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 Post subject: Pressure/Velocity relationship with Nice Shot
PostPosted: Thu Dec 30, 2010 9:47 pm 
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Does the increased chamber pressure (relative to an equivalent lead load) when using Nice Shot translate into higher muzzle velocities?

I ask because the formula I'm looking at using for 20 gauge shows a pressure of 9,500 psi and a velocity of 1100 fps and was wondering if the increased pressure from using Nice Shot in place of lead would get me closer to 1200 fps. I don't need specifics, just a general idea. I would expect an increase in velocity but I may be missing something conceptually.

Thanks



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 Post subject: Re: Pressure/Velocity relationship with Nice Shot
PostPosted: Fri Dec 31, 2010 11:04 am 
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Muzzle velocity is not directly linked to pressure, regardless of shot material or payload.

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 Post subject: Re: Pressure/Velocity relationship with Nice Shot
PostPosted: Fri Dec 31, 2010 12:09 pm 
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RandyWakeman wrote:
Muzzle velocity is not directly linked to pressure, regardless of shot material or payload.


Yet without the pressure of the expanding gas generated by powder burning, there would be nothing coming out of the barrel, so there is "a" relationship direct or otherwise. Can you refer me to a more edifying discussion so that I might understand the nuances?

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 Post subject: Re: Pressure/Velocity relationship with Nice Shot
PostPosted: Fri Dec 31, 2010 12:30 pm 
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An exercise in futility is my position. If there was a calculatable relationship we wouldn't have Powder X providing 1100 fps at 9500 and powder Y providing 1200 fps at 8500 psi. The max absolute pressure has no useful relationship. It's how that pressure works throughout the firing sequence.

Of the top of my head, 100fps is a lot to make up while still being in spec.

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 Post subject: Re: Pressure/Velocity relationship with Nice Shot
PostPosted: Fri Dec 31, 2010 12:35 pm 
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There is an increase in velocity but not more than 20-40FPS. The pressure increase is caused by Nice Shot being slightly harder than magnum lead shot. When the gun is fired Nice Shot itself doesn't absorb much of the acceleration forces like softer lead shot does and presses outward to the sides of the hull until it gains momentum. This takes place a split second in the cartridge.

"This is comparing identical loads of Nice Shot to lead with same components."

This is why we've been working with Precision Reloading to get the reloading data for you good people.
Hope I explained it well.

Dan

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 Post subject: Re: Pressure/Velocity relationship with Nice Shot
PostPosted: Fri Dec 31, 2010 1:18 pm 
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Chukarshooter wrote:
RandyWakeman wrote:
Muzzle velocity is not directly linked to pressure, regardless of shot material or payload.


Yet without the pressure of the expanding gas generated by powder burning, there would be nothing coming out of the barrel, so there is "a" relationship direct or otherwise. Can you refer me to a more edifying discussion so that I might understand the nuances?



The approximate pressure cited by reloading manuals is only approximate, loosely approximate, and based on lab data in a "standard" test barrel. That pressure is not a pressure curve, it is only MAP-- maximum average peak pressure. Peak pressure is just a node that happens inside the shotshell. A pressure number does not define the entire pressure curve, yet it is the entire pressure curve that affects velocity. For a more through discussion see Lyman's or Hatcher's notebook.

A lower MAP value actually may yield higher muzzle velocity, you can see that in any reloading manual. While that may be counter intuitive, the basic flaw in thinking that "pressure" means anything specific is that chamber pressure and the pressure curve are two totally different things.

It would make more sense if shotguns had only chambers, not complete barrels, but they don't. The "pressure" is only from the chamber-- which is why it has no great meaning.

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 Post subject: Re: Pressure/Velocity relationship with Nice Shot
PostPosted: Fri Dec 31, 2010 3:41 pm 
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Thanks for the thoughtful explanations gentlemen.

I think I get it. Muzzle velocity is related more to the area under a velocity curve (duration of acceleration) and max pressure may occur only briefly as a crest or even a spike and the 1500 psi that Nice Shot may add is short lived thus adding negligibly to velocity. I'm guessing that with harder shot materials, such as steel, there is an even greater spike due to the lack of shot deformation. It's amazing to me that such a small thing can add so much pressure.

I was just hoping for a speed bonus to offset the need to download with Nice Shot.....can't have your cake and eat it too I guess.

