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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sun Aug 02, 2020 12:20 pm 
Crown Grade

Joined: Thu Aug 31, 2006 10:06 am
Posts: 3656
Location: UK, England, Britain
Some of these consepts i used to develop that nontox assay i did. I also added an energy deplete shell. I got 2200ftlb energy available from 26grain of powder. At 80% burn, the shells are brilliant.




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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sun Aug 02, 2020 4:38 pm 
Shotgun Expert
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Location: Plainfield, IL
I've done a lot of work over the years with .50 cal muzzleloaders. 209 ignition, straight wall application-- fairly simple. (NOT A SHOTGUN LOAD).

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The following is a 90% propellant burn.

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Going to 60 gr., the propellant burn is about 93%.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sun Aug 02, 2020 5:21 pm 
Tournament Grade

Joined: Tue May 26, 2020 10:12 am
Posts: 102
Location: Iowa
Man you got that right. I've been lost for all of this page and most of the 1st :lol:


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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sun Aug 02, 2020 5:38 pm 
Tournament Grade

Joined: Tue May 26, 2020 10:12 am
Posts: 102
Location: Iowa
RandyWakeman wrote:
john54 wrote:
I think I have a handle on this


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


I've been lost for about two and a half pages. :lol:


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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sun Aug 02, 2020 7:12 pm 
Presentation Grade

Joined: Wed Nov 19, 2008 3:04 pm
Posts: 815
Location: Eastern Ohio
The whole idea here is to have enough gas from the powder to siphon off at the ports to operate the action. Faster powders tend to completely burn before the crimp actually opens and sometimes there is not enough gas at the ports to completely cycle the action. Slower burning powders tend to use more powder to get to the same velocity therefore more gas is available at the gas ports. The law of conservation of mass says that if you burn 20 grains of powder you will get 20 grains of gas and ash. The more powder the more gas and ash. Smokeless powder is fairly efficient especially under pressure therefore more powder more gas. More gas the action works.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Sun Aug 02, 2020 9:38 pm 
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RandyWakeman wrote:
I've done a lot of work over the years with .50 cal muzzleloaders. 209 ignition, straight wall application-- fairly simple. (NOT A SHOTGUN LOAD).

Image

The following is a 90% propellant burn.

Image

Going to 60 gr., the propellant burn is about 93%.

Image
How this is relevant to the OP's question, I can't say. But what I would like to know, and what the post doesn't say, is how is the burn percentage was determined. The relevance of the graphs????

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Mon Aug 03, 2020 12:20 am 
Crown Grade

Joined: Sun Mar 03, 2013 11:01 am
Posts: 6038
Location: Newton Kansas
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.

Boyles Gas Law works perfectly well with ALL firearms, whether or not they are self-loaders driven by gas or not.

Yes it is "inexact" because there is a certain amount of heat of the gas lost to the barrel steel, you go ahead and calculate that loss for me, in the milliseconds that firing ammunition takes, that pressure loss due to cooling is, IMO, not very important. It is MINOR compared to the rest of the physics.

Go ahead and start with the exact combustion temperature of the propellant gasses, which may vary 500*F or so depending on exactly which powder is used.

I am also ignoring the cooling effect of simply gas expansion, separate from loss through the conductivity of the barrel, the simple act of the projectile moving an inch and dropping pressure from 11,000psi to 5,500psi, cools the gas, and shrinks it's volume, slightly. Again, this effect is MINOR IMO compared to the rest of what is going on at the same time.

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 Post subject: Re: pressure and cycling semi auto
PostPosted: Mon Aug 03, 2020 12:45 am 
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OldStufferA5#1911 wrote:
Boyles Gas Law works perfectly well with ALL firearms, whether or not they are self-loaders driven by gas or not.


Absolutely not. NASA can help: https://www.grc.nasa.gov/www/k-12/airplane/boyle.html .

Boyle's law only works with an ideal gas, "ideal gas" refers to a hypothetical gas composed of molecules which follow a few rules: Ideal gas molecules do not attract or repel each other. The only interaction between ideal gas molecules would be an elastic collision upon impact with each other or an elastic collision with the walls of the container.

If you have a hypothetical firearm, I suppose you can use the ideal gas. Boyle's law assumes a constant temperature-- firearm applications are anything but constant temperature. https://journals.physiology.org/doi/ful ... .87.4.1543

Quote:
Of course, pressure × volume is constant only if temperature is constant. Boyle was aware of this, although he did not pursue it. In the text near the table shown in Fig. 1, he described how he heated the trapped air in the small limb of the U tube with the flame of a candle “so that we scarce doubted, but that the expansion of the air would, notwithstanding the weight that opprest it, have been made conspicuous, if the fear of unseasonably breaking the glass had not kept us from increasing the heat” (3).

Finally, we need not go into the issue of to what extent Boyle’s work was based on the work of others and, indeed, whether Boyle’s name should even be attached to the law. This has been discussed extensively elsewhere (5, 9, 10). Suffice it to say that at least five other people have some claim to be considered, including Viscount Brouncker, Robert Hooke, Edmé Mariotte, Henry Power, and Richard Towneley. In fact, in France the law is known as “la loi de Mariotte.”


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Quote:
Shotgun load pressures will vary more than expected due to differences in crimp strength, powder column height and shot weight variations. This is then manifest in velocity deviations that affect the lead required to hit targets.

These traces were taken from an SKB 12 G double with the strain gage glued over engraving, then calibrated to a known pressure load . Due to the unusual shape around the chamber on "doubles", accurate peak pressure in PSI can only be measured by calibrating the system to a known pressure load.

The third shot used an old hull. Note the reduced pressure due to weaker crimp.


If Robert Boyle were alive today, he would say, "Clean your shotgun!" as he died in 1691, he was unaware of nitrocellulose propellants or even cartridges. A primer change alone can change peak pressure by 5000 psi. Boyle's law is fail-boat as far as shotguns.

Pressure curves in shotshells are not linear.



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