolver was mounted in a vise and the sights aligned on target, a line was passed through the firing pin hole, through the center of the barrel out to the target. It was found the barrel centerline was below the 'point of aim' to compensate for the muzzle flip vs velocity.
 

EJG said:
Yes true, but since the rifle becomes very dynamic when the shot is being fired the bore and direction of aim can change before the bullet leaves the barrel. So the bullet could rise above the initial bore direction. Won't raise above the direction/aim at the time of the bullet leaving the muzzle.
edi
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Yes let's bring back a red herring to reconfuse things
 
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