Tuning Larger calibers seem much more efficient?

Jump to latest Follow Reply
explorer said:
First of all ... i was starting to re-read the efficiency thread on the beginning and im stuck at one thing.
47/72 = 35% gain in energy (and thermal efficiency) -how the heck you got this number? The increas from 47 to 72 is increase of around 53 percent.
It would be a 35 percent in case of drop. I hope your other calculations are with correct percentage calculations :)
If a 'dry shot' over drives a valve to the point the hammer bounces off the rear of the valve, it will shut faster. -it can be ...
Awesome Matt, thanks for confirming that my 35% was a reasonable amount of energy to gain! -yeah actually it was 53
Not only is the Prophet Performance V1 the easiest airgun to adjust (reg pressure & hammer spring preload) … its also the easiest rifle to NOT have to adjust, lol.
-need to deeply agree as a prophet 2 owner ... damn that rifle shoots extremely well even without tune not like an FX what without tune shoots 6 MOA groups :ROFLMAO:
What is sonic choking? I googled for it but probably you dont mean this one ....
View attachment 378024
Click to expand...

If he works in reverse (taking the .30 cal down to .22 cal) he drops 35% in power...(47/72 = 35% reduction where as 72/47 = 53% increase), that is the way I approached the calculation. You can figure out how to formulate the other way if you desire, its not difficult to re-arrange. So the 35%/53% decrease/increase is expected. If I said he increased 35% earlier I misspoke, if I said theres a 35% difference than I did not, either way, really not my area of interest to formulate so I cobbled something together that made sense when I tested through a range of calibers.


Sonic choking, lol...funny! Here is a good read. For smaller diameter ports they will choke a lot easier with dry fires than air guns ported near full bore, certainly with larger bores, likewise will higher temps, and higher pressures.

Take note of 'Flow Pattern'

Choked flow - Wikipedia

en.wikipedia.org en.wikipedia.org
 
Last edited:
Upvote 0
Stubbers said:
SD1 = 3.14159*(SmallerBoreDiameter/2)^2
SD2 = 3.14159*(LargerBoreDiameter/2)^2

SD1 = .03812
SD2 = .07068

PD =(1-(SD1/SD2))*100-(√((1-(SD1/SD2))*100)*1.5)

PD (Power Difference expressed in FPE) = 36%


Not sure how this scales, with different barrel lengths, or even different calibers/states of tunes, but if you keep pellet ratio in excess of this result or just your sd1/sd2 difference, you should end up somewhere close using the above formula
Click to expand...
Yes, but the power increas as told was 53 percent because we was talking about increase/gain so the formula above also probably not legit for calculation of power increase. Agree?
 
Upvote 0
explorer said:
Yes, but the power increas as told was 53 percent because we was talking about increase/gain so the formula above also probably not legit for calculation of power increase. Agree?
Click to expand...

You have to reverse the percentage, you know they work both way correct? Maybe not? Any percent calculator online can do this for you. The % increase is not equal to the % decrease, its not mirrored. You can use the above most simple approach I just mentioned...its too good to be true.

.3/.22 = 36% (36% original equation)
.25./.22 = 13% (15% original equation))
.25/.177 = 41% (40% original equation)

However my original equation is better...you just have to know how to extrapolate it. *edit* it works nearly the same lol....
 
Last edited:
Upvote 0
Stubbers said:
You know whats funny, if you take the diameter itself and not surface area, you get 36% increase....coincidence?

.3/.22 = 36%
.25./22 = 13%

Maybe it is just that simple?
Click to expand...
Honestly? I really think its a coincidence, as the diameter INCREASE is 36 percent and power increase 53.
Dont really think the drop of one have something common with the increase of the other one. I mean for me logically its not okay, if you know what i mean.
 
Upvote 0
Stubbers said:
You have to reverse the percentage, you know they work both way correct? Maybe not? Any percent calculator online can do this for you. The % increase is not equal to the % decrease, its not mirrored. You can use the above most simple approach I just mentioned...its too good to be true.

