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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 10:50 am 
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garrisonjoe wrote:
You two or three are talking past each other. The volume of the tank is constant. The AMOUNT of gas in the tank increases with pressure. When pumped into the tank, the volume of the gas is the same as the volume of the tank. You can't talk accurately about AMOUNT of a gas unless you talk the WEIGHT of the gas (or the moles of gas, more precisely, and what a chemist would do).

Using the term VOLUME of gas always requires you to consider the PRESSURE it is at. A volume of a gas is not an accurate way to specify the AMOUNT of gas, unless you also specify the temperature and pressure it is at. Gases are hard to measure because of that. Liquids like water or hydraulic fluid are easy to specify by volume, because those liquids do not change volume as pressure increases.

Now, most shotgun powders generate close to the same weight of gas from the same weight of powder. Some generate it faster (faster powders), some slower (amazingly, called slower powders). The magic rule of thumb that about 18 grains of powder will make enough gas in a 11 or 9/8 ounce load to work a gas semiauto comes from the fact that all the smokeless powders have nitrocellulose as the main component. It burns to make mostly carbon dioxide and steam (gases). The weight of nitrocellulose (close to the same in most powders) burns to make the same WEIGHT of gases for most powders, but at different speeds and peak pressures and port pressures depending upon the exact powder and the speed deterrent additives. And substituting nitroglycerin for some of the nitrocellulose (as double base powders do), boosts the amount of gas produced just a little bit, and adjusts the speed of the burn.

Quote:
More pressure means more volume.

Nope, more pressure means more amount of gas fits (has been generated) in the barrel space at the time of measurement.


good luck, garrisonjoe


Nice and clearly worded. Thank you.




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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 11:18 am 
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Denver1911 wrote:
RandyWakeman wrote:
Denver1911 wrote:
I have to ask:

How can different powders have different volumes of gas at the ports?


Quote:
For example, an AL sized cylinder is filled with nitrogen at 2000 psi. What is the gas volume of nitrogen from the cylinder?

P(1) is 2000 psi
V(1) is the internal volume of AL cylinder 29.5 liter*
P(2) is 14.7 psi
V(2) is the unknown volume of gas

Solving the equation above for V(2) gives:
V(2) = [p(1) x V(1)]/P(2) = (2000 psi x 29.5 liters)/14.7 psi = 4013 liters

(approximately 140 cu. ft.)


More pressure means more volume.


Uh .. no. Volume is a measure of .. volume. You can’t fit 4013 liter of gas inside of a 29.5 liter container .. if you put it in there, it becomes 29.5 liter of gas. Albeit at a different temperature and pressure. But once inside the container it is 29.5 liters.

Maybe you mean “volume at standard pressure?”


You can call it producing more volume after the ports if that helps you. That's where the work takes place, after the ports, which is a very long ways from being a tank. A barrel is hardly a tank, either: it is a rapidly expanding combustion chamber. The pressure behind the wad rapidly drops throughout its travel from muzzle to breech. What pressure it is at the ports, exactly, with any load is anyone's guess. You won't get that from any reloading manual.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 12:07 pm 
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john54 wrote:
I think I have a handle on this


john54 wrote:
I just got back from the Trap range and the nice and clean CZ-712 cycled the 1oz AA's 1180 fps. just fine. I was a little worried for a bit. I had set up for 1oz loads and had started thinking of the money I had wasted because it wouldn't cycle them. I did notice the difference in recoil between the 1oz and the 11/8 oz. Not much, but significant.


In your case, you've already discovered the "answer." All it was, was a dirty gun. We can all stare at reloading manuals for days, but that won't clean your gun.

There are so many variables involved that no shotgun manufacturer will tell you much of anything about the pseudo-mysteries of pressure. They mostly just suggest that you use a shell with sufficient power to cycle the action. While vague, it really has to be. Lube makes a difference, crud makes a difference, temperature makes a difference, tolerance stack-up makes a difference, and so it goes. Sometimes, the diameter of the gas ports themselves vary so much that a load will cycle with one barrel, but not with another barrel of the same chamber length and barrel length for the same gun. Interchangeable doesn't mean identical.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 12:19 pm 
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If you are having trouble with ammunition cycling a gas-operated autoloader, you might help solve it by using a heavier charge of a slower burning powder. It will produce a lower peak pressure (a metric that is irrelevant to solving the problem) but a larger amount of gas. More gas is what you need, not more peak pressure. All else being equal, more powder equals more gas.

