Hello to you all,

I just noticed something very strange at the range the other day. I was shooting some Barnes 270gr TSX at 100yrds when I noticed that I was grouping 3 inches left of center. I thought it was my scope going bonkers, but I decided to fire some 260gr Accubonds to check it. The Accubonds grouped dead center, so did the 270gr Hornady SP. I shot some TSX again, and same thing, they all grouped 3 inches left of center... Anyone else have this happen to them???

Thanks,

Mo

Enigma
Yes, I´ve had this problem and it was explained to me as follows :
As the bullet engraves the rifeling and speeds down the barrel, the end of the barrel describes a circle unseen to the naked eye, Different bullet weights at different velocities can be expected to leave the barrel at differing points on this circle thus, causing them to land left or right of centre. A fluted or hexagonal barrel is supposed to reduce this effect, giving a similar result to what can be expected from a heavy target barrel.
This is one of the reasons many people stick to one load in a given rifle. The rifle I had this problem with was a brno 30 06. I have´nt had this problem since but, the theory makes sense to me.
boet

Yep, more than once, and in different rifles and chamberings. It's not uncommon for different bullets of the same weight to have varying points of impact, left, right, up or down when propelled by the identical powder charge.

My 7 Mag will group different 140 grain bullets in different groups, some of them 5 inches apart. Even with every other variable like the powder charge, primer, over all length, etc. exactly the same.

Thank you everyone for your explanations, I thought I was going bonkers for a minute!!! This is the first time I noticed this.

Cheers,

Mo

It happens a lot! IMHO boet has the right answer. roger

Seems like it is pretty normal with a sporter weight barrel. Heavy barrels seems to eliminate most of it.

I also think Boet has the right answer in regards to sticking with one bullet, one load... however, the bullets that give me the best groups are the Barnes TSX!!! Not a cheap bullet by any means since I shoot a least once a week!!!

quote:

Originally posted by Enigma:
Hello to you all,

I just noticed something very strange at the range the other day. I was shooting some Barnes 270gr TSX at 100yrds when I noticed that I was grouping 3 inches left of center. I thought it was my scope going bonkers, but I decided to fire some 260gr Accubonds to check it. The Accubonds grouped dead center, so did the 270gr Hornady SP. I shot some TSX again, and same thing, they all grouped 3 inches left of center... Anyone else have this happen to them???

Thanks,

Mo

quote:

Originally posted by boet:
Enigma
Yes, I´ve had this problem and it was explained to me as follows :
As the bullet engraves the rifeling and speeds down the barrel, the end of the barrel describes a circle unseen to the naked eye, Different bullet weights at different velocities can be expected to leave the barrel at differing points on this circle thus, causing them to land left or right of centre. A fluted or hexagonal barrel is supposed to reduce this effect, giving a similar result to what can be expected from a heavy target barrel.
This is one of the reasons many people stick to one load in a given rifle. The rifle I had this problem with was a brno 30 06. I have´nt had this problem since but, the theory makes sense to me.
boet

Ins't that what is called "barrel whip" and sometimes (incorrectly) "harmonic vibrations"?

Lost Sheep (Larry)

quote:

.... and sometimes (incorrectly) "harmonic vibrations"?

OK..... I have wondered about that. Is that like saying "quad bike"?

Enigma, you might try changing your powder charge to bring your groups closer together. (Maybe try to get the regular loads to group closer to your TSX loads - cheaper). It would be interesting to chrono those different bullet loads.

The bullet is just one component of the load. However, it is the component we are most critical of because it is the only thing we can effectively judge. It is the component that actually strikes our intended target. Changing any one component, or a combination of components, can drastically affect the results.

I always start with a clean barrel when changing any load or individual component. The primer, powder weight or even changing the powder lots can have a big effect on the accuracy.

Personally, I use the Barnes bullets almost exclusively. I try to work my loads to fit the bullet I intend to use. Most of the time this works, but not always. Some rifles just will not satisfactorily shoot certain load combinations. But, almost all rifles will shoot one or more loads very well. The fun? is trying to find that load. When you do, it's a really good day!

If the Barnes are grouping well but they are just off your point of aim, I would just make a scope adjustment and go kill something!

Bull1

quote:

Originally posted by bartsche:
It happens a lot! IMHO boet has the right answer. roger

I agree. Bullets of different weight or even shape will leave the muzzle at a diffrent point in its' vibration pattern, and thus strike at a different point on the target. Some individual rifles are much worse about this than others, and there are numerous factors that can influence this, such as bullet weight, powder type, and even barrel length, shape, bedding, etc.

As far as I know, there really isn't much you can do to a give rifle to stop this effect.....

