Also read original post over, if by scratch you mean prediction, I already covered why this cannot be done so simply. -yes, exactly thats why it was strange for me and wasnt be able to figure out. Like this its clear.
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Tuning Larger calibers seem much more efficient?
- Thread starter EPG
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Its because you need information on the pcp, variables...state of tune, plenum pressure and volume, caliber, barrel length, they all matter too much to give anything less than a wide range that is less than acceptable to give any real proximity.
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Stock configuration my airgun used maybe 3-4 cc's per shot but ony did 40-50 fpe.....now it does 62 fpe @ 5.2 cc's per shot.
You simply can't extrapolate that either because a pcp with different variables will do wildly different shot volumes, port size alone greatly effects efficiency depending on power level.
For a given pcp, as power goes up fpe per cc generally goes down (efficiency).
-Matt
You simply can't extrapolate that either because a pcp with different variables will do wildly different shot volumes, port size alone greatly effects efficiency depending on power level.
For a given pcp, as power goes up fpe per cc generally goes down (efficiency).
-Matt
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I know its not possible ... its pretty obvious, thats why i was asking cause i would be pretty surprised if you would have a formula for that 
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You tell me the following variables I will give you an approximate air usage likely within 95% accuracy provided theres no hammer bounce skewing the air usage.
Caliber
Barrel length
Plenum Volume
Port Size
Set point (or if unregulated average pressure / mid fill range)
Volume between valve seat and pellet
Axial or non-axial flow
Pellet weight
Energy output
Your altitude
Your Temperature
Not so simple...and I do have a formula for that.
Caliber
Barrel length
Plenum Volume
Port Size
Set point (or if unregulated average pressure / mid fill range)
Volume between valve seat and pellet
Axial or non-axial flow
Pellet weight
Energy output
Your altitude
Your Temperature
Not so simple...and I do have a formula for that.
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The most I'd narrow it down, for an average pcp its about 30% of the bore's volume +/- 5%.... simplest formula and generalization that applies to the majority of pcp's in a decent state of tune. Not too large of a gap either.
-Matt
-Matt
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Wow, 86 posts and counting. In less than a week.
I like it.
Very educational.
Internal ballistics is definitely an area that I have invested very little efforts so far.
One ballistics field at a time, first external ballistics, than terminal, I can't do it all at the same time....
➠ So, after seeing there are several people on this thread knowing about 100 times more than I do about this, may I ask an efficiency of caliber question for a particular scenario?
➠ The soon to be released Huben GK1 pistol:
Barrel = 8.3" (21.0cm)
Non-regulated
Air tube = 85cc (let's say max. 300bar, though it can go up to 350))
● In .22cal, it can do, reportedly, 45 shots with 23FPE (with 16gr pellets at 804fps) — which I suspect will have a fairly large MV variation (unregulated!) — likely too much for my taste.
● In .25cal, we have been given an actual shot string with only small MV variations: from 300 to 150bar, 18 shots, at 38FPE (34gr pellet at 720fps).
Of course, the extremely heavy pellet (34gr) for such a short barrel (8.3") — results in rather optimistic muzzle energies — a 25.4gr pellet would be much more realistic.
Here are my questions:
(1) Air efficiency: If I understand the discussion thus far — for the same amount of air used from the tiny 85cc tube, for the same amount of shots until the unregulated MV drops below acceptable limits — I get more muzzle energy with a larger caliber? (Properly tuned)
(2) Loudness: Would the .25cal at 42FPE (25.4gr, 860fps) be a lot louder than the .22cal at 31FPE (19gr, 860fps)?
(3) Muzzle velocity: Would it be easier to tune the .22cal to shoot 19 grain pellets at 900fps than the .25cal to shoot 25 grain pellets at the same velocity, 900fps?
➔ Of course, I understand that we are hypothesizing, and there is no guarantee in any of this — but these are the practical questions* that I have been martering my brain with — and your expertise can shed some light on possible answers or at least principles that will help me.
Thank you!
Matthias
*I have similar questions about whether to get a compact .30cal (500mm barrel), or a full size .30cal (600mm)....
RTI Prophet II with a balanced valve:
I want 45 grainers to exit with an MV of 900 or 950 — but at the same time I want this gun to shot quietly — no big bore big boom.
