Neck tension vs. FRTS

[Sgt. Brumbaugh]

With the advent of the AMP press or the KM arbor press with force pack I don't pay as much attention to the mathematical number of neck tension as I used to and instead rely on FRTS (force required to seat). As anyone with an AMP press or the KM with a force pack can tell you that many things can affect the FRTS and cause it to vary greatly- all the while having the exact same mathematical number of neck tension.

Does anyone have / run both the AMP and the KM with the force pack and think the AMP is worth the cost over the KM?

 

[Alex Wheeler]

The mathmatical number matters more.

 

[Chaotik]

Seating force is not a measure of neck tension.

 

[wkdickinson]

Seating force is not a measure of neck tension.

Maybe not, but it is a measurement of seating (and theoretically, required "release") forces, which is what we are striving for with neck tension. Personally, I have always wondered how much of a part "friction" inside the neck plays in bullet seating force measurements. Just last week I purchased a new K&M w/force pack and a Wilson seating die for my 6BRA. My first experiments will be to try and answer that question.

 

[Chaotik]

Seating force reflects the friction in the neck, and is a measurement of that. It does not directly reflect the "grip" or tension on a static bullet in the neck. There is no commercially available method or tool to measure the hoop tension of the neck.
Does the bullet, when the cartridge is fired, slide out of the neck while maintaining contact with the inside of the neck? Or does bullet release from the neck occur before any movement of the bullet out of the neck? It's an interesting question.
In my testing I have never been able to find a correlation between seating force and projectile velocity or impact on the target. But your experience may be different.

 

[wkdickinson]

Seating force reflects the friction in the neck, and is a measurement of that. It does not directly reflect the "grip" or tension on a static bullet in the neck. There is no commercially available method or tool to measure the hoop tension of the neck.
Does the bullet, when the cartridge is fired, slide out of the neck while maintaining contact with the inside of the neck? Or does bullet release from the neck occur before any movement of the bullet out of the neck? It's an interesting question.
In my testing I have never been able to find a correlation between seating force and projectile velocity or impact on the target. But your experience may be different.

I agree, that neck tension can't be measured, it can only be calculated (bullet dia. - inside neck dia.). However, logic tells us that the greater the difference between the two, i.e., "neck tension", more friction and consequently more force will be required to seat (or release) the bullet. My point was there are also other source of "neck friction" such as carbon and/or surface smoothness. I wonder how much influence the consistency of those other source of friction have with regard to the variance of seat forced required round to round?

If your thought about the neck expanding before the bullet moves is actually what happened, then it kind of makes the whole neck tension argument moot.

 

[Bottom Fodder]

Not disagreeing with any, just asking if seating force has nothing to do with bullet release then way do need to know that precisely of seating force that you need a pressure gauge?

 

[L.Sherm]

My guess is consistency

 

[VA_XTC_Shooter]

If your thought about the neck expanding before the bullet moves is actually what happened, then it kind of makes the whole neck tension argument momoot.

How is it moot? The more "neck tension" the more pressure required to expand the neck and release the bullet, delaying bullet movement.
The force gage measures friction to seat a bullet, which is irrelevant, the bullet encounters friction in the bore, not the case.
As mentioned above, pressure in case expands neck to release bullet, then bullet engages lands increasing pressure for an instant, then friction begins.

 

[Straightshooter1]

I agree, that neck tension can't be measured, it can only be calculated (bullet dia. - inside neck dia.). However, logic tells us that the greater the difference between the two, i.e., "neck tension", more friction and consequently more force will be required to seat (or release) the bullet. My point was there are also other source of "neck friction" such as carbon and/or surface smoothness. I wonder how much influence the consistency of those other source of friction have with regard to the variance of seat forced required round to round?

If your thought about the neck expanding before the bullet moves is actually what happened, then it kind of makes the whole neck tension argument moot.

When I look at the numbers, here's what I see . . .

The bullet does start to move before the neck expands. It doesn't take much pressure to start the bullet moving and the amount of pressure that "starts" the bullet moving is less than it take to expand the neck. Therefore the neck start to expand after the bullet starts moving (we're talking about a time period like in is small number of milliseconds, or fraction of one). Once the pressure builds to start the neck expansion, the bullet is usually far from becoming fully engraved into the bore or even clearing out of the case all together and before it does, the expansion of the neck is allowing (how fast and how much) there's an amount of blowby from the powder igniting to influence the way the pressure builds. Neck tension has a significant influence on how much blowby occurs before the bullet is fully engraved.

And yes, there are other influences involved with the interference between the case neck and the bearing surface affecting the timing of this blowby issue. "Neck tension" (how much pressure the neck is exerting on the bearing surface) is only part of the equation. . . but a significant part.

 

[Sgt. Brumbaugh]

The mathmatical number matters more.

I don't make it a point to argue with guys like you, but in this case I will debate you.

I developed my opinion when I was loading for a 338 LAI I had. It was my ELR light rifle and was a reliable 1/3 MOA rifle. I had several firings on some brass and decided to anneal the them. The FRTS went from 50 lbs down to 25 after being annealed (same bushings, mandrel, etc) and accuracy fell apart. I ran a smaller bushing to get the FRTS back up to 50 (same mandrel, so the "number" was the same) accuracy came back and stayed back.

