Physics of shooting a rifle

[tangolima]

The force that compresses the spring also asserts on the sleeve (action and reaction). It will accelerate backward as the spring is being compressed (F=m x a). The sleeve can't possibly be stationary.

Heavy sleeve/soft spring = slow sleeve/a lot compression. Light sleeve/stiff spring = fast sleeve/little compression. It is also possible that the spring bottoms out during recoil. It becomes a solid steel disc. That may well be the Benelli trick. The sleeve aquires the same speed of the receiver and is further accelerated by the compressed spring.

I think qualitatively we are taking about the same thing. Difference is in the quantities. The video clips are good. But they could be a bit over simplified for marketing purposes.

-TL

Sent from my SM-N960U using Tapatalk

[JohnKSa]

The sleeve can't possibly be stationary.

Yes, of course, there will be some acceleration on the sleeve before the acceleration cycle of recoil finishes because the spring is very stiff, but the point is that the sleeve is propelled by the spring, not by the impulse of recoil. It's absolutely clear in the videos that initially the sleeve stays more or less still (note that I've been saying "more or less still" repeatedly throughout this exchange) during the first part of recoil which is not how a momentum/recoil operated system works.

In a momentum/recoil operated system, the moving parts get all their kinetic energy before the bullet leaves the barrel from conservation of momentum. In an inertia operated system, the moving parts get their kinetic energy mostly after the bullet leaves the barrel from the potential energy of a spring. It's a fundamental difference and it is clearly visible in the videos.

If the gun were recoil operated, the bolt would move with the gun as soon as recoil begins and then continue rearward when the shooter's shoulder decelerated the gun. Instead, it does not move with the gun in recoil, it initially stays more or less still and that inertia compresses a spring which then drives the bolt rearward when it decompresses.

The video clips are good. But they could be a bit over simplified for marketing purposes.

They actually show the system in operation. No way to oversimplify that--you can see what is actually happening as the system operates.

The explanation Benelli gives (and the one I've given) is consistent with physics and with what can be seen visually in the videos. There's no need to try to cast about to come up with some other explanation for how it works--we can see how it works in the video and we can hear how it works from the people who designed the system and worked out the physics to make everything function properly.

I think qualitatively we are taking about the same thing. Difference is in the quantities.

I think that if you can convince Benelli they don't know how their system works, you may be onto something. Until then...

[tangolima]

Ok John. Let's set this aside and move on to something else, shall we? Thanks.

-TL

Sent from my SM-N960U using Tapatalk

[tangolima]

Originally Posted by tangolima

When I first started handloading (I prefer that to reloading), I had a mentor. He quite liked using slower powders for pistols. The recoil is milder. Instead of snappy shove, it would be a gentler push, so he told me. So I started with just that, slower burning powders.

However I found it was quite the opposite. The recoil with faster powders, similar bullets and MVs of course, is actually more agreeable.

How so?

-TL

Sent from my SM-N960U using Tapatalk

I'm answering my own question. Hopefully the discussion can be restarted.

The recoil follows the principle of conservation of momentum. The momentum comes from the projectile and the gas existing the muzzle. The mass of the gas equals the powder charge. The speed of gas is generally higher than the projectile, so the gas' momentum is significant part of the equation.

Slower powder requires higher charge for the same MV. It has flatter pressure curve, which often leads to higher muzzle pressure. The gas exits at higher speed as result. That's why slower powder tends to have more recoil force, louder report, and more visible muzzle flash. True that the peak pressure is lower than faster powder, but human body most certainly can't tell the difference for events all happen within a minisecond or two.

Actually I managed to use this mechanism to improve one of my loads. I experimented with .22TCM9R. Found a conversion upper for Glock 23. The recoil spring is very soft, and yet it doesn't cycle reliably, even when the load is maxed with bullseye. The MV is crazily high. But with the light 40gr bullet, the momentum is just not enough. I switched to Ramshot enforcer, and it worked. It is loud with big ball of fire. Basically the slide is rocketed backwards by the hot gas to complete the cycling.

Okay, next rabbit hole is canting of sight and its effects on POI, if there is still interest from the forum.

Before going down the hole, let's take a sidetrack. Why is it dangerous to shoot a gun under water?

