Better Groups at Distance

[Axl]

Guns and Ammo just had an article about boat tail bullets not stabilizing until about the 300 yard mark, while flat base bullets stay stable right out of the barrel to 400 yards.

Well here is that article and nowhere in it does it say any of that

Rifle Bullet Designs - Guns and Ammo

A primer on rifle bullet designs.

www.gunsandammo.com

 

[Canadian Bushman]

Guns and Ammo just had an article about boat tail bullets not stabilizing until about the 300 yard mark, while flat base bullets stay stable right out of the barrel to 400 yards.

There is some truth to this, but i feel they have their facts a bit crossed up. There is usually some initial instability when a bullet leaves a barrel. Bullets are never perfectly balanced, nor will they always enter the rifling with their axis perfectly parallel to the bore axis. Also the high pressure gas driving the bullet is going to try to overcome the bullet the instant it has a path to do so. All these variables contribute to the bullets initial yaw when it exits the barrel. Boat tails certainly help the muzzle gases overcome the bullet and affect its initial instability problems.

However I believe a properly stabilized bullet settles down much much more rapidly then 300 yards. In fact many benchrest shooters have shot their heavy guns through rows of card stock at a few feet from the barrel to confirm bullet stability of a bullet barrel combo before pouring tedious effort tuning because they felt quickly stabilizing bullets were key to long range accuracy.

Harold Vaughn has probably studied this effect in small arms the most thoroughly in his book "Rifle accuracy facts" and Bryan Litz, of course confirmed his findings in his books.

However the physics of this scenario have long been studied in field artillery and naval guns where long trajectories and high launch angles are much more dramatically effected by these conditions.

 

[ericbc7]

This apparent effect has never been documented in testing situations. I cannot see any cause beyond a shooter's technique combined with optics. If you set up your scope and rifle to print to the side of the aiming point on a 100 yd target and choose your aiming point at 300 yds (rifle still printing at 100 yd) you will always see proportionally smaller groups at 100 yards than at 300. In other words, if your rifle prints a perfect 1 moa at 100 yds, it will repeatably print larger than 1 moa at 300 due to more variables acting disparately and for more time on each shot. On the rare occasion that you get a smaller than 1 moa at 300, it is simply statistics attributable to the random nature of group size - it will not be reliably repeatable. I am not saying you won't observe the occasional smaller moa group at 300 vs 100 but if you observe it regularly, there is a problem with the shooter and/or the optics.

 

[73driver]

This apparent effect has never been documented in testing situations. I cannot see any cause beyond a shooter's technique combined with optics. If you set up your scope and rifle to print to the side of the aiming point on a 100 yd target and choose your aiming point at 300 yds (rifle still printing at 100 yd) you will always see proportionally smaller groups at 100 yards than at 300. In other words, if your rifle prints a perfect 1 moa at 100 yds, it will repeatably print larger than 1 moa at 300 due to more variables acting disparately and for more time on each shot. On the rare occasion that you get a smaller than 1 moa at 300, it is simply statistics attributable to the random nature of group size - it will not be reliably repeatable. I am not saying you won't observe the occasional smaller moa group at 300 vs 100 but if you observe it regularly, there is a problem with the shooter and/or the optics.

I statistically always tend to have better groups at 300 & 200 yards than I get at 100 yards, nothing rare about it, it just happens and I like it.

 

[Tangent]

I statistically always tend to have better groups at 300 & 200 yards than I get at 100 yards, nothing rare about it, it just happens and I like it.

No one is debating whether or not this happens to some shooters on occasion (or maybe even regularly for some). But the reality is that there is nothing magical happening to the bullet between 100 yards and 300 yards. It is merely errors from the shooter at close distances.

If you think otherwise, put paper up at 100 yards without a backer in the flight path of the bullet and shoot your group at 300 yards. Then prove that your 100 yard group is somehow bigger (in terms of angular subtension) than your 300 yard group.

 

[Canadian Bushman]

This apparent effect has never been documented in testing situations. I cannot see any cause beyond a shooter's technique combined with optics. If you set up your scope and rifle to print to the side of the aiming point on a 100 yd target and choose your aiming point at 300 yds (rifle still printing at 100 yd) you will always see proportionally smaller groups at 100 yards than at 300. In other words, if your rifle prints a perfect 1 moa at 100 yds, it will repeatably print larger than 1 moa at 300 due to more variables acting disparately and for more time on each shot. On the rare occasion that you get a smaller than 1 moa at 300, it is simply statistics attributable to the random nature of group size - it will not be reliably repeatable. I am not saying you won't observe the occasional smaller moa group at 300 vs 100 but if you observe it regularly, there is a problem with the shooter and/or the optics.

It has been tested and documented quite thouroughly by Bryan Litz. Chapter 2 of "Modern Advancements in Long Range Shooting." He calls it "Angular group convergence."

 

[ericbc7]

It was tested by Brian Litz and shown not to happen. He even invited anyone to come to the testing facility to demonstrate a rifle and load that produced this effect to a significant degree and no one has done so.
im not trying to convert anyone who is very invested in this, but I am curious how 2 people can read the same book and come away with opposite conclusions on the same subject.

 

[Canadian Bushman]

It was tested by Brian Litz and shown not to happen. He even invited anyone to come to the testing facility to demonstrate a rifle and load that produced this effect to a significant degree and no one has done so.
im not trying to convert anyone who is very invested in this, but I am curious how 2 people can read the same book and come away with opposite conclusions on the same subject.

There was a Sako with a slow twist that occasionally showed convergence. Litz believed this to come from the lack of stability with a particular bullet.

He also proved that it was possible with barrels tuned for positive compensation. Where the launch angle differed with varying muzzle velocities that would offset each other at a particular distance. Which is still a very common practice in long range BR for keeping consistent aggs.

Litz struggled to prove this one as his shoot through range was only 300 yards and a much longer range is needed to fully explore positive compensation. However his computer simulations supported it.

 

[ericbc7]

I appreciate the response, i will review the testing when I get the book back.

 

[coop2564]

I do same, not sure of the reason but group better a longer ranges, unless it real windy.

 

[Canadian Bushman]

After i got an optic that was easy to set parallax free at close range, my 100 yard groups shrank right down to what they were doing at distance.

Parallax errors at close range are way more common than most people think. Especially with particular brands of optics.