Vertical Dispersion: Flat spots on the MV ladder test are meaningless

[Tarmacshooter]

I can’t disagree with your response. My contention is and is held by many others is that a ladder test of .2 increments is the start of the tuning process. It’s not the end all be all.

I’m to the point of my tuning and shooting career that I’m chasing sub 1/2 MOA over 20 to 24 shots for mid range.

@BartsBullets F-Class.

 

[davidjoe]

I see nothing supported in the claims.
For one, powder burn rate is tied to pressure. It feeds on itself. This is well known for over 100yrs.
2nd, I would expect to see MVs directly affected by barrel vibrations in your test, to support your claims.

I wish someone would reconcile why there are velocity flat spots where powder continues to increase.

While group size might be explained by barrel harmonics, velocity at the muzzle, should increase as pressure increases.

We recognize that at some pressure level, brass resistance gives out, and like a hydraulic press deforming an object, pressure must decline somewhat at that moment.

The other interplay that comes to mind is the bullet’s entrance to the chamber, the lands and its obturation. However, V flat spots here while pressure increases, needs the some elaboration doesn’t it? If someone said a 16 pound shot put can reach the same distance within a window of different amounts of energy exerted, an Olympian might beg their pardon.

If the idea is that powder pressure does not always increase predictably, despite there being more of it burning, the explanation for that phenomenon is something I’d sure be interested to know.

 

[LVLAaron]

I wish someone would reconcile why there are velocity flat spots where powder continues to increase.

While group size might be explained by barrel harmonics, velocity at the muzzle, should increase as pressure increases.

We recognize that at some pressure level, brass resistance gives out, and like a hydraulic press deforming an object, pressure must decline somewhat at that moment.

The other interplay that comes to mind is the bullet’s entrance to the chamber, the lands and its obturation. However, V flat spots here while pressure increases, needs the some elaboration doesn’t it? If someone said a 16 pound shot put can reach the same distance within a window of different amounts of energy exerted, an Olympian might beg their pardon.

If the idea is that powder pressure does not always increase predictably, despite there being more of it burning, the explanation for that phenomenon is something I’d sure be interested to know.

One of lifes many unsolved mysteries! - I've done OCW and ladders. I always did OCW until I figured out what the velocity ladders are telling me. Most importantly they have to be repeatable. I wont take a new gun, shoot one ladder and trust it, at all.

Like Bart said, we're tuning for different things. I want to tune once or twice all summer and shoot. If it's a 1/4-1/3 minute gun, I'm going to be happy and it can shoot clean targets.

1/4 minute in SR bench might as well be a 12g shotgun

Personally I do see correlation between velocity flat spots and a load that I can tune to do what I need the gun to do.

Bart, come up to borden (just north of Louisville) and we'll use each others methods and see where we end up.

 

[LRPV]

As @LVLAaron mentioned, if you tune the rifle correctly, it will shoot no matter what the temp (within reason) and humidity is. And as long as elevation is similar. And if it doesn’t adjusting seating depth can quickly get it back very close to the previous accuracy.

I respectfully disagree

Jim, I have done exactly this from one side of the country to the other. I'm not trying to say that it will be the very best tune at every given minute of the day or whatever but I've been successful at 600 and 1k benchrest using this method. I have even done it with Varget of all powders and a Dasher of all cases.

 

[Clancy]

I don’t think ladders are useless. The best 1,000 yard shooters in the world use them.

I think mall ninjas with labradars thinking if they get 3 shots within 20 fps of each other that their load development is done is useless.

I thought I made that clear but I suppose I didn’t.

 

[JFrank]

@LRPV
Jason I really appreciate your input , my disagreement is in the use of seating adjustments to correct point of impact /vertical dispersion that may pop up from altitude or climate changes. I really don’t see the shifting from depth changes other then shape of groups. I’m still learning this stuff but that’s what I’m seeing from my perspective.

 

[davidjoe]

One of lifes many unsolved mysteries! - I've done OCW and ladders. I always did OCW until I figured out what the velocity ladders are telling me. Most importantly they have to be repeatable. I wont take a new gun, shoot one ladder and trust it, at all.

Yes, and while discerning finite details with the eye is admittedly difficult, signs of pressure on fired casings and on primers don’t tend to indicate that there are any places where a warm load does not continue to get “warmer” when more powder is added.

