Case Capacity a Question for Nosler

[steve4102]

In you new #7 manual you list "Case Holds" "XX.X gr Water"

In my experience there are two type of H20 case capacity measurements.
One being "Case Water Capacity" which is the weight of water in grains that fits in the case under the seated bullet.

The other and more useful to the handloader is "Case Water Overflow" which is how much water fits in an empty fired case, level with the mouth; no meniscus (and no bullet).

The "Overflow" method allows for the handloader to determine which headstamps have more internal capacity and which ones have less internal capacity so he/she can adjust load accordingly.

By looking at your data I would have to assume that you are using the "Water under the seated bullet" method. I say this because even thought you are using the same Nosler brass your case capacity data is different with different bullets. For example your 30-06 water capacity ranges from 59.7gr of H20 to 67.7gr of H20 with identical Nosler brass.

Am I correct in assuming you are using the weight of water in grains that fits under the seated bullet? If so why and what use is this to the average handloader?
I can tell you that on several loading forums many a handloader are confused as to what your water capacity actually means.

Take your 223 data for example, you have H20 capacity ranging from 26.5gr to 28.2gr H20. Most handloader that check internal capacity by the "Overflow method" have about 30+gr H20. They interpret your data to mean that your "Overflow capacity" is 26.5gr, therefore they must reduce their loads considerably to accommodate your reduced capacity brass.

Some clarification would be good.

Thanks
Steve

 

[steve4102]

I received a reply to my question from Nosler yesterday.

In response to your question:

That is the remaining capacity after the bullet is seated.


Have a great day,

Nosler FAQ


Their reply answered the basic question, but also left a few questions unanswered.
Why is this data included and of what use is it to the average handloader?

Anybody know why Nosler would list the grains of H20 under the seated bullet? Except for some Quickload applications I am at a loss as to what this additional data could be for for and how it benefits the average handloader.

Ideas?

 

[tddeangelo]

.......

 

[steve4102]

Just taking a flyer at this...

Capacity under the seated bullet is the "working capacity," as this is what directly affects chamber pressure. The bullet you select, and the seating depth at which you seat it, affects the internal capacity of the case. That capacity is a major factor in the pressure a load will generate, so my guess is that Nosler is using this so the reloader can see the influence of a given bullet selection on pressure.

Actually it's does not affect pressure due to case capacity in a bottle necked rifle round. In fact the longer the OAL (more room under bullet) the higher the pressure. Here is why.

From John Barness of Handloader Magazine.

Reducing OAL decreases peak pressure, for two reasons. The longer "jump" of the bullet to the rifling results in a lower peak pressure, since the bullet engraves more easily the faster it's going when it hits the rifling.

Also involved is the "progressive" burning of almost all modern rifle powders. This means the pressure increases relatively slowly from the time of ignition. Thus peak pressure occurs when the bullet beyond the barrel throat, with very slow-burning powders as much as 3-4 inches.

 

[tddeangelo]

........

 

[steve4102]

I'm curious, then, why I've generally noted increased pressure symptoms with shortened OAL, when all else remains constant (specific bullet, powder type/charge, primer, case prep, same rifle, etc)?

Don't know about your "Symptoms", but here is actual pressure tested data.

 

[tddeangelo]

........

 

[kraky1]

This comes up pretty regular and I've seen it argued out by some pretty smart guys. Hornadies manual will tell you deeper seating equals less pressure. Berger bullets ballastician says the opposite. And...you'd think there must be a right and wrong answer.
I've come to believe from reading the arguments that it has alot to do with the throat of the particular rifle. If it has a short throat seating shorter reduces pressure and heres why I think its so. It give the bullet a run up to the rifling allowing it to get through faster and ever so slightly further down the barrel making the combustion chamber ever so slightly bigger.
Now...on a long throat the opposite happens. With the long throat the bullet is ALWAYS going to build enough speed to get through the rifling transition quickly. So ..if you seat shorter in a long throat the bullet starts shorter and by the time max pressure is reached is less far down the barrel making the combustion chamber smaller than if you hung it out of the case further.
Its simply (in my feeble mind) what gets you through that rifling transition faster and further down the barrel before max pressure is reached.

 

[steve4102]

So, if you look at that 2nd graph, that's how I had always understood things....there's a valley in the pressure. Once you go short enough, the pressure climbs again as the bullet eats into case capacity.

Note that the pressure does not start to rise until the bullet is seated extremely deep, over a Quarter of an inch off the lands. I have no rifles that can be seated that deep. YMMV.

Back to the original question. As case capacity is reduced so is pressure until the bullet is seated well past normal conditions. I doubt any of Nosler's test rounds had bullets seated .250+ off the lands.

Now that that is out of the way and we know that under normal conditions reducing case capacity does not raise pressure.

Why does Nosler include this information in their manuals. For what purpose? Also, how would the average handloader go about verifying/testing grains of H20 under a seated bullet? Especially if the case full measurement is left out and cannot be use as a comparison?

 

[tddeangelo]

Since my posts seem to have cluttered your thread and not answered your question, I removed them. My apologies.

 

[woods]

I'm with you Steve, makes no sense

It would introduce more variables, i.e. seating depth difference from manual, bullet shapes, etc.

But it didn't make much sense to me for Nosler to team with Remington to change 30 years of 280AI chambering either

 

[Ridgerunner665]

But it didn't make much sense to me for Nosler to team with Remington to change 30 years of 280AI chambering either

I'm not convinced that they did...after much research...I'm thinking the confusion started 30 years ago, with different smiths chambering in different ways (set back barrel vs. not)...

In other words...Nosler didn't cause the confusion...but standardizing the round brought it to a head so to speak.

There are lots of people that didn't have any problems whatsoever with Noslers brass in the "old" chambers...

Just saying...


On topic....that 2nd pic Steve posted sums it up nicely...too short raises peak pressure, too long raises peak pressure, sweet spot in the middle...and it varies by powder burn rate and capacity of the case as to how much the pressure swings.

 

[Ridgerunner665]

Also...I've wondered the same thing about the case capacities in the load data...

Overflow capacity would be more useful to us.

 

[Oldtrader3]

If you are using a system based on calculating pressure which is similar to the Powley Computer to calculate load and chamber pressure, that system uses the H2O capacity with the bullet seated in the case. Perhaps that is why Nosler uses that capacity?

 

[Dwh7271]

Sorry to resurrect this but I knew I had read of the method Nosler uses and I found it with an explanation.
It's referenced in "Precision Shooting Reloading Guide" edited by Dave Brennan.pages 273 and 274. Comes originally from the 85% solution as a good starting point for the average rifle. I.e. A powder charge starting at 85% of a cartridges water capacity (with bullet) is a basic reloading principle. He broadens this out w further explanation as to powder efficiency, velocity etc.
Since these guys do/did Precision Rifle mag I figure they probably know what they're doing.
I'm sure a math whiz could take a full water measurement, compare it to Noslers number and work a percentage calculation to find that starting point. (I'm lazy, I let the computer figure it :grin: )
Anyhow, there's one point of reference on the water capacity with bullet.
FWIW.


OT3,
Sorry. Just reread your post. They referenced the Powley in a preface to the explanation I posted. Well said sir.

 

[Oldtrader3]

Thanks Dewey.