Also, many times, you can help solve the problem by using a drill bit to auger the crud out of the gas ports.

But it sounds like the OP solved his problem with a good cleaning of the gun.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 12:36 pm 
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I have a couple of Beretta 303's that won't cycle reliably with anything less than 20 grains of powder. They don't care what the powder label says on the side on the side of the can. 20 grains or they become a complicated single shot.

For 2-3/4" loads, the 20 gauge will only cycle ammo loaded with Longshot or Lil Gun. A Federal hull + 20 grains of Longshot and it's reliable as a swiss watch. It eats 3" hunting ammo without a glitch. This gun was like new when I bought it. It appeared to be unfired and put in a safe until an estate sale was called for.

The matching but well used 12 gauge will not cycle standard Red Dot, Clays, or Extra Lite target loads. However, tip the Lyman scale past 20 grains of any powder and it'll cycle without issue.

It seems reasonable to me that a grain of powder produces a similar amount of gas to any other powder. Low pressure vs higher pressure load data doesn't seem to correlate to cycling reliability. In fact I'm currently burning through some Universal Clays in the 12 gauge that produce well below 8,000 psi.


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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 4:25 pm 
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Hal4son wrote:
It seems reasonable to me that a grain of powder produces a similar amount of gas to any other powder.


It doesn't. The nitroglycerin content of a propellant helps define the energy content. See https://projects.nfstc.org/firearms/mod ... t04_01.htm . While most, not all, shotshell propellants are double-based, not all have the same nitro content.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 4:39 pm 
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RandyWakeman wrote:
Hal4son wrote:
It seems reasonable to me that a grain of powder produces a similar amount of gas to any other powder.


It doesn't. The nitroglycerin content of a propellant helps define the energy content. See https://projects.nfstc.org/firearms/mod ... t04_01.htm . While most, not all, shotshell propellants are double-based, not all have the same nitro content.


16 grains of powder (no matter the type) produces 16 grains of combustion byproducts .. mostly gasses we hope. It’s physics. Are you saying that some powders produce more gas than others per grain? If this is the case, are the powders that produce less gas per grain dirtier because more of their original mass is left as non-gas?


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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 4:51 pm 
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Denver1911 wrote:
16 grains of powder (no matter the type) produces 16 grains of combustion byproducts .. mostly gasses we hope. It’s physics. Are you saying that some powders produce more gas than others per grain?


Of course. Blackpowder leaves about 50% of itself behind as solids.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 5:51 pm 
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Denver1911 wrote:
RandyWakeman wrote:
Hal4son wrote:
It seems reasonable to me that a grain of powder produces a similar amount of gas to any other powder.


It doesn't. The nitroglycerin content of a propellant helps define the energy content. See https://projects.nfstc.org/firearms/mod ... t04_01.htm . While most, not all, shotshell propellants are double-based, not all have the same nitro content.


16 grains of powder (no matter the type) produces 16 grains of combustion byproducts .. mostly gasses we hope. It’s physics. Are you saying that some powders produce more gas than others per grain? If this is the case, are the powders that produce less gas per grain dirtier because more of their original mass is left as non-gas?
It can't get any simpler than this. Despite what Randy might say with his red herring reference to black powder, if you test for the null hypothesis and assume zero residue is left after combustion, 100% of the powder gets converted to gas. The more grains of powder you put in the load, the more gas you will get. It makes no difference what type of powder you use. Burn rate makes no difference and density makes no difference, weight makes all the difference. It's called the conservation of mass principle. The mass of the powder equals the mass of the gas (assuming 100% combustion).

