Question on PCP shot count - .177 vs. .22

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ctshooter

ctshooter

Member
Oct 30, 2018
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CT, United States
I have to admit I am a bit confused. There's a lot of rifles out there where I look at the specs and the gun seems to get more shots in .22 caliber compared with the shot count in .177 caliber. And in general the fpe is much higher in the .22 version. How is this possible? Does it have something to do with the bore size of the .177 being less efficient than a larger bore? If so - does that mean that there is an ideal caliber for best PCP efficiency? It seems that .22 or .25 appear to get the best shot count, with .25 being on the declining end and .30 sucking down a lot more air to move the heavier projectile.
 
In the rifles I own that are available in multi caliber configurations the rule that seems to apply is the smaller the caliber the faster the pellet travels and since the smaller pellet requires less air to be propelled you will get more shots per fill with a .177 vs a 22.

below is from Edgun west site.

177 -- EDgun Heavy 10.44 grains -- 950 f/sec

.22 -- EDgun Heavy 18.1 grains 920 f/sec

.25 -- EDgun King 25.4 grains m/sec 920 f/sec



Number of shots per fill (220-120 bar) with the recommended pellet and

speed:



.177 -- 60

.22 -- 50

,25 -- 40
 
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Efficiency is not force x area. Efficiency is measured thermally or volumetrically, but not with surface area or force...efficiency is based on energy output with either model...each caliber respectively being able to hit the same efficiencies...just at different power levels...force X area can however calculate the energy obtainable, much as I do here to calculate a pcp's performance. The FPE/FPS predictions are simply force X area X distance...



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View attachment 1548808227_8361655505c50f023f2df57.21062466_PCP_Performance.ods




Given the same valve duration, a larger caliber/port will always flow more air because of how much mass of ejected air is able to fit into said space in said time...



Given the same energy level, the larger caliber (.25 for example) will generally have reduced valve duration requirements to hit 12 fpe than a smaller caliber (.177 for example)...thus being more efficient and capable of more shot count at equal energy levels to the smaller caliber. HTH



-Matt
 
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Given the same energy level, the larger caliber (.25 for example) will generally have reduced valve duration requirements to hit 12 fpe than a smaller caliber (.177 for example)...thus being more efficient and capable of more shot count at equal energy levels to the smaller caliber. HTH



-Matt
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Matt - thanks. That explanation does make sense if we are comparing equal power output.
 
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"Does it have something to do with the bore size of the .177 being less efficient than a larger bore?"

In a nutshell, yes.
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Incorrect, its not less efficient...efficiency is defined as...

"the ratio of the useful work performed by a machine or in a process to the total energy expended or heat taken in"



valve duration or pellet distance down the barrel relative to valve close time is what effects efficiency, not bore diameter...in fact, bore length has a greater effect on efficiency of air use than bore diameter, generally efficiency goes down with larger bores provided you're using that bore size to its potential...so you cannot simply imply 'smaller bore = less efficient'...that entirely depends on another set of variables, where its not a static truth or constant...
 
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To put in perspective, a 275 FPE .357 may be shooting in the neighborhood of 4500 MG of air, where as a .177 at 18 fpe may only be using 200 MG of air. The work that goes into the air pushing its OWN weight adversely effects efficiency, thus making the .357 that is operating at nominal levels less efficient than the .177 at its nominal level...there is just no work around to that, its physics. Couple that with more surface area in the bigger diameter bore for more thermal loses, a much larger throat / transfer plenum / port which equates to MORE thermal and kinetic energy losses, the small bore at its nominal power will be far more efficient than the big bore at its nominal power level. HTH



-Matt
 
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Okay perhaps we are misusing a commonly used term here, the basics of what I said regardless of correct terminology is very simple, with regard to shot count you require less air to propel a .22 pellet than a .177 pellet to achieve the same muzzle energy, in the UK for instance this is set at 12FPE.

So all other things remaining equal a .22 CAL 12FPE rifle with a 200CC cylinder for example will return more shots per fill than a .177 12FPE rifle with everything else remaining the same, this is absolutely proven.

It is not the same as stated above when referring to how much muzzle energy would be produced from to differing calibers or the useage of air.
 
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Matt, I knew someone would dispute my simple answer, and I'd have to respond with perspective.