This is one of the reasons for the advice "when hunting, use the ammo that you have zeroed your rifle for..."(Yes, there are some who don't adhere to this rule!!)

quote:

.... As far as I know, there really isn't much you can do to a give rifle to stop this effect.....

My gunsmith uncle did an experiment in which he trimmed small amounts off the muzzle until that rifle grouped two bullet weights to the same POI. He was using factory ammo and only two loadings.

My hornet groups a Hornady SP 60gr load to the same POI as a Sierra SMP 55gr load. Changing powder charge does not seem to change POI much. But changing seating method does i.e. neck tension versus no neck tension.

All the time. It's not uncommon at all to see a pretty good shift in POI when switching to a vastly diff. bullet. IMO, it's a rare rifle that holds all it's loads to the same POI.

quote:

Originally posted by boet:
...As the bullet engraves the rifeling and speeds down the barrel, the end of the barrel describes a circle unseen to the naked eye, Different bullet weights at different velocities can be expected to leave the barrel at differing points on this circle thus, causing them to land left or right of centre. ...

The above is real close to what is happening. However, the muzzle is actually moving in a pattern similar to an Elongated Figure 8, or an ∞ Infinity Sign. And it can rotate to any randomly skewed angle.

This is easier to understand if a person does their Load Development with the never improved upon Creighton Audette Load Development Method, because you can see the changing movement of the Bullet Impact on the Target. The movement can be in any direction as the Load increases.

As the Barrel Oscillation is approaching the Apogee or the Perigee,(a Harmonic Node) the muzzle nearly Stops and then reverses its direction. At the point where the muzzle is nearly Stopped, is the point where you will locate the Harmonic Node which creates the nice tight Bullet Impact Clusters we all desire.

As the muzzle passes through the cross-over point in the middle of the Elongated Figure 8, the muzzle is traveling at the fastest speed within the Oscillation. When either Randomly Picked or Developed Loads have the Bullets making Exit from the muzzle in this situation it can be seen on Target as very w-i-d-e Random Patterns.
-----

Changes in Components(even changing Lots of the same Component) and changes in the Bore Condition will create a change in the Oscillation which causes the Harmonic Node to shift. It might tighten the Group slightly, or it might cause it to widen.

quote:

.... moving in a pattern similar to an Elongated Figure 8, or an ∞ Infinity Sign. And it can rotate to any randomly skewed angle.

Ah-ha .... That explains those slanting groups I sometimes get! I suppose they can shift from slanting to vertical to horizontal? Thanks Hot Core.

Most of the barrel movement takes place after the bullet leves the muzzle. Vaughns "Accuracy Facts" goes into this in detail.
Good Luck!

quote:

Originally posted by 303Guy:
... I suppose they can shift from slanting to vertical to harizontal? ...

Hey 303Guy, Yes that is possible, but normally the string moves up and right or left. Just can't count on it doing that all the time though because occasionally it will move down and left or right.

There are multiple types of Stresses on the Barrel during the firing sequence which cause this movement. Some are easy to understand and some require a bit of thinking to understand how they effect the barrel movement.

The Oscillation of the Rotational Torque created by the Bullet wanting to go straight while the Rifling is imparting a Spin to it is what causes the Circular movement to become the Elongated Figure 8 pattern.

The folks who mentioned the HEAVY barrels help Dampen the Oscillations are correct. This is particularly important where a person is interested in a large amount of Bullets going to the same place in a short amount of time - BenchRest shooters would be an example.

In the case of Hunters, a thin barrel has Light weight advantages which normally do not need a bunch of Bullets sent in a short amount of time. So, as long as a 2-shot or perhaps 3-shot group is tight, the additional shots don't mean a thing. In fact, if the animal is not dead after 3-shots, there is some problem which really needs to be addressed.

I prefer cumulative 1-shot groups on the same Target to Finalize a new Load. Each shot from a pristine clean and lightly lubed Bore. Because that is the condition my Bore will be in when I am Hunting. If it shoots nice tight groups in that situation(all near a Harmonic Node), it is time to move on to Position Shooting and forget the Bench.

Best of luck to you.

While testing for repeatabilty by changing powder weight by .5 gr. at a time we not only saw group size change but we also notice up to an inch change in point of impact at 100yds..

This allowing what we thought a reasonable time between shots to allow barrel cooling.It would indicate that although the bullet selection is the primary culprit in this happening, powder and the amount there of are contributing factors also. roger

Thanks for the very interesting info Hot Core.

I also need to take the effects of wind into account. I fired a few shots at a target 200m along a steep sided gully with a shear cliff face at the end. The wind was farely strong, blowing along the gully and up the cliff face. Those shots hit high. They should have landed 4 inches low.