Accuracy Question

Ghost Recon

Hi All!
A quick question in terms of absolute accuracy and for ballistic data purposes, etc. - when measuring a distance to a target, do you measure from:
- the muzzle?
- the objective lens?
- the chambered round?
I guess I’m just a bit of a perfectionist and like to get things 100% correct!
Thanks in advance for the replies!
Regards,
GR.

Ghost Recon

Hi All!
A quick question in terms of absolute accuracy and for ballistic data purposes, etc. - when measuring a distance to a target, do you measure from:
- the muzzle?
- the objective lens?
- the chambered round?
I guess I’m just a bit of a perfectionist and like to get things 100% correct!
Thanks in advance for the replies!
Regards,
GR.

alanmc

I'm no expert. But I'd imagine from the muzzle. As that's when the bullet will start to decelerate and drop.

As I said, I'm no expert, but that's what I'd imagine. In practical terms, will it make much of a difference though?

juice1304

You measure from the muzzle, the calculations are based on the speed of the round, the weight of the round and the ease at which it cuts through the air(in its more simple form without adding in all the other variables like Coriolis effect etc..). And in the grand scheme of things 1 meter is not going to make any difference.
Something important if you are a perfectionist is to have an accurate measurement of the hight of your scope in relation to the central bore axis. If you have a calipers measure the diameter of your barrel at the chamber divide it by two, divide the diameter of your scope tube by two and measure the height of your rail, rings etc..

dc99

I am deffo not an expert, but I would have thought that it is possible that the bullet could stil be accelerating after exiting the muzzle?

alanmc

dc99 wrote: »

I am deffo not an expert, but I would have thought that it is possible that the bullet could stil be accelerating after exiting the muzzle?

Maybe. But once it leaves the muzzle, it has drag and gravity acting on it and very little in the way of thrust from the gases. I'm probably wrong though. It wouldn't be the first time I'd be wring about the physics of shooting.

Ziggieire

Ballistic calculators take the vocality from the muzzle and extrapolate the curve from there.
but the extra lets say 1.5 meters behind the muzzle, i do not think anyone can achieve such a feat of consistency and accuracy to make a difference.
i think Applied Ballistics plots 5 meter intervals. and inside 5 meters out to 600m+ there might be less than 0.1 milrad drop.

dc99

alanmc wrote: »

Maybe. But once it leaves the muzzle, it has drag and gravity acting on it and very little in the way of thrust from the gases. I'm probably wrong though. It wouldn't be the first time I'd be wring about the physics of shooting.

Oh it will definitely start slowing down - that's a given, but when! that's the question. - so many variables - but I also will wait for the more knowledgeable post the info here :-) no offense intended to anyone :-) just an interesting question to listen for an answer.

tac foley

Once the projectile has left the muzzle - the point called 'shot ejection' - it ceases to be acted upon by the expanding gases that sent it on its way in the first place. The deceleration begins instantly.

The rate of deceleration is dependent on a number of criteria - including the ballistic coefficient of the bullet, the air density through which it is travelling and therefore the height above ground [the higher you go, the less dense the air is], the ambient temperature and so on. The forces that act on the bullet are also many - drag, induced by the shape of the bullet, especially around the base, hence the development of boat-tailed bullets to reduce the drag, and the actual shape of the frontal part of the bullet as it penetrates the air. Longer, so-called VLD [very low drag] bullets, are designed to retain their velocity over a longer range. This does not mean that they never lose velocity, only that they DO lose it, but slower than a blunt-nosed bullet. Imagine the difference between the stem of an oil-tanker and a racing yacht as they cut through the water.

Cass

Ghost Recon wrote: »

Hi All!
A quick question in terms of absolute accuracy and for ballistic data purposes, etc. - when measuring a distance to a target, do you measure from:

God answer by Juice1304 which covers all you need.

dc99 wrote: »

Oh it will definitely start slowing down - that's a given, but when! that's the question.

Educated guess, from the moment it leaves the barrel.

From the initial firing of the primer, the burning of the propellant and the pressure from this the bullet is pushed down the barrel. However as soon as the bullet exits the barrel there is no longer any force acting on it and it starts to slow immediately.

