Author Topic: Ever Wonder Why Heavier Pellets in a PCP Tend to be More Efficient?  (Read 646 times)

rsterne

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Heavier pellets will generally produce slightly higher efficiency, particularly if you don't change the hammer spring preload.... They end up going slower, but the valve dwell is still the same, so the valve closes before the pellet has moved as far down the barrel.... That leaves more length for the air to expand, so more of the energy in it gets extracted, and the residual muzzle pressure is lower, resulting in less report.... In addition, slightly less air is released from the valve, because the length of barrel filled while the valve is open is less.... Since the heavier pellet often has higher FPE as well, from that extra energy extracted from slightly less air, the efficiency increases.... This makes the gun quieter, with more FPE, with the heavier pellets.... and often gains you a shot or two as well....

Bob


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Shorty

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Re: Ever Wonder Why Heavier Pellets in a PCP Tend to be More Efficient?
« Reply #1 on: September 20, 2017, 02:27:02 PM »
Never really thought about it but makes sense.

So (forgetting about accuracy), would a choked area at the breech achieve the same results?
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bnowlin

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Re: Ever Wonder Why Heavier Pellets in a PCP Tend to be More Efficient?
« Reply #2 on: September 20, 2017, 05:14:52 PM »
Bob would it be less likely to wobble so to speak.  And slightly more accurate.
Bobn

rsterne

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Re: Ever Wonder Why Heavier Pellets in a PCP Tend to be More Efficient?
« Reply #3 on: September 20, 2017, 05:45:28 PM »
Tim, why would a choked area at the breech make any difference to velocity/FPE, efficiency, or report?.... You lost me completely, I see no connection.... ???

Bob
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Shorty

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Re: Ever Wonder Why Heavier Pellets in a PCP Tend to be More Efficient?
« Reply #4 on: September 20, 2017, 05:58:12 PM »
Like a "cork" pop gun. Tight at first building up full pressure before moving. Just like the heavier slug.
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rsterne

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Re: Ever Wonder Why Heavier Pellets in a PCP Tend to be More Efficient?
« Reply #5 on: September 20, 2017, 06:17:42 PM »
Except in a cork "pop" gun the cork is at the end of the barrel.... and it is the pressure buildup behind it that launches it at all.... PCPs already have 2000-3000 psi available at the instant the valve opens.... Virtually that entire pressure is present at the base of the pellet/bullet before it has moved even 1 mm.... Any restriction in the barrel just increases friction, IMO.... At 3000 psi in a .22 cal the force available to accelerate the pellet is 114 lbs, and the drag is only a few lbs.... Most of the force goes into acceleration, and how rapidly that occurs depends on the mass (weight) of the pellet....

Bob
« Last Edit: September 20, 2017, 06:19:55 PM by rsterne »
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The Dumb Ox

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Re: Ever Wonder Why Heavier Pellets in a PCP Tend to be More Efficient?
« Reply #6 on: September 21, 2017, 02:55:32 AM »
Does the same hold true for CO2 rifles?

rsterne

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Re: Ever Wonder Why Heavier Pellets in a PCP Tend to be More Efficient?
« Reply #7 on: September 21, 2017, 08:19:15 AM »
Basically, yes.... and also for pumpers.... Pretty much any "pneumatic" airgun will follow the same trend.... There are a few exceptions, if you tune a gun for low power with a light pellet and then use a heavy one, the velocity may be so low that the power and efficiency may drop.... Springers (inc. Gas Ram) are totally different, because they work on a Adiabtic cycle which heats the air.... and the air used for the shot is the swept volume of the compression chamber.... Most Springers have an optimum weight range where the FPE, and hence the efficiency, will peak....

Bob
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