Fact or myth?

Best example of how much rifle movement and its direction is before the bullet leaves the barrel is hot gunning the same rifle in a prone match. The same 30 caliber magnum match rifle used by 4 people will easily have a 1.5 MOA spread in sight settings for a given range zero. That's because the rifle moves differently with each shooter 'cause they don't all hold it exactly the same way.

No, it ain't how folks look through sights. Light from the target goes through the sights the same way for everybody. That light and those sights do not know who's on the rifle to shoot it; they perform exactly the same way for each person.
 
1.5 MOA? wow that is a lot. I am not disputing you, your level of experience is far beyond mine. But I was thinking this effect would be a .5 MOA kind of effect.

So Bart, how much effect would I see between shooting with a sandbag under the forestock, versus in a seated position using a sling ?... The sling certainly pulls down on the forestock, at least 5 to 10 lbs of pull down I would estimate. If I sight in my rifle at 200 yards at a bench using a sandbag, am I screwed if I use my sling to make a 200 yard shot in the field?
 
Highly recommend using a sling for 200 yards. If you sling up the same every time your hold will be consistent for you and your groups will show it. I got so used to a sling that when I was shooting small bore I felt naked without it.
 
Back in the police revolver days, the state police in XXXXXXXX were issued .38 Special +P+ ammunition to replace their old 158 grain lead bullet loads. They soon found out at the range that their shots were going well below the center-of-mass on the silhouette targets they were using. The reason, of course, was the lessened barrel time with the lighter and faster bullets.

But their firearms instructor was not a ballistician and had invented his own theory to explain the situation. He solemnly informed the troopers that the new ammunition was designed to hit the miscreant in the (censored) and leave him less inclined to evil ways. Incredibly, the cops believed it and the whole thing was a minor kerfluffle for a few days in the cop shops until someone in the know got things straightened out. Fortunately, the business never reached the newspapers - or the civil rights groups.

Jim
 
With my .44Magnum revolver, I have to raise the rear sight nearly a turn and a half when I go from 240 grain bullets to 180 grain bullets.

I also believe that there is measureable movement before the primer goes off from the reaction of the hammer falling. This may be one of the reasons a good BR rifle has a short striker throw. It's not just fast lock time, it's minimum gun movement during the striker fall.
The forces involved with accelerating the bullet are very big, thousands of pounds, and it's very hard for the human body to significantly interfere with that force, however, the forces involved with the firing mechanism are small and a firm verses limp hold has a large infuence in gun reaction to this movement.
Also, the sudden release of trigger pressure when the sear releases can cause a shift in gun position during lock time. I found this out when shooting a flintlock pistol, even though I wasn't flinching, I had a lot of shots go low. It turned out that the pressure on the trigger was part of my hold and when the trigger broke, the release of that pressure allowed the gun to drop as the chain of events leading to ignition occured. When I concentrated on holding the pistol firmly with my middle, ring, and little fingers, using the index finger only to pull the trigger and not to hold the gun, the problem went away and I started shooting better scores.
 
Bart B, Most prone matches are also govern by set of rules as to how rifle is shot and I sure don't disagree that someone shooting a rifle that they haven't sight-in for a given range zero will vary.
 
Wow. I've learned a lot from your posts. Thanks, to each of you. I had assumed that a consistent hold was purely to shape the shooter's habits but I see now that it affects the physics involved within the firearm too.
 
Basic physics tells us recoil begins as soon as the gases start expanding. The mass of the rifle is significantly larger than the mass of the bullet, so the bullet leaves quickly with a much higher velocity than the rifle moves backward. The high mass of the rifle being driven against your body is what is felt as recoil. Heavier rifles with similar action types and similar barrel lengths will typically recoil less since there is more mass to move. Theoretically, the bullet would get the benefit of that in speed, but I am guessing that is a negligable increase.
 
Most prone matches are also govern by set of rules as to how rifle is shot and I sure don't disagree that someone shooting a rifle that they haven't sight-in for a given range zero will vary.
Click to expand...
Having shot a dozen or more long range matches on 4-man teams all using the same rifle that was previously zeroed for each shooter, I can attest that each person's zero was 1/2 to 1 moa or thereabouts spread across them. Both on metallic and scope sights. Most of the difference was in windage; not much in elevation. But the sight in zeros fired a week or two before the match ere still good during the match.
 
That is a lot more variation than I would have thought. I think I will stop sighting-in rifles for other people, I might be doing more harm than good.
 
OK, a few points:
* Yes, recoil begins as soon as the shot is fired (that whole equal and opposite thing that Newton guy came up with). The momentum (mass X velocity) of the bullet = the momentum of the rifle. This is due to the law of conservation of energy.

* Where it gets a little goofy is that the kinetic energy (1/2 mass X velocity squared) of the bullet and the kinetic energy of the rifle become grossly different, otherwise recoil would cripple you.