-TL

Sent from my SM-N960U using Tapatalk

[tangolima]

I'm compiling a dope chart for my .22LR rifle out to 300yd. I have the elevations from actual test firing. But I need windage dope, assuming 10mph full value cross wind. I can't use ballistic calculator as I don't know the bullet's BC. Well I could, by extracting the bullet's BC, but it is unnecessarily messy.

Here are relevant figures
Distance 200yd
MV 1250fps
Elevation 22MOA
Zero 50yd (It is a first crossing zero)
Sight height 1.5"

I managed to come up with a method that works quite ok. Give it a thought if it interests you. I will post details of my approach later. Hint: flight time is the key.

-TL

Sent from my SM-P610 using Tapatalk

[stagpanther]

I shoot a lot of 22lr out to 200 to 250 yds as well; very interested in your results but perhaps this would be a better topic on a different thread? So far my experience with any velocity 22lr ammo is that a crosswind of 10 mph for long distances shooting is going to scramble the impacts--no matter how fast the bullet is flying given existing 22lr bullet designs. I've shot lots of cartridges at those distances and have yet to come up with any "definitive" correlation between velocity and accuracy. But I keep hoping and trying nonetheless.

[JohnMoses]

A couple of points-
1) no one has mentioned secondary recoil. The energy to make all this happen comes from a phase change from solid to gas. This is a constant - powder type does not matter, the solid gunpowder increases its volume by a factor of 7000 ( I think). Thus you need to know powder charge and gun weight to calculate recoil.
2) Bill Davis, inventor of the 'bulletproof' vest, would stand on one leg on a 5 gallon bucket and shoot himself with a 44 mag and eventually a 308 H&K to prove you don't get knocked down. Newton was right.

[tangolima]

Finally a reply! Contemplating this sort of topics is part of the reason I enjoy this hobby. I have been trying to keep this thread alive so that we can have enjoyable conversations. The result so far is mixed at best. One more try perhaps.

I totally agree with your observation on .22LR. Its MV and BC are so low that any disturbance in the air will easily push the projectile off course. The windage dope is certainly a bit on the academic side. It assumes consistent wind at all points along the projectile's journey down range, which is of course impossible. However, I have found it quite useful as a starting point from which small adjustments are made on shot-to-shot basis, based on the shooter's ability to detect variations in the wind. On range, before firing, I usually would spend a few minutes to read the several things that tell the wind; flags, grass, etc, paying more attention to locations near me than the target. I try to come up with a figure of "prevailing cross wind". With that I look up the dope and dial it in. Then I fire a few shots on the berm to verify. Adjustments thereafter are mostly made by hold-over with reticle.

All the literatures on external ballistics I have read so far point to one common factor; the projectile's flight time. Less flight time, less error. For that I came up with a figure of merit to gauge performance of a bullet. It is the product MV*BC. Higher the better.

I will write up the details of my method and post it in a few days. Hopefully it will gives interested folks a chance to think about it. I'm delighted to share what I have found, but will be more so if someone can beat me to it.

-TL

Sent from my SM-P610 using Tapatalk

[tangolima]

Got home from a trip. Fighting off jet lag and a bug picked up in flight, I finally can get back to this one.

The dope in my previous post was pulled out of my memory. There are a few errors. Let me restate.

Distance 200yd

MV 1250fps

Elevation 26MOA

Zero 50yd (It is a first crossing zero)

Sight height 1.5"

Here are the steps.

The gun's bore inclines above the horizontal line by an launch angle A.

For 50yd zero, A=1.5/50*100=3MOA

For 200yd zero, A = 3 + 26 = 29MOA

A << 6 degree, so principles of flat firing apply. Flight time can be estimated from bullet drop d.

d=29 * 2 = 58" or 4.8'

Actual flight time

tf = sqrt(4.8 * 2 / 32.34) = 547ms

Flight time in vacuum

to = 200*3/1250 = 480ms

10mph wind is equivalent to 14.7fps.

Following point mass model, the wind deflection at 200yd is

w= (0.547 - 0.48)*14.7 = 0.98' or 11.8" or 5.9MOA

A few points to note
1. This method applies to all similar situations, where actual vertical dopes are known. Handy for cast bullets with unknown BC.
2. Flight time is estimated by gravity only. Actually flight time is always longer, although slightly for short distances.
3. Wind deflection (windage dope) is proportional to the cross wind speed. 5.9MOA @10mph, 3MOA @5mph etc.
4. Putting the equation in spreadsheet can be a useful tool.

Hope you find this interesting.