I know a .364 bushing and a .336 mandrel will have much different FRTS than a .367 bushing and the same mandrel. I would argue the effective neck tension is much different even though the "number" is the same. Then add in neo lube, etc, and things change again.

I think it is pretty obvious that the bullet moves before the neck swells to release (maybe not if jammed, but certainly when jumping) if that is the case, the bullet is essentially overcoming the friction and tension all at once. But I think the more reliable number to tune off of would be FRTS.

 

[Bottom Fodder]

I don't make it a point to argue with guys like you, but in this case I will debate you.

I developed my opinion when I was loading for a 338 LAI I had. It was my ELR light rifle and was a reliable 1/3 MOA rifle. I had several firings on some brass and decided to anneal the them. The FRTS went from 50 lbs down to 25 after being annealed (same bushings, mandrel, etc) and accuracy fell apart. I ran a smaller bushing to get the FRTS back up to 50 (same mandrel, so the "number" was the same) accuracy came back and stayed back.

I know a .364 bushing and a .336 mandrel will have much different FRTS than a .367 bushing and the same mandrel. I would argue the effective neck tension is much different even though the "number" is the same. Then add in neo lube, etc, and things change again.

I think it is pretty obvious that the bullet moves before the neck swells to release (maybe not if jammed, but certainly when jumping) if that is the case, the bullet is essentially overcoming the friction and tension all at once. But I think the more reliable number to tune off of would be FRTS.

Not disagreeing but just asking in your case higher pressure increased your accuracy and annealing hurt , I’ve seen this in pistol cartridges

 

[L.Sherm]

What if you dont use a mandrel?

 

[Wild Bill IV]

Seating force reflects the friction in the neck, and is a measurement of that. It does not directly reflect the "grip" or tension on a static bullet in the neck. There is no commercially available method or tool to measure the hoop tension of the neck.
Does the bullet, when the cartridge is fired, slide out of the neck while maintaining contact with the inside of the neck? Or does bullet release from the neck occur before any movement of the bullet out of the neck? It's an interesting question.
In my testing I have never been able to find a correlation between seating force and projectile velocity or impact on the target. But your experience may be different.

Finally, someone who understands the 2 frictional forces!!
Kinetic Friction, (frictional forces between two bodies in motion), and Static friction(frictional force between 2 bodies at rest, velocity=0). Static Friction > and/or = Kinetic Friction!!

"PHYSICS IS BASED ON PRINCIPLES, NOT ANALOGY", ELON MUSK!!!!!

HOWEVER, I disagree with the statement that Static Friction can not be measured!! As an Industrial Physist, with 105 credit hours of Pure Science, It can be determined with the OPs equipment!!

The Static Friction can be determined by stopping the seating depth a few thousands shy of the desired seating depth!! At that point, all motion is zero or STATIC!! Readjust the seating die to the desired depth and use the load cell data recording the Static BREAKING Forces (Static forces are the Static Tension Force in the neck which is equal to the opposing Static Compression Force of the bullet). YES, you have to use BASIC PRINCIPLES, also called the FUNDAMENTALS of Physics using Newton's Laws of Motion!! These Fundamentals are:
Bodies at rest, tends to stay at rest, unless a force acts on those bodies!! The Static State!!
For Every Force, there is an equal but opposite Force!! The Tension Force = the negative of the opposing Compression Force! Thus the 2 forces are balanced or Static!!

An understanding of Principles of Pysics leads me to a conclusion!! The uniformity of the Breaking Force is more Critical to Accuracy than uniformity of Seating Force!!! Another Fundamental of Physics and Engineering!!
STATIC FRICTION IS GREATER THAN OR EQUAL TO KINETIC FRICTION!!! In other words, who cares about kinetic friction once the static friction is over come by the accelerating pressure buildup behind the accelerating bullet which is now in motion or DYNAMIC!!!

Anyone opposing these Basic Principles does not understand them, and will argue using Analogies!!!

 

[J.d. Popkes]

My guess is consistency

In my opinion. Knowing WHAT works is more important than WHY it works. Find what works and figure out how to consistently replicate it.

Why are boobs cool, who knows, just are.

 

[Wild Bill IV]

The mathmatical number matters more.

But are those numbers the numbers we should really be looking at? See my post above this Reply!!

And, when annealing, you have to wait for grain growth. I read a master's thesis where the intern did a study on the annealing process at Norma!! He pulled hundreds of samples for four days for 308 and 300 win cases in various 10 steps (308) and 11 steps (300 win) annealed stages of formation for four days!! He conducted destructive hardness testing and micron microscope photography of the grain structure and their boundary regions!!!

His data concluded that one day old annealed cases were softer than the previous 3 days samples but the grain size and hardness are not directed related!! To truly get accurate data, annealed cases need to set for two days for proper grain growth and consistent hardness!!!

 

[JFrank]

But are those numbers the numbers we should really be looking at?

My targets say the dimensional difference has more value than friction.

 

[gmr4]

In my opinion. Knowing WHAT works is more important than WHY it works. Find what works and figure out how to consistently replicate it.

Why are boobs cool, who knows, just are.

I agree with this totally. Sizing necks - bushings and mandrells, annealing, cleaning, brushing, lube no lube. All of these processes change the release force / neck tension / bullet grip… whatever sizes and combination of actions works consistently counts.

 

[WSnyder]

Why are boobs cool, who knows, just are.