Velocity "honey nodes/velocities" in typical bench gun barrels for 6mm

[Bradley Walker]

This is not meant to be a statement of fact. Please feel free to correct me, if you feel I am full of beans:

So, after reading and reading and reading and reading.... Watching videos of champions on Youtube, and generally looking everywhere I can it appears that the "real" science behind getting a "tuned load" in your typcial BR gun is really just finding the "honey node velocity"...

These are velocities are typical for your 105-108 bullets. So the "honey nodes" appear to be at

2720-2750
2820-2850
2920-2950
3020-3050

1. These "honey" numbers don't care what the rifle is or even what the cartidge is (assuming the barrel is a LV, HV or straight "typcially quality benchrest rifle" with a barrel of 24-30 inches)....

2. The powder you use is simply dependent upon which node you choose to use. Keeping the velocity variation low at the "node" velocity locations seems to be the only other factor to look for in powder choice (aside from temperature sensitivity). So, you have to get a powder that has low ES at youir chosen node.... that is about it.... I assume this ES has lots to do with the primer and powder density %.

3. Seating depth is simply a method for tuning the velocity (for the most part). The bullet out further lowers the velocity, the bullet in further raises the velocity. I am sure there are bullets that shoot better "jammed" or "jumped", but jamming still makes no sense to me, and you have to chase the lands... and that ends up changing the velocity.

Does anyone know the node velocities for the 80 gr bullets?

Does anyone know the nodes for your typcial 6 PPC 200 yard, 68 grain bullet nodes?

 

[Bradley Walker]

http://www.ozfclass.com/articles/1/psm_2005_03.html

 

[lpreddick]

you need to read chris long's paper on the shock wave theory of rifle accuracy. you will need to read it several times and realize what he is describing...a shock wave is created at the moment of powder sublimation and this wave (called a donut) bounces back and forth from chamber to muzzel several times before bullet exit. seating depth determines when the bullet exits the muzzel. exit time when the wave is at the chamber produces the "accuracy node". powder charge changes speed up or slows down the bullet to achieve the same relatonship. the latter is more difficult compared to seating depth changes...often .005-.010 thous will change a 3/8 in group to one hole. i chased powder charge changes for years but now find accuracy nodes quickly using the appropriate powder/bullet combination and seating depth adjustments. try it , you will like it.

 

[Bradley Walker]

Ive read that several times. Of course it's just a theory. There are several similar theories...

It also does not disagree with any of the points I made above. I think it would find that the seating depth change you speak of simply changes the velocity in the exact same manner as changing the powder. Thus moving the velocity into one of the velocity nodes that appears to be used by everyone that ever finds a honey load in 6mm.

Even the bullet designs that everyone assumed needed to be jammed for example, turns out they don't.

 

[lpreddick]

my current chronograph(the other two got shot) can't accurately measure velocity changes when i seat a bullet .005 thous or more deeper or longer, but the holes in the paper definitely change not only in configuration but interestingly, in location. the cluster as it tightens will sometimes move a 1/4 in left or right more than up or down. since barrel time for a bullet is measured in milliseconds, starting a bullet .005 thou or more deeper in a case or further out will change it's arrival time at the muzzel, hopefully when the shock wave is at the chamber. increasing powder charges by .2 gr(small case like 6br) usually registers an increase on my chrony. .3 or.4 will definitely do so. these slightly increased charges will on occasion tighten a group as long as the seating depth stays the same...this seem to be the basis for the "ladder" testing procedure. seating depth changes, almost limitless, are much less likely to get you in trouble with excessive pressures as compared to powder charge increases, which have narrow ranges...been there, done that(ackley cases are notorious for pressure spikes suddenly with slight powder increases). anyway, the pursuit of the one hole group is fun, especially when you tinker with the very few variables we can affect.

 

[Bradley Walker]

my current chronograph(the other two got shot) can't accurately measure velocity changes when i seat a bullet .005 thous or more deeper or longer, but the holes in the paper definitely change not only in configuration but interestingly, in location. the cluster as it tightens will sometimes move a 1/4 in left or right more than up or down.

Really?

Very, very intersting... So, that would speak to barrel timing. I would have thought seating would be easily seen like powder. Tells you what I know!!!

I am very excited to get the chrono back out...

 

[Bradley Walker]

This isi the type of thing I was talking about. This was verified by the load tuning video with Jack Neary on Youtube. I believe you will find this is how the top competitive guys do it "for real".

"PPC Load Tuning Tips – by Gene Beggs

Assuming a 6ppc with a LV contour 22 inches long shooting 68 grain bullets with N133 powder, the tuning nodes or "sweet spots" as some shooters call them, appear at 120 fps intervals. Or, expressed in terms of powder charge, 1.2 grain intervals. Most benchrest rifles behave in a similar fashion. You can prove this with your rifle by shooting several three shot groups beginning at 27 grains and increasing in .3 grain intervals up to a max of 30 grains. If the rifle is in tune and shooting dots at 27 grains, it will begin to show vertical at 27.3 grains and will be completely out of tune at 27.6 grains. It will come back together at 28.2 grains and will again be completely out of tune at 28.8, the last node appearing at 30 grains.

Once the rifle is in tune, make a note of the density altitude and charge weight. If DA increases by 500 feet, decrease the load by .3 grains and vice versa.

If DA goes up decrease the load; if DA decreases increase the load. The formula is .3 grains per 500 feet DA. Since temperature is the main reason for changes in DA you can accomplish the same thing by using only a thermometer. The ratio is .3 grains per five degrees F

On a Culver type measure, each full number represents .6 grains of the powders we normally use in the 6PPC, i.e., N133, H322, Benchmark, etc. Make your adjustments in .3 grain increments which is half a number, which in turn equates to 30 fps change in muzzle velocity.