Zxthinger

Seriously It's make no difference.
The bullet is only ballistic upon exiting the bore. The Guinness book of records would I think measure from the muzzle,.,?!?,
However the calculations in most programming suites computes the drop relative to the 'scope above bore height' which starts at the chamber.

Wait till you're worrying about how to fix your recoil lug? Pinned or tig welding? Lol

Ghost Recon

Thank you everyone for the detailed replies - much appreciated!
I had assumed to measure from the muzzle, so will continue with same.

Feisar

Muzzle, but yer spliting hairs, or as the boss does like to say, "deck chairs on the Titanic."

tac foley

Muzzle energy and muzzle velocity are measured at the muzzle, that's the reason for calling them what they do. The fact that a chronograph us usually set up at a set distance between it and the muzzle is an allowable discrepancy, bearing in mind that the measured loss of velocity in ten feet is, to all intents and purposes, absolutely negligible. FWIT, the loss of velocity of a bullet travelling at 3500 fps from the muzzle is

Downrange ballistic data, such as that used by reloaders, give all the drop and loss of velocity figures out to the time that the projectile hits the ground. Remember that both velocity drop and muzzle energy loss are not linear - as the bullet loses velocity, so it loses energy, too, and all these things depend on the ballistic coefficient of the projectile - BC and all the other variables I mentioned before.

An example here is a 55gr .223 bullet, leaving the muzzle at 3239fps with 1281 ft lbs m/e.

49 milliseconds later, at 50 yards, it is travelling at 2992fps, with 1093 ft lbs of m/e.

I'll allow you to do the diffcalc that works out how much it will have lost at a distance of ten feet from the muzzle, but i can reliably inform you that it is significantly less than diddly squat.

To sum up, the fastest that a bullet will EVER be travelling is as it quits the muzzle - the gas that is driving it no longer acts upon it. So where does it all that gas go?

Every stood or lay down near a rifle with a muzzle brake fitted?

Now you know, right?

And BTW, what has this to do with accuracy?

And how do you figure on measuring all this stuff right there at the muzzle?

Ghost Recon

I think my original question has perhaps been lost among the various replies?!
All I wanted to know was that if I am zeroing at a measured 100 yards from point A (shooting position) to point B (target), where does point A begin?
I just wasn't sure if point A was to be the muzzle, the objective lens, or the chambered round!
From the replies received, it would appear to be the muzzle, which makes sense!

Benny mcc

How long is your barrel? How long is your scope? What difference will it make? Would anyone consider any of this in relation to distance for zeroing a rifle no

slipperyox

I'd imagine some bullets will begin slowing down before leaving the muzzle.
via friction (deep lands and grooves), too long a barrel, and fast burning powder?

tac foley

As the rate of slowth [is that a word?] between the muzzle and a chronograph set up at the usual ten feet away must be measured in literally tenths of thousands of feet per second, it is my belief that you are trying to needlessly overly complicate something that we all do every time we try out a new cartridge or set up a new gun without overly worrying about it.

Just as a matter of interest - to some - the 55gr .223 bullet of x BC has lost 16.4646 fps between leaving the barrel at 3239 fps, and passing over the chronograph set up ten feet away. The bullet took 0.000326-0003285 seconds to travel that distance, slowing down as it did so, of course, due to air density, gravity, humidity and so on.

Given that every bullet we ever fire, despite the wonders of modern manufacturing, is going to be slightly different from the next one, or the last one, I think that the actual physical distance between your eyeball, the bullet in its position at the front of the cartridge case inside the barrel, and the muzzle where it eventually peeks out into free air, you are wasting valuable shooting time by worrying about it.

The position of the front, the middle or the eye-piece of the scope matters not a jot, since it has no bearing whatsoever on the performance of the bullet.

juice1304

slipperyox wrote: »

I'd imagine some bullets will begin slowing down before leaving the muzzle.
via friction (deep lands and grooves), too long a barrel, and fast burning powder?

Yes, that is correct.

ejg

Easy, just look at how much difference in drop you have at 100m vs 101m, try the same at 200m vs 201m. If the difference is bigger or much bigger than your normal group size at that distance then you should think about where to measure from and your measuring technique. Rangefinders... +- 1m?
edi