-TL

PS I'm putting together a spreadsheet of this. PM me if you want a copy.

Sent from my SM-P610 using Tapatalk

[tangolima]

Originally Posted by JohnMoses

A couple of points-

1) no one has mentioned secondary recoil. The energy to make all this happen comes from a phase change from solid to gas. This is a constant - powder type does not matter, the solid gunpowder increases its volume by a factor of 7000 ( I think). Thus you need to know powder charge and gun weight to calculate recoil.

2) Bill Davis, inventor of the 'bulletproof' vest, would stand on one leg on a 5 gallon bucket and shoot himself with a 44 mag and eventually a 308 H&K to prove you don't get knocked down. Newton was right.

JohnMoses. The discussion has changed topics several times. Please read the early posts. Newton wasn't wrong, but the way we apply his principles may be. Thanks.

-TL

Sent from my SM-P610 using Tapatalk

[Unclenick]

That method of calculating wind deflection was first published by a French artillery officer named Didion in, IIRC, 1868. He authored a book on the basics of ballistics for military academy students of his time, and it was included in it.

For those unfamiliar with the principles, even though commonly called "wind drift," bullets aren't actually drifting in the wind due to it blowing sideways on them. Indeed, they are so fast that any air molecule that glances off the side of the bullet will do so at an extremely acute angle, meaning there is no direct sideways blowing of air on the bullet. For that to happen, the air mass would have to be both moving forward at the speed of the bullet plus be moving sideways. Instead, what happens is the side wind and the headwind from the speed of the bullet combine into a vector that is a little off straight ahead in the windward direction. Precession tilts the bullet nose into this slightly angled headwind so that drag is no longer straight back toward the gun but rather is angled like the headwind. It is the sideways component of that drag vector, due to that angle, that moves the bullet sideways. So, if the headwind is at 1250 fps, and the sidewind is at 14.7 fps, 1250/14.7 is about 85, and thus a side-directed force equal to about 1/85 of the drag force on the bullet will be moving the bullet to the side.

Knowing that much, you next want to know how much drag is on the bullet. The difference in actual TOF in the air from what it would be in a vacuum tells you how much drag force has decelerated the bullet on its way to the target. If you know the mass of the bullet, the calculation of the average decelerating force is trivial (F=ma). You would then calculate how far 1/85th of that force would move the bullet during its TOF to learn the wind deflection.

Fortunately, there's the shortcut observed by Didion, which is simply to multiply the wind speed by that vacuum-to-actual difference in TOF. It is all really doing the same thing, but it gives your brain a fun puzzle to see why that has to be so.

This bit of reality bedeviled F. W. Mann in his 1907 book, The Bullet's Flight, from Powder to Target. He apparently never saw Didion's work. The poor fellow never did understand how wind drift works, and was clearly much vexed by fact that if he dropped a bullet in a crosswind from a height that gave it the same time of fall as its fired TOF was to a target, it was blown only a fraction of an inch instead of the the several inches the bullet was deflected by wind at that target.

A number of years ago I wrote a point mass solver in Excel because I wanted to be able to see intermediate calculation results that aren't displayed in a commercial ballistics programs. One of the interesting things I hadn't considered when I started the project was that the height of the apogee above the gun muzzle when firing at a positive angle of departure, plus the fall from the apogee to the target, would not add up to the total drop. Total drop is how far a bullet falls below a bore-sighted target when the bullet is fired truly horizontally. This is because, when you fire angled up, drag on the bullet can be divided into horizontal and vertical drag vectors. At the start, the vertical component of drag is pointed downward, so it assists gravity in slowing the bullet's climb. But when the bullet passes apogee, it starts turning downward, so the vertical drag component is now pointed up and fighting the pull of gravity. You might think the two halves of the trajectory, adding to and subtracting from gravity, would simply cancel each other out, but the fact the bullet is slowing and having its total drag decrease as it flies, and that this decrease is non-linear, plus the fact the arc of the trajectory bends down faster and faster as the bullet goes downrange, increasing the vertical portion of the total drag, all adds up to long range drop becoming significantly smaller than the gravitational constant and time of flight predict. You really need to shoot in a vacuum to make that work out.

[44 AMP]

Physics is a wonderful way to describe what we observe happening. But, sometimes, its doesn't seem to make much sense, though the math always "computes" the reasoning sometimes escapes me.

Perhaps they use the term "relative" for that reason??