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 6:35 pm 
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Nebs wrote:
Despite what Randy might say with his red herring reference to black powder, if you test for the null hypothesis and assume zero residue is left after combustion, 100% of the powder gets converted to gas. The more grains of powder you put in the load, the more gas you will get. It makes no difference what type of powder you use. Burn rate makes no difference and density makes no difference, weight makes all the difference. It's called the conservation of mass principle. The mass of the powder equals the mass of the gas (assuming 100% combustion).


Why would anyone bother to assume 100% combustion? That's obviously not the case. The statement was "16 grains of powder (no matter the type)"-- the type clearly matters a great deal.

Not all nitrocellulose is created equal, nor are all propellants. Ping-pong balls are nitrocellulose: got any load data for them?

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 6:43 pm 
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RandyWakeman wrote:
Nebs wrote:
Despite what Randy might say with his red herring reference to black powder, if you test for the null hypothesis and assume zero residue is left after combustion, 100% of the powder gets converted to gas. The more grains of powder you put in the load, the more gas you will get. It makes no difference what type of powder you use. Burn rate makes no difference and density makes no difference, weight makes all the difference. It's called the conservation of mass principle. The mass of the powder equals the mass of the gas (assuming 100% combustion).


Why would anyone bother to assume 100% combustion? That's obviously not the case. The statement was "16 grains of powder (no matter the type)"-- the type clearly matters a great deal.

Not all nitrocellulose is created equal, nor are all propellants. Ping-pong balls are nitrocellulose: got any load data for them?


The statement was, “16 grains of powder (no matter the type) produces 16 grains OF COMBUSTION BY PRODUCTS.” .. a true statement. Type does not matter for this statement to be true. Oh, and “mostly gasses we hope.” Type certainly determines how much is as and how much is non-gas.


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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 6:44 pm 
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RandyWakeman wrote:
Hal4son wrote:
It seems reasonable to me that a grain of powder produces a similar amount of gas to any other powder.


It doesn't. The nitroglycerin content of a propellant helps define the energy content. See https://projects.nfstc.org/firearms/mod ... t04_01.htm . While most, not all, shotshell propellants are double-based, not all have the same nitro content.


How does that muddled point or the link provided add insight to this conversation? It's a point with no perspective, perameters or relevance.

Longshot is one of the high nitro content powders. However if you look at 20 gauge target loads, Longshot lists some of the heaviest powder charges. In fact, of all the powders listed on hodgdonreloading.com only SR4756 comes close to those powder drops maxing out at 20-21 grains for loadings around 8,000 psi. Longshot starts at 20 grains and runs up to 25 (Federal hull, 7/8 oz lead). With pressures starting at 8,000 and running up near 12k.

However if you look closer at those SR4756 and Longshot loadings, both produce about 8,000 psi with 20-21 grains of powder.


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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 6:48 pm 
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Hal4son wrote:
However if you look closer at those SR4756 and Longshot loadings, both produce about 8,000 psi with 20-21 grains of powder.


So what? Chamber pressure is not a pressure curve, nor is chamber pressure pressure at the gas ports themselves.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 6:51 pm 
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RandyWakeman wrote:
Hal4son wrote:
However if you look closer at those SR4756 and Longshot loadings, both produce about 8,000 psi with 20-21 grains of powder.


So what? Chamber pressure is not a pressure curve, nor is chamber pressure pressure at the gas ports themselves.


:roll:


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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 7:29 pm 
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RandyWakeman wrote:
Nebs wrote:
Despite what Randy might say with his red herring reference to black powder, if you test for the null hypothesis and assume zero residue is left after combustion, 100% of the powder gets converted to gas. The more grains of powder you put in the load, the more gas you will get. It makes no difference what type of powder you use. Burn rate makes no difference and density makes no difference, weight makes all the difference. It's called the conservation of mass principle. The mass of the powder equals the mass of the gas (assuming 100% combustion).


Why would anyone bother to assume 100% combustion? That's obviously not the case. The statement was "16 grains of powder (no matter the type)"-- the type clearly matters a great deal.

