I dont understand the whole "gun will hold _moa @ _yrds".

[slate84]

If you can go out and shoot say a 1/2 group at 100y, why would that not mean that your rifle wouldnt hold that same moa throughout the upper yardage? Isnt it all external balistics at that point and falls more on the ammunition than the rifle? I always read people saying their rifle will hold say 2moa out to 600y but is that more of a statement towards the conditions and ammo then the rifle? I just don't see how a rifle that could print 1/2 groups at 100y could become less accurate in an ideal setting and that all other rifles would be just as susceptible to said outside forces.

 

[tmxring]

I think it has something to do with the bullet stabalizing. If a bullet leaves a not very smooth/true bore maybe the bullet doesn't have time by 100yds to start showing signs of in-accuracy. It probaly has enough speed at short distance to not notice it. I don't have a magical answer to your question. But I've seen and owned many factory rifles that would shoot under 1/2"@100yds but would shoot 2-3"@200yds. IMO that's where a custom barreled rifle is worth the money. Typically a custom rifle that will shoot 1/4"@100yds will shoot 1/2"@200 if the shooter does their part.

 

[Dirty D]

Holding all variables constant at say 600 yards that are encountered at 100 yards you are correct, the problem is there are more variables that come into play at distance. Cd (coeffecient of drag) slows the bullet in flight and the slower the velocity the more the bullet is affected by air movement. There are lots more variables and people here that are much more qualified than I to explain them. Another variable is flat base bullets vs boattail bullets, flat based bullets can be extremely accurate at 100 yards but at longer ranges as they slow the flat base causes more turbulence behind the round. Boat tail bullets experience less turbulence by virtue of the bullet shape, a phenomenon known as laminar flow plagued Chuck Yeager and the X-1 program until they developed the flying tail, laminar flow is a bullets friend for the same reasons that it interferred with an aircrafts ability to manuever.

My entirely unqualified .02

 

[buffybuster]

If you can go out and shoot say a 1/2 group at 100y, why would that not mean that your rifle wouldnt hold that same moa throughout the upper yardage? Isnt it all external balistics at that point and falls more on the ammunition than the rifle? I always read people saying their rifle will hold say 2moa out to 600y but is that more of a statement towards the conditions and ammo then the rifle? I just don't see how a rifle that could print 1/2 groups at 100y could become less accurate in an ideal setting and that all other rifles would be just as susceptible to said outside forces.

If this were to the case, then shooters would regularly shoot clean F-Class scores......

The reasons a rifle will not hold accuracy at distance is complex but can be broken down into:

1. Ammunition: If there is excessive Extreme Spread in velocity that will result in greater vertical dispersion. If there is BC variance in the bullet, that will result in greater vertical and horizontal dispersion. This issue may not be noticeable at close range but will reveal themselves at long distances.

2. Bullet precession: If the bullet is not perfectly internally concentric, it may not spin on its exact centerline. That will result in bullet wobble at longer range.

3. Over or Under Spin of Bullet: Over spin could make the bullet weather vane slightly, altering its effective BC at long range. Under spin would make the bullet unstable and begin to wobble.

4. Barrel harmonics: If the bullet does not exit at the exact same harmonic point, there will be greater dispersion. OCW load development is to address this.

5. Those pesky environmental conditions. Wind, Mirage, Wind, Wind, Temperature, Curavture of the Earth, Coriolis Effect, The Amazon Rainforest, the Polar Ice Cap, Cows Farting, etc..

6. Loose nut behind the trigger.

Those are the high points. There are MANY other minute details.

 

[slate84]

So its basically an ammo rifle combination and not so much that the rifle only shoots truly accurate at certain ranges.

 

[M40_A1]

So its basically an ammo rifle combination and not so much that the rifle only shoots truly accurate at certain ranges.

It's mostly ammunition/environmental variations, but barrel twist is also a possible factor, as mentioned. Otherwise, the barrel doesn't know what range the bullet will impact, so harmonics at long range will be the same as at shorter range.

 

[bodywerks]

As the distance increases, effects of mirage, wind, muzzle velocity variances, spin drift, gyroscopic effects, all become amplified. It's really as simple as that.
Even assuming it's a cloudy day and no wind whatsoever, a simple muzzle velocity inconsistency of, say, a 30fps spread would open up a 700yd group tremendously.

Sent from my SCH-I545 using Tapatalk

 

[KYpatriot]

The are two main reasons dispersion is not linear with distance. First is that it is dependent on time of flight, not distance. The external factors that cause dispersion in a group act upon the bullet over time, and obviously the more time they have to act the more dispersion they cause. If you have a weapon that shoots 1/2in groups at 100 yards, it is tempting to think that at 1000 yards it will simply shoot ten times the 100yard group. It will not, because the TOF at 1000 yards is always more than ten times the TOF at 100 yards because the bullet loses velocity rapidly.

The second reason is that it is far easier to make aiming errors at 1000 yards than at 100yards. Quartering a bull is easy at 100 yards, but much less definite at 1000.

For example: Estimating the correction for wind is much easier over 100 yards than 1000, and remember that any wind error will be dependent on TOF so again that makes any such errors worse at 1000. At 100 yards a 308 with 175SMK, density altitude 2500', launched at 2715fps takes 0.114sec to reach 100yards. That increases to 1.645secs at 1000 yards. 1.645/0.114 equals 14.43, so we can expect a little over 14 times more dispersion at 1000 yards instead of 10 times the 100 yard value. And THAT 14 times assumes a perfect wind solution, which is far more difficult at 1000, and doesn't even account for any additional aiming error caused by the difficulty in seeing the target/relative target size.

If you really care about the subject get Bryan Litz's book:

AB for Long Range Shooting

PS. Pre-emptive strike: While tmxring hinted at it, glad to see the "go to sleep" crowd skipped this one. While it is true that epicyclic swerve (the bullet steering itself along a corkscrew flight path due to its nose coning around) can cause some dispersion that dampens out if a bullet is dynamically stable (commonly called "going to sleep"), we are talking about dispersions less than a tenth of an inch. The effect is at least an order of magnitude too small to overcome dispersion relative to TOF. If the phenomenon of smaller groups at distance exist, the laws of physics demand something else is causing it...in other words all the other variables are not constant. Rather than muddy this thread with that, see the one here:
https://www.snipershide.com/shootin...-sleep-get-more-accurate-longer-ranges-2.html