One of the homework problems a co worker who was taking those classed had always baffled me.

Swimmer in a pool, swims to the far end, then back, gets out the same exact spot he went in. That was the set up, the problem the student had to solve was, using the formulae provided, they were to prove the swimmer went no where.

The math did work out. Only the logic didn't, for me. In "hobbit terms, he went "there and back again", but in math terms, since he started and ended in exactly the same spot, he "went nowhere".

Sometimes this "math vs, objective reality" gets applied in firearms discussions. Sometimes its on point, sometimes, its not. Sadly, I missed this thread when it was active last fall, or I would have responded to a number of points brought up then, but I won't now, unless they come up again.

Suffice to say that that not everyone's understanding is the same.

[tangolima]

Robert McCoy derived the same equation in his book. It is based on point mass model, if I remember correctly. The cross wind produces a sideways force following the same drag force model. Such force accelerates the bullet sideways.

The theory is neat and simple, at least the end result is. In real application, getting TOF is pretty hard. I try to estimate that from the elevation dope at different distance. There is still holes in the method. The hard and questionable part is estimating launch angle for zeroing. Sight height and first crossing zero is suspicious, especially for slow projectiles such as .22LR. I have an idea but I will need to do some tests first.

-TL

Sent from my SM-N960U using Tapatalk

[Unclenick]

I added a paragraph to my post while you were both posting. It explains a little more of what is going on.

Where sight height is concerned, the gun's bore line has to be at the same angle above horizontal to hit the middle of the target regardless of sight height. The sight setting, however, has to be adjusted to compensate for what that sight height adds to the angle of view but not to the angle of departure.

I've tried before to give folks a non-physics, non-calculation-based demonstration of how wind deflection works, but it hasn't always connected. I take a sheet of paper and tell them it represents the mass of air between the shooter and the target. Then I have them hold a Flair pen against the paper near one edge, telling them the tip represents the bullet. Next, I push the paper sheet straight toward them and ask them to focus on feeling what direction the drag is in. This is analogous to a bullet traveling in a straight line across the air mass between the gun and the target in zero-wind conditions. The drag direction, of course, is opposite the direction the line is being drawn in, straight back toward the gun. Next, I repeat, but this time I push the paper both back and sideways to simulate the air mass having a crosswind. This time, the line is diagonal rather than straight across the page, and of course, the drag is again felt in the direction opposite to that in which the line is being drawn. This means the drag is felt at the diagonal angle and not straight back toward the "gun," and that sideways portion of the drag is why, when you've set the sight to compensate for a crosswind, if you could see the bullet heading downrange in your scope, it would appear to first go to the windward side and then hook back to land in the bull's-eye.

[tangolima]

In a dope table, elevation is 0 at zeroing distance (50 yd) is this case. At other distances, additional angle (elevation dope) is added to the zero elevation. In other words, elevation dope is angle relative to the zero.

But we need to know the angle between the bore axis and horizontal line (launch angle / angle of departure) in order to calculate the bullet drop. We won't know that until we figure out the absolute launch angle at zeroing. Here I am taking a short cut. 50 yd is a 1st crossing zero. Assuming the gun is horizontal (fallacy #1) and negligible gravity influence on the bullet (fallacy #2), such launch angle can be estimated with the sight height. Errors happen, especially for slow moving bullet, due to the above 2 questionable assumptions. That's what I'm going to tinker next.

Here bullet drop has nothing to do with line of sight. Imagine the bore of the rifle is set horizontal and fires. The bullet drop is relative to the horizon bore axis. By principle of flat firing (launch angle much smaller than 6 degree), such drop can be estimated with the launch angle. Here lies fallacy #3, the bullet's vertical fall slows down as the speed picks up. For now I'm not going to worry about that.

It may be a bit beyond the scope of current discussion, gyroscopic stabilization of a aerodynamically unstable bullet has brought me a few more grey hairs. Bottom line is the bullet will end up with a posture (yaw and pitch) that lessens the external perturbation. A left cross wind makes bullet point to left and down, and a right cross wind makes the bullet point right and up. It lessens the effect of the cross wind by pointing into the wind. But the bullet itself keeps moving down wind. It may appear in the scope that the bullet gains on the wind. It is because of the correction angle (windage) we put in. We shoot more into the wind waiting for the wind to push right back on.

-TL

Sent from my SM-N960U using Tapatalk

[stagpanther]

And now for something completely different.

