Why do low velocities sometimes shoot high

[walkswithsticks]

As a cast bullet shooter, I quite often notice point of impact being a quite bit higher when using mild cast bullet loads.
 
A recent load in particular out of a 10" Contender barrel in 32/20 shoots about 12" high at 75 yards.  I am using 3.5 gr of HP-38 behind a 115 gr RNFP bullet cast from Wheel Weights.
 
Last year, I was shooting an old Savage Model 99 with mild loads of Unique and cast bullets that shot 6" higher at 50 yards than jacketed bullets.
 
The darned thing seems to happen in long and short barrels alike, but it is especilly irritating in the Contenders as TC has had taller front sight blades on back order for six months with no promise on the horizon.  I have tried to win auctions for the long base micrometer type rear sights, but those things end up being fairly pricey.
 
Any thoughts on why this happens, and any good solutions?
 
 

[kynardsj]

This is just my opinion and not based on any scientific facts. I have noticed the same thing for years and my conclusion is that when you fire a round you obviously have recoil. Recoil lifts the barrel. A faster load exits the barrel quicker than a slower one. The barrel has a very small amount of time to rise just a bit higher with a slower bullet before it exits. If I'm wrong I hope someone with more knowledge of this enlightens me too.

[336SC]

Exactly what kynardsj said!  More barrel time for the slower loads to react to recoil.  Certainly not chiseled in stone but I have observed
the same thing with my loads.  Sometimes you get fooled however. 
336SC

[Hopalong7]

     You guys are dead on....this is especially true when you have a lower velocity AND a heavier recoiling round.  For instance when I switch from a "medium" loaded 250gr 'er up to a "little more than medium" loaded 310gr'er in my 45Colt Blackhawk.  The POI goes way up....so much so that I had to install a taller front sight .  Yep!
Walt

[Clodhopper]

I noticed the same thing when shooting .44 Specials in my Ruger Super Blackhawk Bisley.  Couldn't adjust my rear sight down far enough to compensate so just had to shoot a few inches low.  Lots of fun though!

[jmohme]

I don't think that recoil is the issue here.
Correct me if I am wrong, but i believe that recoil does not begin until after the bullet exits the barrel.

[kynardsj]

Recoil begins as soon as the primer is hit and the powder ignites and starts pushing the bullet. Action - reaction, that sort of thing.

[Flash]

Recoil begins as soon as the primer is hit and the powder ignites and starts pushing the bullet. Action - reaction, that sort of thing.

Correct but the force of the cartridge will move the bullet exponentially faster due to the weight difference of the bullet and the gun. The bullet is actually out of a handgun barrel before the recoil begins to move the handgun. The average semi automatic handgun weighs 14,000 grains with many being heavier. If the gun recoiled at the speed that the bullet traveled, your hand would be ripped off and your handgun would be imbedded in your forehead.

[sr sawyer]

Flash,
 
For your theory to be viable the bullet would have to equal or exceed the weight of the gun.  Newtons "proven" law states that for every action there is a reaction. 
 
To say recoil does not begin until the bullet leaves the muzzle defies this law.  Recoil begins immediately upon the bullets first movement from the loaded round.  Bullet weight in relation to firearm weight decides exactly how much recoil is recorded when a bullet is fired.
 
Ken

[Flash]

Flash,
 
For your theory to be viable the bullet would have to equal or exceed the weight of the gun.  Newtons "proven" law states that for every action there is a reaction. 
 
To say recoil does not begin until the bullet leaves the muzzle defies this law.  Recoil begins immediately upon the bullets first movement from the loaded round.  Bullet weight in relation to firearm weight decides exactly how much recoil is recorded when a bullet is fired.
 
Ken

Ken, that is why I said correct. I never claimed to explain a theory, I simply stated that the speed of the bullet is far greater than the reaction of the gun to the recoil. Sure they both start at the same time but the movement of the gun is much slower than the bullet, allowing the bullet to travel a great distance before the recoil actually moves the gun.
http://blog.hsoi.com/2011/12/13/9mm-vs-40-vs-45-a-recoil-comparison-in-slow-motion/
http://www.youtube.com/watch?v=otpFNL3yem4

[ralfus]

Recoil begins as soon as the primer is hit and the powder ignites and starts pushing the bullet. Action - reaction, that sort of thing.

The bullet is actually out of a handgun barrel before the recoil begins to move the handgun.

Flash, your own video link above shows the muzzle moving before the bullet leaves the barrel. Look at the front sight's position relative to the edge of the movie.

[streak]

I always look at it as simply too much dwell time in the barrel!
 Exactly what kynards stated!

[mechanic]

If you want to see it magnified a bit, try a 32" barrel 45-70
 
Ben

[Flash]

Recoil begins as soon as the primer is hit and the powder ignites and starts pushing the bullet. Action - reaction, that sort of thing.

The bullet is actually out of a handgun barrel before the recoil begins to move the handgun.

Flash, your own video link above shows the muzzle moving before the bullet leaves the barrel. Look at the front sight's position relative to the edge of the movie.

Do you mind sharing which direction your eyes see the barrel moving? I see the barrel moving back about 1/16".
"Back" doesn't cause "up"

[ralfus]

Recoil begins as soon as the primer is hit and the powder ignites and starts pushing the bullet. Action - reaction, that sort of thing.

