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#161 ·
I just spent 45 minutes reading through this entire thread and I've decided to simplify things by spending a few bucks on pressure testing some loads with Cheddite primers and go from there. After finally running through my win 209's, I'm forced to dive into my sunstantial Cheddite "break glass in case of emergency" supply. My Guerinis and Brownings and Winchester 42 all pierce those primers so I guess I'll just stock up on firing pins as well to keep on shooting. However in deference to the spirit of the original post, it's sad that Allegiant, Hogden and other powder manufacturers can't supply load data for Cheddite, knowing that's what many of their customers now have to work with. I would like to believe that since ourselves and our fathers and grandfathers have been their customers for decades, coupled with the fact that our sport and passion (and their non-government business) is holding on by a thread, that might inspire them to spend a few bucks and publish some SAFE data for their long time customers. We are all forced to wing it with the primers we are able to get out hands on these days and I for one would truly appreciate some help from them, if nothing else for the sake of providing us with some SAFE data to load their powder with.
 
#162 ·
dogchaser37 said:
I will ask one more time.

If what you say is true Nebs, that it is all about the shape of the base, then why does the Remington SP shell with a tall, flat basewad develop higher pressures using the same components than other flat basewad hulls, such as Federal Gold Medal, Cheddite, RIO etc? In this case the only real difference is the height of the basewad. Which of course means that the Rem SP hull has less volume than the others.

BTW, it is easy enough to find that what I am saying is true. Just look on the Alliant website under the steel shot data. All three lengths of Remington hulls are there and so are the facts, not opinions.

If the Alliant data isn't enough, look at the data in the Lyman 5th......same outcome.

And if that isn't enough I have some older data from when I developed data for those Remington SP hulls.
Click to expand...
The only Remington "SP" hull I can find data for is 3". I'm not going to engage in a data chase. Neither Hodgdon nor Alliant have reloading data for the Rem "SP" hull.
 
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#163 ·
Nebs said:
My understanding is the powder is all burned up before the wad starts moving up the tube of the hull. The wad and the payload take up all the space above the powder so that volume above the top of the powder is all taken up.

In the straight walled hull, the configuration of the powder with the wad on top is a short, fat cylinder. In the tapered walled hull, the configuration of the powder with the wad on top is more in the nature of cone with the pointed end loped off, or a taller, skinnier cylinder. GoldensAlways and I are of the view it is this shape difference that accounts for the undeniable fact it takes more powder in a straight walled hull to get the same performance obtained from a tapered walled hull.

It also is true the straight walled hulls have more internal volume than the tapered walled hulls.

Given these two differences, which one accounts for the difference in performance between the two hulls and why?

If it's the volume difference, how come the ballisticians have not found a way to maximize the effect by reducing the internal volume even further, reducing the amount of powder needed and increasing the performance. How does one account for the fact in both the tapered walled and straight walled loads, all the volume above the powder is taken up by the wad and the shot.

The shape difference seems to have influenced the people at Winchester because when they switched from the compression formed, tapered AACF hull to the otherwise straight walled AAHS, they saw fit to add the separate internal base-wad that mimics the effect of the tapered walled hull. To me, this is evidence they favored the shape of the powder charge over the volume of the hull.

We still are left with the "why." I have not had a chance to see if Hatcher discusses this in his Notebook, but I doubt it because I don't think tapered walled hulls were around in his time frame. I will see if an engineer I know can give me any help with it.
Click to expand...
There is no "why" in the business world to every question you raise...economics. Since you both believe there is less volume in some hulls, Boyle's Law should explain what you are having uncertainty about. Sure there are other less significant factors such as shape, wad friction, higher pressures usually providing more efficient powder burn and so on. But if you take time to do some basic algebra, you will see that Boyle's Law accounts for the vast majority of the variation confirmed by pressure testing.