Wind does not push a projectile moving faster than the velocity of the wind--the airmass carries it. I've always had a contrarian point of view of these things as a result of many years of being a glider pilot. Wind is not a bunch of arrows flying around that when it collides with an object pushes it--it is the movement of air masses generally resulting from barometric pressure gradient differences. Individual molecules of air may have little mass--but large bodies of air can have tremendous mass. Air masses moving along the surface almost never move in a linear flat constant angle because of advective disruption with the objects on the surface (trees, rocks, buildings, mountains etc.). Even out in a perfectly flat desert--or ocean--the wind can be disrupted by convective heating--rising columns of air. it doesn't take much to trigger a release of a column of heated air from the surface--and it will continue to rise as long as there is a temperature difference between the heated mass and the surrounding air's temperature (lapse rate) of approximately 3 degrees.

The best way for me to try to "understand" air movement is to think of it in terms of fluid dynamics--much like water in a stream that flows up, over and around rocks but also is upset and creates eddies, downflows and rotations. Temperature also plays a big role in both heating and cooling of the earth's surface. 22lr shooting is great in a sense because it readily shows the effect on the trajectory of the bullet more obviously than other cartridges with slight changes in the environmental conditions (especially as the range goes out beyond 50 yds).

Fire away!

[tangolima]

Push, carry, pull, lure, whatever you term it, the cross wind exerts a lateral force on the projectile to make it move sideways. That's the bottom line. My take on this may be different from unclenick. The cross wind and the bullet's velocity are orthogonal vectors. They are independent from each other. The high bullet velocity has no bearing on the effects of the cross wind. It is everywhere along the trajectory, so it doesn't have to run as fast as the bullet and keeps blowing on the bullet. So the generic approach is to have 2 drag models, longitudinal and lateral. But this is unnecessarily over complicated. In exterior ballistics, we are dealing with a special case where bullet velocity is orders of magnitude higher than the cross wind.

Derivation of the said equation show that such special case can be sufficiently described with only the longitudinal drag model with slight change of angle of attack.

-TL

Sent from my SM-N960U using Tapatalk

[stagpanther]

The high bullet velocity has no bearing on the effects of the cross wind. It is everywhere along the trajectory,

Partially true IMO--the bullet velocity does not somehow affect the wind--but the amount of time the bullet is in the airmass that is moving most certainly affects the wind drift of the bullet.

[tangolima]

Originally Posted by stagpanther

Partially true IMO--the bullet velocity does not somehow affect the wind--but the amount of time the bullet is in the airmass that is moving most certainly affects the wind drift of the bullet.

In terms of TOF, I agree.

-TL

Sent from my SM-N960U using Tapatalk

[Unclenick]

Blowing on Bullets:
If only the wind pushing on a projectile explained its deflection to the side, same-weight, same area, higher BC bullets would have no less wind deflection for a given time of flight (TOF) than blunt shapes do, but they do have less deflection. When it comes to which otherwise-identical bullet will be least deflected by wind during a given TOF, it is always the one with the highest ballistic coefficient. That is because it has lower drag turned into the wind vector. It is the wind vector, in effect, steering the direction of drag that causes wind deflection. There is not enough direct force from a side wind to produce the amount of wind deflection that actually occurs.

An Example:
A CCI 22 LR Standard Velocity round is fired from a rifle at the factory-claimed 1070 fps. Its flat fire TOF to 100 yards in an ICAO standard atmosphere is 0.3024 seconds. If it is fired in a 10-mph crosswind, it will deflect 3.877 inches at the target. If we calculate how far the wind could blow that bullet in that circumstance, we get a much smaller number. About 0.068 inches. Even if we pretend the bullet doesn’t yaw to point into the wind and instead pretend the wind moves with the bullet and blows on the side of it, in 0.3024 seconds, it works out that a 10 mph wind will blow the bullet, not quite 0.55 inches. So there is no way to account for the observed amount of deflection by having the wind blow on the bullet.

I have attached a file with the calculations for anyone interested in them.