The OP's questions relate specifically to .177 versus .22 PCP shot-counts and muzzle energies. That being the case, I stand by my simple answer. Yes; in PCPs of the power levels being marketed in both calibers, .22 caliber returns higher shot-counts, greater muzzle energies, or both, than identical .177 PCPs. 

I'm no rocket scientist or engineer, but I consider that more efficient. Certainly as regards a straightforward answer to the OP's straightforward question.
 
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If you are looking at a gun that is offered in 3 calibers and the .177 doesn’t have a much better “shot count” than the others, it’s probably because the manufacturer has a basic set tune designed around the .22. Then they just swap a .177 or .25 barrel and sell the gun. I view airguns the same way I view real guns. You can put a 130gr bullet in a .243 and max load it to try and have it be a .270 Winchester, but it will never be as efficient. Same goes for airguns. If you keep FPE out of the equation and use pellet weights appropriate with each caliber, a .177 will always have a higher shot count. If you try to pretend a .177 is a .22, or a .22 is a .25, efficiency can go right out the window.
 
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Hopefully this helps the OP with the original question ....

As a tuner ... lets take a look at what EACH caliber can do in the same gun where each had been tuned for that specific caliber. that calibers weight of pellet being shot at optimum speed of @ 880 fps.



REGULATED MARAUDER with light hammer and some valve tweaks etc ... 3k fill pressure. ( different Reg set pressure )

.177 caliber shooting a JSB 10.3 @ 880 fps +/- @90 shots inside an ES of 10 fps ( 3K to 1.6K )

.22 caliber shooting a JSB 18.1 @ 865 fps +/- @45 shots inside an ES of 10 fps ( 3k to 1.8K )



There you have some REAL WORLD data that proves with no doubt that looking at caliber and a pellet weight realistic to the caliber shot at near equal velocity in a gun tuned to not over dwell valve ... A .177 far out shot counts the larger caliber on the same amount of air used.
 
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Matt, I knew someone would dispute my simple answer, and I'd have to respond with perspective.

The OP's questions relate specifically to .177 versus .22 PCP shot-counts and muzzle energies. That being the case, I stand by my simple answer. Yes; in PCPs of the power levels being marketed in both calibers, .22 caliber returns higher shot-counts, greater muzzle energies, or both, than identical .177 PCPs. 

I'm no rocket scientist or engineer, but I consider that more efficient. Certainly as regards a straightforward answer to the OP's straightforward question.
Click to expand...

You're incorrect and Motorheads real world example lines up 100% with my theoretical example...the .177 is far more efficient...you're going down the wrong rabbit hole with your linee of thought and theres nothing wrong with that...I've done it plenty, but trust the tuner and my expertise when we say a .177 at its nominal power is far more efficient than a .22 at its nominal power...



You can't just reduce the power on one caliber and say oh its more efficient...I already stated that is the case, the point of the matter is at nominal levels, the smaller calibers are more efficient...if you wanna get a 30 cal that shoots 10 fpe just because its more efficient than a .177 at doing it, then I have to question your methods....


Why not reduce the power on BOTH calibers equally? Guess what, the smaller caliber still wins...you have to keep the power proportionate to the respective calibers or the test is not fair...so any reduction on the .22 you suggest would have to be followed up with the equal reduction in power on .177...
 
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The fly in your ointment Motorhead is your .22 example is approaching twice the power as your .177 example. Retest with the .22 dialed down to the same 17.7 foot-pounds as your .177 produces.... or if you prefer, with the .177 dialed up to 31.1 foot-pounds of the .22.
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I read the Q as ... Shot count

We're not talking about the area the air has to work against, or are we talking that with larger calibers you gain projectile weight.

I took it as EACH CALIBER running at equal speed with a weight of pellet being in the upper range of weight for said caliber. This makes the comparison show it merit without compromising normal operation of either.



Scott

Motorheads AG Tuning Services
 
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I think the ".22 getting more shots" term usually comes from UK where they are limited by max allowed muzzle energy, if not having a FAC gun. I would guess if you own a .22 gun and have no energy restrictions (like in US), most people would probably not adjust a .22 down enough in speed where it actually would gain more shots per fill than a .177.

So if you are buying a gun in UK the specs might say the .22 will have more shots (being a none FAC gun), but not in US.
 
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