You must decide whether you will tune with the powder charge or a moveable tuner; you should not try to mix the two. When tuning with a tuner, you never change the load."

Interestingly, to me this makes perfect sense.

DA up means there is more oxygen in the air so less fuel is required to reach the same explosion.

DA down means there is less oxygen in the air so more fuel is required.

This is EXACTLY the same way an ENGINE IS TUNED!!!

I think if you look, all of the popular 6BR loads top node hover right around 30 grains (100% case capacity)... So if the powder is appropriate for the bullet weight used, the intervals between the nodes are still going to be right at 1.2 grains. I think the BR and PPC are close enough in case capacity the same rules apply.

 

[Alex Wheeler]

This isi the type of thing I was talking about. This was verified by the load tuning video with Jack Neary on Youtube. I believe you will find this is how the top competitive guys do it "for real".

"PPC Load Tuning Tips – by Gene Beggs

Assuming a 6ppc with a LV contour 22 inches long shooting 68 grain bullets with N133 powder, the tuning nodes or "sweet spots" as some shooters call them, appear at 120 fps intervals. Or, expressed in terms of powder charge, 1.2 grain intervals. Most benchrest rifles behave in a similar fashion. You can prove this with your rifle by shooting several three shot groups beginning at 27 grains and increasing in .3 grain intervals up to a max of 30 grains. If the rifle is in tune and shooting dots at 27 grains, it will begin to show vertical at 27.3 grains and will be completely out of tune at 27.6 grains. It will come back together at 28.2 grains and will again be completely out of tune at 28.8, the last node appearing at 30 grains.

Once the rifle is in tune, make a note of the density altitude and charge weight. If DA increases by 500 feet, decrease the load by .3 grains and vice versa.

If DA goes up decrease the load; if DA decreases increase the load. The formula is .3 grains per 500 feet DA. Since temperature is the main reason for changes in DA you can accomplish the same thing by using only a thermometer. The ratio is .3 grains per five degrees F

On a Culver type measure, each full number represents .6 grains of the powders we normally use in the 6PPC, i.e., N133, H322, Benchmark, etc. Make your adjustments in .3 grain increments which is half a number, which in turn equates to 30 fps change in muzzle velocity.

You must decide whether you will tune with the powder charge or a moveable tuner; you should not try to mix the two. When tuning with a tuner, you never change the load."

Interestingly, to me this makes perfect sense.

DA up means there is more oxygen in the air so less fuel is required to reach the same explosion.

DA down means there is less oxygen in the air so more fuel is required.

This is EXACTLY the same way an ENGINE IS TUNED!!!

I think if you look, all of the popular 6BR loads top node hover right around 30 grains (100% case capacity)... So if the powder is appropriate for the bullet weight used, the intervals between the nodes are still going to be right at 1.2 grains. I think the BR and PPC are close enough in case capacity the same rules apply.

Actually The way we tune engines is just the opposite. Denser air, more oxygen, more fuel, to keep from going lean.
Alex

 

[Bradley Walker]

I think they are completely separate factors.

If they were the same, you would need MORE powder in higher density to reacj the same velocity because the air is thicker.

A bullet would slow faster in high DA in flight.

 

[Bradley Walker]

A cartridge is sealed the moment a bullet is seated. In the case of bullets being seated into the lands, the cartridge & chamber area remain sealed until the bullet exits the barrel.
So how do you figure changes in oxygen content affect the way the propellant is burnt?

Hmmmm...

 

[Bradley Walker]

A cartridge is sealed the moment a bullet is seated. In the case of bullets being seated into the lands, the cartridge & chamber area remain sealed until the bullet exits the barrel.
So how do you figure changes in oxygen content affect the way the propellant is burnt?

Could you please explain what Mr. Beggs was saying he was "tuning" if what you say is true? I am curious...

 

[Bradley Walker]

http://benchrest.com/showthread.php?69008-Gene-beggs-makes-big-mistake-!!!

 

[Bradley Walker]

I never said anything POI.

Tuning, in this case is just finding the dead spot in the harmonic. Or when the tip of barrel changes direction.

In other words all the bullets want to go through the same hole.

 

[Erik Cortina]

Bradly Walker, you say jamming into the lands makes no sense to you because you have to chase the lands. So, when you jump, there is no need to chase the lands?

Thanks.

 

[Bradley Walker]

Bradly Walker, you say jamming into the lands makes no sense to you because you have to chase the lands. So, when you jump, there is no need to chase the lands?

Thanks.

I don't think as much. You are not planning on the pressure spike as part of the pressure tuning.

This is a good question really. One that I do not claim to have a high level answer. I know one of the 600 yard record holders admitted he set the seating depth for his rifle when it was new and never changed it even though the lands had eroded .080"? The gun still hammered.

My kreiger barreled space gun used to shoot amazing groups with factory length ammo. I would think planning for jump from the beginning would make the location of the lands less important.

I will study it more.

 

[Erik Cortina]

Do you realize that there are three bullet positions in relation to lands right?
There is jump, in the lands, and jam.

 

[Bradley Walker]

Yes.

Jump
Itl means the bullet is roughing the the lands.
Jam the bolt is seating the bullet.

Why?

 

[Erik Cortina]

Because you said nothing about bullet in the lands, you only made reference to jump and jam. So, when bullet is in the lands, do you also rely on initial pressure spike as part of tuning?

 

[Bradley Walker]

That is the typical thought yes. Of course others say its time in the barrel. So maybe it's distance!!

 

[Erik Cortina]

So, if seating depth when you jump has little to no effect, then all guns should hammer with bullet jump regardless of jump distance?