Estimating TOF from Bullet Drop:
In the air, everything has a terminal velocity. Assuming point-forward bullets, those with higher ballistic coefficients will have higher terminal velocities. This means that when fired at the same velocity as otherwise-identical bullets with lower BCs, their total drop will be greater. If I fire the old Hornady .308" 150-grain RN at 2800 fps, after 1 second, it has traveled 525 yards and has a total drop of 141.5 inches. If I fire the Hornady .308" 150-grain FMJ BT at the same velocity, after 1 second, it has traveled 674 yards and has a total drop is 157.4 inches. A bullet dropped in a vacuum, using the 32.17405 ft/s² gravitational constants, will fall 193.04 inches in 1 second so that you can see almost a quarter of the gravity drop is being shaved off by drag.

Estimating TOF from bullet drop is most easily done using a point mass solver. If you know your muzzle velocity and zero, plug those in, then tweak the BC until you see the same drop on paper that you actually measured. At that point, the program’s TOF should be a good match.

[tangolima]

Thanks Unclenick. I will have some time this week to go through your calculations and the one I picked up from the book(s). The cross wind causes the projectile's wind deflection by the amount given by the equation (TOF - To) * Vw. The exact mechanism, should it be push, pull, drag, or whatnot, we will explore further. This is my take. The key, and in fact to almost all exterior ballistic parameters, is TOF. Shorter TOF, the better.

In the meantime, I'd like to open up a new rabbit hole. This one is also related to exterior ballistics, and it has more flavor in maths than in physics.

When browsing youtube, I came across this idea of "weaponized maths". https://www.snipershide.com/precisio...aponized-math/.
It is basically a method to estimate elevation dope in lieu of a ballistic calculator. After zeroing the rifle, say at 100yd. The shooter shoots again at another distance, say 300yd. From the bullet drop, he can quickly estimate the dope at other distances up to, say, 1000yd. This is done without knowing the MV and BC, and without a ballistic calculator at hand. Just use the calculation form provided. I think it is pretty cool.

I went ahead and did my own equation manipulations and number crunching. I came up with an improved version of this method. I still need to fire at one distance after zeroing. Instead of using the calculation form, I just need to remember one constant, which is specific to the type of the bullet. It is pretty cool too!

I will share the details in a later post. In the meantime, if you are interested, please read and understand the original method following the link. It is a bit convoluted, but quite simple really.

Have fun!

-TL

Sent from my SM-P610 using Tapatalk

[stagpanther]

In addition to the formulas you use in your calculations--it would be useful to see how they match up to actual in-the-field shooting. The interesting thing about 22lr is that it "compresses down" observable effects in relative short ranges that make them easily observable in terms of drop/drift. While the physics of bullets are generally similar--I think 22lr is somewhat unique in the method of compressing the lead projectile into the chamber and down the bore which makes it "apples to oranges" to some degree when comparing it to faster jacketed centerfire cartridges. I often see dispersion in cross winds in which the vertical seperation is equal to or greater than horizontal when shooting 22lr. If I can get the wind as close to my 6 as possible the effects are minimized to a greater degree than trying to compensate for head or crosswinds.

[tangolima]

To be honest, I haven't rigorously tested the calculations in the field yet. I don't have a anemometer. Have been looking for one on and off.

Rather I just eyeball the wind indicators, flags, grass, etc, on range to come up with a estimate on cross wind. I refer to the weather report of the day too. Then I plug it in the equation to come up with windage dope. Pick a point on the berm and fire a couple of rounds. Measure the windage of the poi with the scope reticle. There are always errors. 2 or 3 moa is common. Then I dial it in and start "firing for effect", adding in small hold over for each round as it goes.

-TL

Sent from my SM-N960U using Tapatalk

[stagpanther]

Found an interesting article that takes a good look at factors that influence drop/drift of 22lr. I like the emphasis on transonic zone and where/when it happens, and to what degree. The author also looks at scaling the ballistics of 22lr to that of bigger centerfire cartridges as an obvious boon to training. I'm not exactly sure that scaling can be done reliably in a linear way, I find very small variations in environmental conditions can have profound consequences on the bullet's drag/stability anywhere along its trajectory. Good food for thought.

[tangolima]

Great. More materials for lunch time reading.

I like to use TOF as reference for comparison. It is about 0.5s for HV .22LR at 200yd. It is equivalent to 400 to 500yd for center fired calibers. At 500yd, a center fired rifle is doing quite well if it hits a 8" target consistently. It matches my .22LR rifle at 200yd. I can hardly hit soda can one out of 10 shots. But I'm confident of hitting 8" plate one out of two.

Scaling factor is about 2.5x, the way I see it.

-TL

Sent from my SM-P610 using Tapatalk