Not all nitrocellulose is created equal, nor are all propellants. Ping-pong balls are nitrocellulose: got any load data for them?
Because assuming 100% combustion assumes zero residue, the essence of "testing for the null hypothesis." So, it appears you have never heard of testing for null hypothesis. In this case, testing for the null hypothesis demonstrates that the weight of the powder equals the weight weight of the gas, and is an application of the conservation of mass principle. And, for purposes of application of the principle, all nitrocellulose and all propellants are equal. None can produce more mass on combustion than they had before combustion. Randy, do you realize how much fodder for cross-examination you leave behind with posts such as these?

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Last edited by Nebs on Sat Aug 01, 2020 7:34 pm, edited 1 time in total.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sat Aug 01, 2020 7:33 pm 
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RandyWakeman wrote:
Hal4son wrote:
However if you look closer at those SR4756 and Longshot loadings, both produce about 8,000 psi with 20-21 grains of powder.


So what? Chamber pressure is not a pressure curve, nor is chamber pressure pressure at the gas ports themselves.
YGBSM!

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sun Aug 02, 2020 12:12 am 
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Denver1911 wrote:
I have to ask:

How can different powders have different volumes of gas at the ports?

Volume of the cylinder is pi * r^2 * h. Pi is constant. r is half the barrels diameter. h is the distance from back to the hull to the ports. These don’t change by powder. The gas fills the allotted volume.

Do you mean mass?

The same amount (weight, mass) of powder, within a very small difference depending on exact composition of the powder, will produce the same volume of gas.

The thing is, powders burn at different rates, Blue Dot take a heck of alot longer to burn (in microseconds) than Red Dot does, so a given load that creates 11,000psi using a certain mass of Red Dot, say, 18 grains, WILL NOT produce the same pressure (11ksi) using Blue Dot.
It will produce the same gas volume, BUT, at these pressures, the BD is so slow that the hull can open and the payload can start moving, increasing the volume behind that wad's gas seal.
This is the reason that, to get the same PRESSURE, you have to burn much more of the slower powder.
More powder burned creates more gas.

More gas created in the larger space (because the wad moved), same pressure, but less pressure drop as the wad heads down barrel (Boyles Gas Law). This creates more Port Pressure.

Boyles Gas Law:
Any gas created inside a confined space (a cartridge and barrel), will create a certain pressure.
Every time you double the volume of that confined space, pressure drops by half.
{since the barrel diameter is unchanging, the "space" is defined by the base inside of the cartridge/hull (basewad) and the base of the projectile (wad gas seal). Every time the distance from the gas seal to the basewad doubles, pressure drops by half}

A fast burning powder (Red Dot) can all (18 grains) burn off before the hull even gets a chance to open, gas seal to basewad distance may be as short as 3/4" (powder thickness plus compressible cushion section of wad).
36gr of Blue Dot, to get the same pressure, the hull will manage to open and the wad slides fwd. 1/2", making a gas seal to basewad difference of perhaps 1-1/2".
Once the powder has burned off, Boyles Law takes over and pressure drops to 1/2-value every time the basewad to gas seal distance doubles.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sun Aug 02, 2020 8:58 am 
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OldStufferA5#1911 wrote:
(Boyles Gas Law)


The reason Boyle's law does not work with semi-auto shotguns is that it assumes a constant temperature and a closed system.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sun Aug 02, 2020 9:57 am 
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RandyWakeman wrote:
OldStufferA5#1911 wrote:
(Boyles Gas Law)


The reason Boyle's law does not work with semi-auto shotguns is that it assumes a constant temperature and a closed system.
Boyle's Law works perfectly well because you have a fixed mass of matter. If you assume volume and temperature are fixed and the only thing you change is the mass of the gas, a heavier powder charge will give you more pressure than a lighter powder charge. Boyle's law is not relevant to how fast you convert the solid to gas or how quickly you let it out of the container.

People tend to focus on the peak pressure figures in the data and assume higher peak pressure will have more gas than lower peak pressure. That assumption is false. What matters is the area under the curve, which represents the amount of gas, not where the peak of the curve occurs.

And what's different about gas operated autoloaders in this regard?

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sun Aug 02, 2020 10:00 am 
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john54 wrote:
I think I have a handle on this


Aren't you glad that you just cleaned your gun? :lol:



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