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 Post subject: Re: Pressure/Velocity relationship with Nice Shot
PostPosted: Fri Dec 31, 2010 8:09 pm 
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There likely is a speed bonus, but not for the reason stated.

Nice Shot uses standard lead recipes. Though recipes are by weight, not by volume, if you are using a charge bar the payloads will drop light. You'll still have the same number of pellets, as the volume is the same, they will still fill up the case nicely and give you good-looking crimps.

But, what we have is (roughly) a 7% reduction in payload weight which may mean far MORE than a 7% MAP reduction and a velocity increase on top of that. Are you with me on this? Using 1-1/4 oz. charge bars will net you somewhere around 1.17 oz. payloads rather than 1.25. High antimony lead drops light, anyway.

You can check it on your own reloading press, but using a 1-1/4 oz. hunting lead load on a MEC 9000G often drops at 1.22 oz., is going to hit 1.16 oz. or so with Nice Shot. Rather than any MAP increase, you may well get a slight pressure reduction vs. lead and higher velocities on top of that (using MEC lead volumetric charge bars, the way they work from the factory).

Sounds like I need to call in a few favors from DRW, etc., to get the hard numbers.

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 Post subject: Re: Pressure/Velocity relationship with Nice Shot
PostPosted: Fri Dec 31, 2010 8:51 pm 
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RandyWakeman wrote:
There likely is a speed bonus, but not for the reason stated.

Nice Shot uses standard lead recipes. Though recipes are by weight, not by volume, if you are using a charge bar the payloads will drop light. You'll still have the same number of pellets, as the volume is the same, they will still fill up the case nicely and give you good-looking crimps.

But, what we have is (roughly) a 7% reduction in payload weight which may mean far MORE than a 7% MAP reduction and a velocity increase on top of that. Are you with me on this? Using 1-1/4 oz. charge bars will net you somewhere around 1.17 oz. payloads rather than 1.25. High antimony lead drops light, anyway.

You can check it on your own reloading press, but using a 1-1/4 oz. hunting lead load on a MEC 9000G often drops at 1.22 oz., is going to hit 1.16 oz. or so with Nice Shot. Rather than any MAP increase, you may well get a slight pressure reduction vs. lead and higher velocities on top of that (using MEC lead volumetric charge bars, the way they work from the factory).

Sounds like I need to call in a few favors from DRW, etc., to get the hard numbers.


Another bonus would be getting 42 to 43 7/8 oz 20 gauge loads per kilo rather than 40.

It will be interesting to see what Dan has to say about your 7% solution. I assume the test loads which showed 1500 psi higher pressures were loaded by weight not by volume.

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Beretta Silver Pigeon 12 and 28
Beretta Urika 2 12 gauge
Remington 870 Express 12 and Wingmaster 410
Weatherby Orion (SKB) 20 gauge


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 Post subject: Re: Pressure/Velocity relationship with Nice Shot
PostPosted: Sat Jan 01, 2011 9:58 am 
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Chukarshooter wrote:
Another bonus would be getting 42 to 43 7/8 oz 20 gauge loads per kilo rather than 40.

It will be interesting to see what Dan has to say about your 7% solution. I assume the test loads which showed 1500 psi higher pressures were loaded by weight not by volume.


Gentlemen, I believe were are taking this a little too analytically. The 1500PSI increase doesn't stay constant because of burn rates and payload size. But it was the maximum experienced so far in testing.

My factory 20 gauge ammo is 1 ounce of Nice Shot @ 1250-1300 FPS with an average of 9800 PSI.

Quite a few of the bulk shot buyers have been loading 3/4 and 7/8 ounce loads and love them too.

Best advice call Precision Reloading, a good quantity of the gauges and loads have been tested and are going to be printed, they will be more than happy to assist you with your data. "Last time I chatted with them, I told them what I had for components and they already had a load for that combo on the books."

Safety first brings a lot of good hunting!
Dan

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 Post subject: Re: Pressure/Velocity relationship with Nice Shot
PostPosted: Sat Jan 01, 2011 10:10 am 
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Loads data is always by weight and that won't change-- even though soft #9-1/2 lead and higher antimony #4 lead never have dropped the same. People drill out their charge bars, some send then to MEC to have them opened up, and there are adjustable charge bars as well.

Pressures are never exact and they are never even numbers. A published pressure is just a guide that comports to a standard-- it won't be the same in your gun under your ambient conditions. Primers vary by lot, so do wads, so do hulls. so does powder.



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