.3/.22 = 36%
.25./.22 = 13%
.25/.177 = 41%

However my original equation is better...you just have to know how to use it.
Click to expand...
Ofc i know. Thats the case that you comparing the increase and drop what i think we should not but compare increase with increase and drop with drop.
 
Upvote 0
Here is another percent...the total difference in energy

47 to 72 is...

42% total difference. (disregarding the increase or decrease, just total change)

So using that 42% change between 47 and 72....and the SD difference....59%....that leaves 17% unanswered for.

You can say, well maybe its the SD difference (59%) that contributes to the 53% increase (47 to 72) with the same coefficient of loss, but that is a bit of cheating using whole % change and a % increase....

Where as my original equation is looking at the decrease from the calibers and calculating the decrease, but to look at the increase you'd need an entirely different formula or to extrapolate using mine...and to that, good luck.

Add to that there is no way friction and pressure loss behind the projectile contributes to 17% in the above. Of course this whole equation and approach to getting even ball park is easier said than done, my simplest reduction approach doesn't even look right when I compare .177 to .25, but its better than nothing..using surface diameter alone certainly isn't going to be exact. You need to know how the pressure gradient behind the pellet works (average pressure, this changes with plenum volumes and shot volumes...), as well as that particular pellets fitment into the bore and friction down the bore.

Without knowing someones plenum volume, pressure, tune state (efficiency), there is no way to be 100% accurate.

The reason I came up with around 36% reduction from .3 to .22 was because in my internal ballistic spreadsheet I was able to approximate the average pressure down the bore in each caliber given a nominal plenum / pressure / barrel length.

-Matt
 
Last edited:
Upvote 0
Here is what various calibers look like taking to the max (plateau) using same barrel length, but increased pellet weights...its not perfect but this follows what OP saw from his .22 to .3, while tuned differently/lower...

42/72 = 35% decrease or 53% increase...

My chart predicts... (at 2100 psi, 100 cc plenum, 20" barrel)
56/101 = 45% decrease or 80% increase... (this is plateau, full bore on each with enough pellet weight to obtain reasonable fpe)

Extrapolate all you want, this is about as real as it gets, but the formula is not easy...and much less easy for predicting below a plateau...


1691182662657.png
 
Last edited:
Upvote 0
Here I manipulated my chart data to show what OP saw (notice .22 to .30), to do that, there could be several explainations...

Port size for example, is all I used, If I go down to .25" porting on the .30" cal opposed to full bore porting that alone drops the FPE to 72~, so if the porting is not equal % to that of the bore in each caliber, that alone could explain away a portion of your power differential between calibers...as that would not be 'all things equal', likewise would apply to the pellet weight maintaining sectional density, or plenum volume maintaining the same average pressure during the shot cycle for a 47 fpe shot as it would a 70+ fpe shot...let alone a 200+.

1691183569086.png


-Matt
 
Last edited:
Upvote 0
So I think in summary, the reason why OP only saw 53% gain instead of the 85% increase in Surface Diameter from .30 cal to .22, and well technically its..

.218 vs .308 no?

Which is a 100% percent increase and 50% decrease, ( my above charts does use .22 and .3 rounded)

Spreadsheet predicts 48 decrease / 93 increase at plateau when I use .218 and .308, surface diameter alone predicts 50 decrease / 100 increase. Seems pretty spot on to use SD to ballparking then...for plateau.

Here is .218 vs .308

1691193099641.png


And back to the summary, being either state of tune, plenum, the ports % of bore diameter favoring .22 cal, or a combination thereof.

Why does my spreadsheet fall short of 100% increase when surface diameter increases 100%, and only predict 92.7% increase? My spread sheet calculates the average pressure loss as I have expressed through-out this thread. Larger bores have a steeper pressure gradient than smaller bores.

-Matt
 
Last edited:
Upvote 0
I showed a small change (only with .22 vs .3) earlier on my graph with port size favoring .22 cal, what about if we change plenum volumes around? Easy peasey..you'll notice the lower calibers are MUCH less affected than the larger calibers...as expected. Hence one of the few reasons you cannot use barrel volume alone, nor should one omit plenum volume (or pressure drop behind pellet, or pellet weight differential, or port% of bore differential) as the plenum volume skews the entire calculation in favor of smaller bores,

200cc plenum, full bore 20" barrel 2150 psi
1691196477467.png


40cc plenum full bore 20" barrel 2150 psi
1691196526696.png
 
Last edited:
Upvote 0
Likewise, longer barrels even effect this, taking the barrel to 32"...