The bullet is actually out of a handgun barrel before the recoil begins to move the handgun.

Flash, your own video link above shows the muzzle moving before the bullet leaves the barrel. Look at the front sight's position relative to the edge of the movie.

Do you mind sharing which direction your eyes see the barrel moving? I see the barrel moving back about 1/16".
"Back" doesn't cause "up"

Thank you for agreeing that the handgun moves before the bullet leaves the muzzle. No personal offense intended. Dwell time while the bullet is in a longer barrel also has an effect such as in a 10" TC.
This video shows it a bit better:
http://www.youtube.com/watch?v=Um9Eos9bJDk&feature=relmfu


This one also (at around 0:09):
http://www.youtube.com/watch?v=vloe_60s_dk&feature=relmfu

[Flash]

Yes, there's no denying the gun moves at the same time as the bullet but I believe the question was whether or not, the bullet impact could be raised due to the recoil of the gun and the answer is no. The bullet is long gone from the barrel, before the gun begins to move far enough, or in a direction to affect it's impact.

[streak]

Ah yes me lads!
 But once the gun moves then the bullets trajectory is affected and the longer the bullet dwells in the barrel due to slower velocity the barrel will be tending to rise and thus the bullet will strike at a higher position then it would at a higher velocity!
Let us not forget Einstein`s Theory!!!
Another example of this if you take a say a 44 magnum and use essentially the same powder load behind a 180 gr bullet as opposed to 250 gr bullet and take a target
say at 50 yards and shoot the 250 gr bullet will shoot higher on the target as opposed to the 180 gr bullet simply because of the heavier bullet traveling at a slower velocity down the barrel as the barrel is already in motion, ever so slightly that might be, it is still in motion and the heavier bullet leaves the barrel
at a slower time than is experienced by the 180 gr bullet!

[Flash]

Ah yes me lads!
 But once the gun moves then the bullets trajectory is affected and the longer the bullet dwells in the barrel due to slower velocity the barrel will be tending to rise and thus the bullet will strike at a higher position then it would at a higher velocity!
Let us not forget Einstein`s Theory!!!
Another example of this if you take a say a 44 magnum and use essentially the same powder load behind a 180 gr bullet as opposed to 250 gr bullet and take a target
say at 50 yards and shoot the 250 gr bullet will shoot higher on the target as opposed to the 180 gr bullet simply because of the heavier bullet traveling at a slower velocity down the barrel as the barrel is already in motion, ever so slightly that might be, it is still in motion and the heavier bullet leaves the barrel
at a slower time than is experienced by the 180 gr bullet!

What mathematical figures do you have to substantiate this other than, "Let's say a"
At 800 feet per second (550 mph), a bullet will travel down a 4" barrel at 1/2400 of a second.
 
I got this off another forum.
 
 Okay, this is my first post on this forum, but since I'm a physics student, I tought I could sort this out.

Both Mark38 and Peetzakilla have some true points. You're just looking at it starting from other laws. According to the third law of dynamics which Peetzakilla used in his explenation, the momentum will stay the same in the whole system. This however is caused by the actions of the gas Mark38 explained. The only point he got wrong is that the bullet isn't part of the gun, so when the gas pushes in all directions, it pushes against the bottom of the casing and the bullet. Since the bullet has friction, a part of the pressure against the casing is compensated for by the friction of the bullet.

All of the force used to accelerate the bullet will be felt as recoil too. As the gun weighs roughly a hundredfold of the bullet, the weapon will go only one hundreth of the speed of the bullet in recoil. So while the bullet is acceleration from 0 m/s to it's v0, the "recoilspeed" of the gun will be in direct proportion to the speed of the bullet at that particular moment.

And now we're getting to the point. If we look at the generated recoil energy, we see that the part caused while the bullet is in the barrel is only 1/3th of the total recoil energy. The other parts caused by burning gasses when the bullet has exited.

So to sum it up, if someone would really want it, I want to calculate the rotational speed of a recoiling weapon. However, considering the facts I mentioned above, I'm pretty sure it would be fairly pointless, and it would most likely be in the range of some millimeters without any noticable effect in practical applications.

9-ball

[streak]

Well Flash it doesn`t take a physics major to sort this out!
I would simply go out and do a shooting test of my own and see the results.
As mechanic mentioned earlier a long barrel 45-70 really illustrates the point  with a high velocity load and a low velocity load using the same grain bullet!
 

[billythekid55]

A gunsmith friend of mine explained this as 'barrel time'. I experienced it shooting the same weight .38 special and .357 factory bullets. The .38 stays in the barrel longer and the recoil has an effect on it. The 'smith' told me shooting .44 special out of a handgun sighted in with .44 magnum made a difference of almost a foot at 25 yards. In my experience, shooting the slower .38 special would be 6" higher at 25 yards than full house .357. This was with a bull barrel. If I shot the same test out of a lighter octagonal barrel, the distance was more than 8".
 
Billy

[Flash]

Well Flash it doesn`t take a physics major to sort this out!
I would simply go out and do a shooting test of my own and see the results.
As mechanic mentioned earlier a long barrel 45-70 really illustrates the point  with a high velocity load and a low velocity load using the same grain bullet!

That's the whole reason for my arguement........I don't experience it. Of course my velocity spread isn't ever that great because i never load anything "hot".