Image

P_{1}
=first pressure
P_{2}
=second pressure
V_{1}
=first volume
V_{2}
=second volume
 
#164 · (Edited)
Nebs said:
My understanding is the powder is all burned up before the wad starts moving up the tube of the hull. The wad and the payload take up all the space above the powder so that volume above the top of the powder is all taken up.
Click to expand...
No, the wad moves/crush zone collapses prior to peak pressure. This is also why "slow" powders such as longshot are able to launch heavier/faster loads without going over SAMMI - the rate of wad movement and corresponding increase in the size of combustion chamber is enough to compensate for the extra gas/ongoing combustion. Same with Steel powder accounting for the different volume of shot and lack of set-back.

Image
 
#165 · (Edited)
Goldens Always said:
And the size of that chamber is the same. Only its shape differs. Why is this so hard to figure out?
Click to expand...
The size is not the same no matter how much you desire it to be. You are confusing the early partial expansion of the powder chambers with the max volume of the chambers that, once reached, begins rapidly spiking the pressure. All else being equal, CF AA hulls hit their smaller max volume earlier than other hulls because they have less volume and also generate higher pressure for the same reason...smaller max volume.
 
#166 ·
GrandLakeHunter said:
Here are hull volumes measured in grains of steel shot and grains of water. By no coincidence, they almost perfectly correlate to the psi variations commonly seen in different hulls. Not sure these numbers will convince Doubting Tom since many have noted the general principle and he has rejected it multiple times. I suggest that Doubting Tom google the contact info of any shotshell ballistics lab and listen to their professional response.

View attachment 42682
Chart provided by: Dave in AZ, 12 ga 2.75″ Hull Volumes, 2019
Click to expand...
The seduction of confusing correlation for causation will never cease.
 
#167 · (Edited)
Nebs and other naysayers, speaking about 12 gauge only, a Remington SP hull is a reifenhauser style hull, medium to high metal head, yellow, green or black plastic basewad, ribbed outer tube and made in 2 3/4", 3" and 3 1/2" lengths. They are used for most of Remington's hunting loads including the non toxic loads. The one pictured has the black basewad that is slightly proud of the primer. The hull walls are slightly thicker than most other straight wall hulls, which measured .028" on this hull compared to most other straight wall hulls that measure from .025" to .023" thick. They also are available in the other gauges. Remington denotes them as SP, other sources might say all plastic hull with a plastic basewad.

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Alliant clearly lists them as 2 3/4" Rem Nitro Mag, 3" Rem Nitro Steel and 3 1/2" Rem Plastic SP.

Would you like me to read the data for you? Or as adults do you think you can manage?

There is a whole bunch of reloading and components that consist of a lot more than target loads.

Here's my proof that volume of a shotshell affects pressure more than shape of the inner hull. Where is your proof?
 
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#168 ·
GrandLakeHunter said:
The size is not the same no matter how much you desire it to be. You are confusing the early partial expansion of the powder chambers with the max volume of the chambers that, once reached, begins rapidly spiking the pressure. All else being equal, CF AA hulls hit their smaller max volume earlier than other hulls because they have less volume and also generate higher pressure for the same reason...smaller max volume.
Click to expand...
Work that out with arithmetic.

We agreed above that prior to ignition, the "combustion chambers" are the same if the powder charges are the same and the wads are seated on the powder. Simply opening a hull shows that is the case.

note that almost all of the taper in a winchester case is above the wad cup. Cut a hull open and look - as I did the other day and posted on another thread.
Image


Look at the thickness of that hull wall. How much taper is there? Measure it. Will that amount of taper result in sufficient reductions in volume to satisfy Boyle's law? Again, P1/P2 has to equal V2/V1. You have P1 and P2, so now measure V2 and V1.
The taper is pretty minimal and most of it is below the wad cup, where we know, indisputably, the volumes are the same in both hull types.

That pretty much leaves us with shape, not volume being the cause.
 
#169 · (Edited)
1. At the end of the day your argument is invalid and comes down to.... things are the same because the volume of powder is the same and the different components look similar at T=0 (prior to ignition).