 

[6bra1k]

i think the writer is completely out of OUR element. he has not defined a goal. we shoot f class and long range br. we shoot small 5/10/20 shot groups at 600-1000 yards( no account for short range fclass). no gun nor target he has shown/mentioned is in this class.
if you shoot a "ladder" three times, that is GROUP shooting period. look at every target posted by a triple ladder and it clearly shows THREE SHOT GROUPS CIRCLED.
i am done with this thread. a real problem with poorly defined goals.

 

[Tarmacshooter]

again, we’ve been trolled. Guy drops a post with dubious claims and data, argument ensues. He sits back and laughs.

 

[Beiruty]

I wish someone would reconcile why there are velocity flat spots where powder continues to increase.

While group size might be explained by barrel harmonics, velocity at the muzzle, should increase as pressure increases.

We recognize that at some pressure level, brass resistance gives out, and like a hydraulic press deforming an object, pressure must decline somewhat at that moment.

The other interplay that comes to mind is the bullet’s entrance to the chamber, the lands and its obturation. However, V flat spots here while pressure increases, needs the some elaboration doesn’t it? If someone said a 16 pound shot put can reach the same distance within a window of different amounts of energy exerted, an Olympian might beg their pardon.

If the idea is that powder pressure does not always increase predictably, despite there being more of it burning, the explanation for that phenomenon is something I’d sure be interested to know.

It is still barrel harmonics. Or, let us say, assuming all other factors stayed consistently the same except the powder charge.

Here is my explanation:

The barrel would undergo a series of constriction nodes along it is length due to the explosion shock waves. The number of standing-wave constriction node can vary depending on the barrel length, bullet used, powder burning rate, powder charge and primer ignition initial pressure.

The resistance of bullet/barrel interface is assumed to be constant all along the barrel. However, this is not exactly true. The actual resistance of the barrel/bullet interface has to include the dynamic resistance introduced with the constriction nodes all along the barrel length.

So, if the powder charge has been increased, but the MV stayed the same (assuming all other factors are still the same) that means the resistance of the bullet/barrel has increased. That means the number of constriction nodes all along the barrel length has increased.

Using the GRTools, increasing the bullet/barrel interface resistance, can be shown to reduce the MV while increasing the maximum pressure of the load.

In Summary:
1) Powder charge increases (load n+1)
2) Number of constriction nodes increases from load n
3) Dynamic barrel/bullet interface resistance increases from load n
4) Maximum Pressure increases from load n and expected n+1 load
5) MV would decrease from expected load n+1 and get closer to MV of load n

I hope this is clear enough. If not, please ask questions.

 

[Beiruty]

again, we’ve been trolled. Guy drops a post with dubious claims and data, argument ensues. He sits back and laughs.

I have a life and I do have a full time job. Please cut me a slack, I do not work for your Mr. TarnacShooter.

 

[davidjoe]

It is still barrel harmonics. Or, let us say, assuming all other factors stayed consistently the same except the powder charge.

Here is my explanation:

The barrel would undergo a series of constriction nodes along it is length due to the explosion shock waves. The number of standing-wave constriction node can vary depending on the barrel length, bullet used, powder burning rate, powder charge and primer ignition initial pressure.

The resistance of bullet/barrel interface is assumed to be constant all along the barrel. However, this is not exactly true. The actual resistance of the barrel/bullet interface has to include the dynamic resistance introduced with the constriction nodes all along the barrel length.

So, if the powder charge has been increased, but the MV stayed the same (assuming all other factors are still the same) that means the resistance of the bullet/barrel has increased. That means the number of constriction nodes all along the barrel length has increased.

Using the GRTools, increasing the bullet/barrel interface resistance, can be shown to reduce the MV while increasing the maximum pressure of the load.

In Summary:
1) Powder charge increases (load n+1)
2) Number of constriction nodes increases from load n
3) Dynamic barrel/bullet interface resistance increases from load n
4) Maximum Pressure of the increases from load n and expected n+1
5) MV would decrease from expected load n+1 and get closer to MV of load n

I hope this is clear enough. If not, please ask questions.

Constriction nodes are new to me. I admit it’s hard to disagree with the idea, in principle - it’s beyond doubt that a 1.0000” hole through two feet of ballistic gelatin that is given a hard slap at one end, will vary its diameter many times at the same location.

 

[CA_Shooter]

It is still barrel harmonics. Or, let us say, assuming all other factors stayed consistently the same except the powder charge.

Here is my explanation:

The barrel would undergo a series of constriction nodes along it is length due to the explosion shock waves. The number of standing-wave constriction node can vary depending on the barrel length, bullet used, powder burning rate, powder charge and primer ignition initial pressure.

