[Roudy]

From time to time I hear or read about a firearm that " May shoot one MOA at 100 yards but will not necessarily shoot one MOA at 300 yards (or beyond)".

Now I have a very good understanding of the effects of wind, up drafts, down drafts, etc on the path of the bullet; but it seems to me that once a bullet leaves the barrel (barring effects of the air movement) it will travel in the same horizontal plane and be effected by the same amount of gravity as the next bullet, and the next, etc. (I assume accuratley loaded ammunition and a 'perfect' shooter)

Are the people that make these statements just perpetuating a myth or is there some scientific basis for their statements?

[30Cal]

If we were simply talking about aiming or pointing error, then yeah, a 1MoA rifle would shoot 1 MoA all the way out. But that's not the issue. The issue is a variation in velocity, harmonics, or something about the bullet's weight, ballance or aerodynamics.

Nothing about a bullet's flight is linear. The bullet drops faster the farther it goes. It's decellerating at a varying rate. Wind and environmental effects are compounded by range. These effects all grow with range. It doesn't make sense that accuracy would remain constant with range when everything else is not.

[rockstar.esq]

From time to time I hear or read about a firearm that " May shoot one MOA at 100 yards but will not necessarily shoot one MOA at 300 yards (or beyond)".


Are the people that make these statements just perpetuating a myth or is there some scientific basis for their statements?

The MOA thing is for a particular rifle. Now I have heard of situations with the .50BMG where the bullet isn't fully stabalized untill it gets a certain distance downrange. Another possible source for this phenomenon is when a bullet's speed slows from supersonic to subsonic. The sonic boom following the bullet sometimes disturbs the bullets track creating sub par accuracy. If the bullet starts supersonic and hits it's target supersonic, then the MOA should remain the same.

[USSR]

From time to time I hear or read about a firearm that " May shoot one MOA at 100 yards but will not necessarily shoot one MOA at 300 yards (or beyond)".

Now I have a very good understanding of the effects of wind, up drafts, down drafts, etc on the path of the bullet; but it seems to me that once a bullet leaves the barrel (barring effects of the air movement) it will travel in the same horizontal plane and be effected by the same amount of gravity as the next bullet, and the next, etc. (I assume accuratley loaded ammunition and a 'perfect' shooter)

Are the people that make these statements just perpetuating a myth or is there some scientific basis for their statements?

Roudy,

Sadly, the statement is true. How can this be? Weather conditions are always a factor since we are not shooting in a vacuum; there are no perfect bullets; try as we may, absolute consistency cannot be maintained in reloaded ammo; and lastly, there are no perfect shooters. I regularly shoot at 1,000 yards, and I will tell you that your 1MOA group at 100 yards don't mean squat when it comes to shooting long range.

Don

[bogie]

At 100 yards, you don't see a lot of vertical dispersion related to rifle characteristics (vibration, rough spots in barrel, etc...) or load characteristics...

At 200 yards, they become a lot more apparent. At 300 yards, they get downright ugly.

One morning at the NBRSA Nationals this year, I shot a .2005" aggregate at 100 yards. I couldn't get the rifle to stay inside a half inch at 200. Switched to a rifle that I didn't really like at 100, but it was more consistent at 200.

[Roudy]

Gentlemen....I appreciate all the discussion. Seems like there are people other than me with not enough to occupy their time (ha).

After digesting the information you have provided, the two things that makes sense to me is the idea of traversing the sonic barrier and the distance required to stabalize the rotation of a particular bullet.

When I have noticed these comments they are usually made in reference to a particular firearm. Barring atmospheric influences a particular firearm will produce a 'cone of fire' of a particular size at 100 yards. If that cone of fire is measured as an angle is one minute, then 'barring atmoshperic influences, that one minute of angle should remain one minute until the bullet impacts its target.

In reality the shooter, load variation, less accurate sighting at longer distances, and weather all have an effect on the accuracy of a firearm. It still puzzles me. I certainly appreciate you input!

[Medusa]

Quote my old post on similar matter:
Well, the coefficient of friction is proportional to the speed, at high speed it's proportional to the velocity's square, at lower speed to the velocity itself. So the trajectory of flight has a shape of ballistic curve instead of perfect arc, besides, other factors that affect the projectile's flight are gyroscopic effect, then the lift created by the spin (total blackout on the effect's name :cuss: ), drag that depends on bullet's shape (whether the airflow is laminar or turbulent at the boattail), then of course the Coriolis effect, differences in air density (by pressure and temperature) over the flightpath, fluctuating gradient vectors of pressure and temperature. Hmm did I miss something? surely did :banghead: Did I mentioned wobbling hands and breathing at the wrong time?

[Dave P]

Here is a site for you:

http://www.nennstiel-ruprecht.de/bullfly/

[Art Eatman]

"Now I have heard of situations with the .50BMG where the bullet isn't fully stabalized untill it gets a certain distance downrange."

Give that man $64 and a box of Mars Bars! :)

It's a mix of the twist of the barrel, the velocity of the bullet, and a few other factors. Some bullets become less stable with distance; others will "settle down" and actually group better at longer ranges.

That link given by Dave P is a good read.

Art

[Roudy]

Wow Dave P, this article sure explains a lot to me. I've always wondered how a given rifle and given load could shoot 3 MOA at 100 yds yet shoot one MOA at 500 yds. That explaination of the bullet yaw certainly could cause that effect.

Until now I've theorized that bullets have little beady eyes and devious little minds and would decide to become "accurate" after being "inaccurate". So much for that theory.

The website "How do bullets fly" ought to be on every serious shooters reading list. So much to learn yet, so much! (and I've only been doing this for about 40 years)

[miko]

I'd day, if a bullet is under-stabilized or over-stabilized - which depends on the barrel length and twist rate among other things but also air density, etc. - the problem may not be expressed at 100 yards but become quite pronounced over 100 yards - when the bullet starts tumbling or travelling sidewise.

miko