You'll notice the increase went from 90% @ 20" barrel down to 87.5% with the 32...and the decrease goes from 47% to 46%.

1691199110210.png


Barrel down to 10"


1691199168370.png



93% increase and 48% decrease.

This beautifully demonstrates, the longer you go in barrel, the less gains the larger bores get, and this even leaves out a good chunk of loss...

-Matt
 
Upvote 0
explorer said:
One thing which is unclear for me, how do you calculate the ammount of used air? I mean, okay we have got the plenum size and pressure but how by what formula you calculate the ammount of air passing through the valve?
Click to expand...

As a prediction, you would need to know the guns data just as prediction for power difference between calibers would, at least for precision.

For a gun you have the data on its relatively simple.

If you can calculate how many psi you use per shot, you can extrapolate that to volume.


For Psi Per Shot:

Regulator pressure drop....(PsiStart-PsiFinish)/ShotCount*(ReservoirVolume/PlenumVolume))

Reservoir pressure drop... (Psistart-PsiFinish)/ShotCount


To determine the CC's ejected (volume) instead of PSI (pressure), you take the PSI use you currently calculated..

For unregulated...(PsiStart*ReservoirVolume/(PsiStart-PsiUsedPerShot)) - ReservoirVolume

For regulated...(Setpoint*PlenumVolume/(Setpoint-PsiUsed)) - PlenumVolume


-Matt
 
Last edited:
Upvote 0
Stubbers said:
As a prediction, you would need to know the guns data just as prediction for power difference between calibers would, at least for precision.

For a gun you have the data on its relatively simple.

If you can calculate how many psi you use per shot, you can extrapolate that to volume.


For Psi Per Shot:

Regulator pressure drop....(PsiStart-PsiFinish)/ShotCount*(ReservoirVolume/PlenumVolume))

Reservoir pressure drop... (Psistart-PsiFinish)/ShotCount


To determine the CC's ejected (volume) instead of PSI (pressure), you take the PSI use you currently calculated..

For unregulated...(PsiStart*ReservoirVolume/(PsiStart-PsiUsedPerShot)) - ReservoirVolume

For regulated...(Setpoint*PlenumVolume/(Setpoint-PsiUsed)) - PlenumVolume


-Matt
Click to expand...
Ah okay so just counted by actual air consumption, i tought you have some general formula to calculate it from scratch :D
 
Upvote 0
explorer said:
Ah okay so just counted by actual air consumption, i tought you have some general formula to calculate it from scratch :D
Click to expand...

Define "from scratch"? Maybe share the formula you had in mind?

A well tuned pcp uses about 20% of its bore volume per shot, and a poorly tuned pcp uses about 50% of its bore volume...and anywhere in between depending on the airgun, not all airguns are the same, unless you think they are?

That means depending on my tune, my 19.5" .25 cal could be using between 3's cc's or 8 cc's of air, depending on state of tune and some other factors. Not too precise without ALL the gun data huh?

Thermally you generally get 15-35% efficiency from a pcp, this ALSO depends on your state of tune, which..is no different than the above calculation suggesting anywhere between 4 and 8 cc's for my 19.5" .25 cal...unless I de-tune it to 12-20 fpe, then perhaps it will only use 2 cc's.



-Matt
 
Last edited:
Upvote 0
explorer said:
Ah okay so just counted by actual air consumption, i tought you have some general formula to calculate it from scratch :D
Click to expand...

Stubbers said:
As a prediction, you would need to know the guns data just as prediction for power difference between calibers would, at least for precision.
Click to expand...

Also read original post over, if by scratch you mean prediction, I already covered why this cannot be done so simply.
 
Upvote 0
You must log in or register to reply here.
Top Bottom
Back
Home
Forums
Resources
Menu