* The majority of recoil is from the so-called "jet effect", i.e. the high-velocity gases hitting the stationary atmosphere and pushing the firearm backwards, which occurs after the bullet leaves the muzzle. This is why a 30-30 seems to kick so much less than a 30-06 firing the same weight bullet: the portion of recoil from momentum is only 15% higher, but the portion of recoil from the jet effect is much higher (50% higher pressure gases, and 60% more of it).
 
My experience shows a rifle sighted in by a right handed shooter from a bench will have a zero about one moa left than if sighted in from standing or offhand. This is for a .308 Win.
 
Last edited:
A gun (any gun) recoils around its own center of gravity and around the center of gravity of the gun-shooter system, where the parts of the shooter that touch/hold the gun become part of that center of gravity calculation. So the way the shooter holds the gun does affect the way it recoils and consequently the direction of the bullet. Firing the same rifle with the same sight setting, a left-handed rifle shooter will see his bullets strike a different place than a right-handed shooter firing the same rifle or a portly shooter will find bullets striking a different place than a slender shooter. That is why folks in the know say that each individual must sight his rifle for himself. Someone else can get close, but that might not be good enough.

Vibration can also have an effect, as can resting the gun on a solid object. For example, a handgun sighted in with the barrel or butt resting on a bench will not shoot to the same place when hand held.

Jim
 
Scorch said:
* The majority of recoil is from the so-called "jet effect", i.e. the high-velocity gases hitting the stationary atmosphere and pushing the firearm backwards, which occurs after the bullet leaves the muzzle. This is why a 30-30 seems to kick so much less than a 30-06 firing the same weight bullet: the portion of recoil from momentum is only 15% higher, but the portion of recoil from the jet effect is much higher (50% higher pressure gases, and 60% more of it).
Click to expand...

Numbers Taken from QuickLoad

Cartridge, Bullet Weight, Powder, Recoil at muzzle exit (ft/lbs), Recoil after Gas Effect (ft/lbs)

.25-06, 120gr RL19 8.44 15.27
.204 32gr Win748 1.44 2.80
.22-250 35gr Win748 2.51 4.47
.30-06 180gr Ramshot Hunter 15.02 24.07
.30-30 180gr Accurate 2495 7.73 10.59

The portion of recoil attributed to "Gas After-effect" is significant but doesn't typically constitute a majority (over 50%). The gas effect alone does add almost as much recoil to the 30-06 as the TOTAL combined recoil of the 30-30 though.
 
The gasses that push the bullet have the same mass as the powder that generated them.
When the powder charge comes close to outweighing the bullet, like in a .22-250 or other hypervelocity varmint rounds, the powder gasses generate the lion's share of the recoil.
In cartridges where the bullet is many times heavier than the powder charge, smokeless .45-70 loads, .22 long rifle, etc, the bullet is responsible for the lion's share of the recoil.

A .30-30 has a approximately 30 grain powder charge pushing a 150 grain bullet, so the powder charge's contribution is not as great as a cartridge where a 50 grain powder charge is pushing the same bullet to a much higher velocity.

A .22 long rifle standard velocity has about 1 grain of powder pushing a 40 grain bullet, almost all the recoil is from accelerating the bullet.

Blanks actually do kick a little.
 
B.L.E. said:
When the powder charge comes close to outweighing the bullet, like in a .22-250 or other hypervelocity varmint rounds, the powder gasses generate the lion's share of the recoil.
Click to expand...

The thing is, a lot of those gases (anywhere from approximately 50-66%) don't accelerate with the bullet, but what gases do go down the tube eventually end up going A LOT faster than the bullet, as soon as the bullet "uncorks" the barrel.

However, see my list above. The percentages of recoil contributed by the gases are about the same for hyper-velocity rounds with light bullets and more standard cartridges with heavier bullets.

That 22-250 35gr bullet has a MV over 4,400fps and the powder charge is HEAVIER than the bullet but the gases only contribute 43% of the recoil. In the .30-06 example, the powder contributes 37% of recoil.
 
Great statement:
A gun (any gun) recoils around its own center of gravity and around the center of gravity of the gun-shooter system, where the parts of the shooter that touch/hold the gun become part of that center of gravity calculation.
Click to expand...
Which is why .22 long rifle free pistols have their grips designed to put the barrel axis aligned with the shooting arm axis as much as possible so recoil during barrel time will least effect the bullet's exit axis compared to the sight axis when the firing pin struck the case.
 
80 grains of ffg black powder by itself in my muzzleloading 12 gauge creates a noticeable recoil, and is a great way to kill a wasp nest on the rafters of a barn. Hold the muzzle about a foot away from the nest and pull the trigger and BOOM!!! the nest is completely gone along with the wasps.
I imagine a 7.62 Nato blank would have the same effect.
 
You must log in or register to reply here.
Back
Top