2. At T>0, prior to completion of combusion, there will be movement of the wad and corresponding expansion of the chamber. This occurs prior to max pressure and once it happens you are dealing with different volumes in the two cases.

3. You are not comparing apples to apples - only way you can make your argument work is by changing components between the shells. You have shown a tapered wad in a tapered hull but if you were to do the same with a straightwall the differences would be obvious - even more so trying to jam a straightwall wad into a tapered case.

4. If your argument is correct then changing wads should not affect pressure given that the area below the powder cup remains the same.... yet
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EXAMPLE #1
Image

Image



EXAMPLE #2
Image
 
#172 · (Edited)
AHI said:
So the 3 grans more powder doesn't mean any thing? The increase of 100fps doesn't mean any thing.?
Click to expand...
Did not mean to confuse and editied above post to clarify. There are two separate wad sub examples shown above... Duster vs. RXP at 22grains and Versatile vs. RedPC at 25 grains - everything else identical. Same FPS but note the pressure differentials.
 
#173 ·
500 psi is variation in test equipment.
1200 psi is showing an actual pressure increase.

Now I could be wrong but the Versalite wad is intended for sw hulls. They are a tight fit in a AA Tapered hull. At least the ones I have used were.
 
#174 · (Edited)
All quick pulls from the Alliant website. Only willing to put so much time into digging stuff up. Once again, same components except for the wad sub - 1500psi difference. Given that at T=0 the charges have equal volume, the only way to account for the pressure differential is the variance in combustion chamber volume as the different wads move/compress.

Image

Image

Image
 
#176 ·
Nebs said:
My understanding is the powder is all burned up before the wad starts moving up the tube of the hull.
Click to expand...
That is incorrect. Have you ever seen a shot fired at night under the lights and notice flame shooting out the end of the barrel? I have, many times.

That is slow powder burning as it exits the barrel. Have you ever noticed barrel residue after firing a shell? A lot of that is unburned powder.

There's no way for a powder charge to completely burn before the wad starts moving up the barrel.

The gasses created by the burning powder and the laws of physics prevent that from ever happening.
 
#178 ·
The shape of the combustion chamber does matter. Engine engineers also use the shape of the chamber to modify the burn in a gas or Diesel engines. If the shape doesn’t matter then a shaped charge wouldn’t work for explosives. Boil’s law is based on ideal conditions. There are no ideal conditions in real life engineering. We experiment to find the closest practical use. Actual practical testing validates theory not the other way around
 
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#179 · (Edited)
dutch7373 said:
The shape of the combustion chamber does matter. Engine engineers also use the shape of the chamber to modify the burn in a gas or Diesel engines. If the shape doesn’t matter then a shaped charge wouldn’t work for explosives. Boil’s law is based on ideal conditions. There are no ideal conditions in real life engineering. We experiment to find the closest practical use. Actual practical testing validates theory not the other way around
Click to expand...
This is why I used the above recipes as examples... identical volume/taper/shape of the combustion chamber at T=0. The wads difference in movement/change in combustion chamber volume from T>0 accounts for the variance in Max PSI between the recipes.
 
#180 · (Edited)
dutch7373,

Yes it does matter, with diesel and gas engines, because you are trying to increase the efficiency for getting all the exhaust out and getting the fresh fuel and air charge in. They are also using exhaust headers, turbo chargers, correct length intake manifolds, super chargers and electronics, depending on application, to get the most out of the fuel/air charge for torque, horsepower and economy. In that case you are definitely concerned with combustion chamber design and shape.

I am sure that primer placement and depth into the powder charge does make a difference and I think if you go back in my texts you will see that I never said that hull design doesn't make a difference. However this is a solid propellant, that is being supplied some of it's oxygen by the primer and you are only trying to extract the heat and expanding gas from the burning powder. You are not concerned with scavenging the exhuast gases and bringing in a fresh charge of fuel and air, with a piston flopping up and down. Two completely different applications.
 
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