The resistance of bullet/barrel interface is assumed to be constant all along the barrel. However, this is not exactly true. The actual resistance of the barrel/bullet interface has to include the dynamic resistance introduced with the constriction nodes all along the barrel length.

So, if the powder charge has been increased, but the MV stayed the same (assuming all other factors are still the same) that means the resistance of the bullet/barrel has increased. That means the number of constriction nodes all along the barrel length has increased.

Using the GRTools, increasing the bullet/barrel interface resistance, can be shown to reduce the MV while increasing the maximum pressure of the load.

In Summary:
1) Powder charge increases (load n+1)
2) Number of constriction nodes increases from load n
3) Dynamic barrel/bullet interface resistance increases from load n
4) Maximum Pressure increases from load n and expected n+1 load
5) MV would decrease from expected load n+1 and get closer to MV of load n

I hope this is clear enough. If not, please ask questions.

It seems there is a way to try to test what you just wrote above. However you would need to sufficiently wait in between shots to allow the barrel to cool off:

Steps:
1. Load from minimum charge to max charge in increments of .1 grains or .05 grains (better than .1). This is easily a 50 shot test
2. Shoot them over your labradar. In this scenario you would get a decent sample size
3. Plot the shots on your chart. And you should get multiple flat spots if barrel harmonics are impacting a velocity flat spot (I think that is what you meant).
4. Repeat the test 3+ times to see if the results do not change

 

[davidjoe]

Nodes being as ingrained as they are in daily experience, I do wonder if we sometimes attribute too much to them. We observed early on that spinning fan blades appear stationary at a certain speed, then again at a different speed. Feathered tires’ lives can be extended avoiding certain speeds, and we can’t march in unison on some bridges. These are indisputable whether the “why” is known or not.

In competent barrel “cut down” tests, we definitely expect to see a peak V at a certain length. We might see a couple of lengths with negligible V differences, but where the curve is steep on either the high or low end of V, we don’t expect to see flat spots at all.

If it were proposed that every so often we would see a flat spot in the curve, then the curve again, but we don’t know why, that would be very difficult to accept as valid as opposed to testing error, which is by analogy, the reason for my question.

 

[GetReal]

That depends a lot on what your accuracy requirements are. I’ve had a few days in Short Range Benchrest competition, where I didn’t have to change the load to keep a competitive tune. However that’s very rare. Most days I have to tweak my load three times before lunch to keep it shooting competitively.


Bart

I'm thinking you mean the need to change powder charges bcuz of velocity changes due to temp changes ... ?

 

[CharlieNC]

PV = nRT is like gravity. It's not a theory, it's a fact, and difficult to overcome.

 

[BartsBullets]

One of lifes many unsolved mysteries! - I've done OCW and ladders. I always did OCW until I figured out what the velocity ladders are telling me. Most importantly they have to be repeatable. I wont take a new gun, shoot one ladder and trust it, at all.

Like Bart said, we're tuning for different things. I want to tune once or twice all summer and shoot. If it's a 1/4-1/3 minute gun, I'm going to be happy and it can shoot clean targets.

1/4 minute in SR bench might as well be a 12g shotgun

Personally I do see correlation between velocity flat spots and a load that I can tune to do what I need the gun to do.

Bart, come up to borden (just north of Louisville) and we'll use each others methods and see where we end up.

@LVLAaron Lots of different roads lead to the same destination. All that matters is how it preforms when they say Commence Fire. Doesn’t matter how you get there.
You need to come down here if you want to test things out. But I’m pretty busy for the next month or so. But no one will bother us here.

Bart

 

[BartsBullets]

At Deep Creek we are working in the pits quite a bit , I would have to be part ninja to get ammunition loaded in time.

I Understand.

 

[big5ifty]

If by “Satterlee method” you mean loading one round per charge weight and looking for flat spots in the velocity graph, that is pure utter horseshit and you are only ever going to see random noise, and the results won’t replicate. You may as well use a Ouija board to pick your charge weights. Scott Satterlee doesn’t teach that anymore, by the way.

From another thread on this forum in 2020.

I am not alone.

 

[BartsBullets]

I'm thinking you mean the need to change powder charges bcuz of velocity changes due to temp changes ... ?

In general terms yes. In short range especially if the wind isn’t howling you need a perfectly tuned rifle all day. To do that you have to chase the load.

My 3 Gun Agg at the IBS Nationals (last week) was a .2167. That’s fifteen 5 shot groups at 100yds and fifteen 5 shot groups at 200yds. That’s 150 record shots and it was good for 3rd place.