(4) I know the 600mm barrel will be quieter, but do I need it? Or can I get away with the 500mm?
(Because, I really like compact bullpups!)
I like it.
Very educational.
Internal ballistics is definitely an area that I have invested very little efforts so far.
One ballistics field at a time, first external ballistics, than terminal, I can't do it all at the same time....
➠ So, after seeing there are several people on this thread knowing about 100 times more than I do about this, may I ask an efficiency of caliber question for a particular scenario?
➠ The soon to be released Huben GK1 pistol:
Barrel = 8.3" (21.0cm)
Non-regulated
Air tube = 85cc (let's say max. 300bar, though it can go up to 350))
● In .22cal, it can do, reportedly, 45 shots with 23FPE (with 16gr pellets at 804fps) — which I suspect will have a fairly large MV variation (unregulated!) — likely too much for my taste.
● In .25cal, we have been given an actual shot string with only small MV variations: from 300 to 150bar, 18 shots, at 38FPE (34gr pellet at 720fps).
Of course, the extremely heavy pellet (34gr) for such a short barrel (8.3") — results in rather optimistic muzzle energies — a 25.4gr pellet would be much more realistic.
Here are my questions:
(1) Air efficiency: If I understand the discussion thus far — for the same amount of air used from the tiny 85cc tube, for the same amount of shots until the unregulated MV drops below acceptable limits — I get more muzzle energy with a larger caliber? (Properly tuned) (2) Loudness: Would the .25cal at 42FPE (25.4gr, 860fps) be a lot louder than the .22cal at 31FPE (19gr, 860fps)? (3) Muzzle velocity: Would it be easier to tune the .22cal to shoot 19 grain pellets at 900fps than the .25cal to shoot 25 grain pellets at the same velocity, 900fps?➔ Of course, I understand that we are hypothesizing, and there is no guarantee in any of this — but these are the practical questions* that I have been martering my brain with — and your expertise can shed some light on possible answers or at least principles that will help me.
Thank you!
Matthias
*I have similar questions about whether to get a compact .30cal (500mm barrel), or a full size .30cal (600mm)....
RTI Prophet II with a balanced valve:
I want 45 grainers to exit with an MV of 900 or 950 — but at the same time I want this gun to shot quietly — no big bore big boom.
(4) I know the 600mm barrel will be quieter, but do I need it? Or can I get away with the 500mm? (Because, I really like compact bullpups!)
Upvote 0
Wow, 86 posts and counting. In less than a week.
I like it.
Very educational.
Internal ballistics is definitely an area that I have invested very little efforts so far.
One ballistics field at a time, first external ballistics, than terminal, I can't do it all at the same time....
➠ So, after seeing there are several people on this thread knowing about 100 times more than I do about this, may I ask an efficiency of caliber question for a particular scenario?
➠ The soon to be released Huben GK1 pistol:
Barrel = 8.3" (21.0cm)
Non-regulated
Air tube = 85cc (let's say max. 300bar, though it can go up to 350))
● In .22cal, it can do, reportedly, 45 shots with 23FPE (with 16gr pellets at 804fps) — which I suspect will have a fairly large MV variation (unregulated!) — likely too much for my taste.
● In .25cal, we have been given an actual shot string with only small MV variations: from 300 to 150bar, 18 shots, at 38FPE (34gr pellet at 720fps).
Of course, the extremely heavy pellet (34gr) for such a short barrel (8.3") — results in rather optimistic muzzle energies — a 25.4gr pellet would be much more realistic.
Here are my questions:
➔ Of course, I understand that we are hypothesizing, and there is no guarantee in any of this — but these are the practical questions* that I have been martering my brain with — and your expertise can shed some light on possible answers or at least principles that will help me.
Thank you!
Matthias
*I have similar questions about whether to get a compact .30cal (500mm barrel), or a full size .30cal (600mm)....
RTI Prophet II with a balanced valve:
I want 45 grainers to exit with an MV of 900 or 950 — but at the same time I want this gun to shot quietly — no big bore big boom.
(Because, I really like compact bullpups!)
1) If you mean per shot yes, if you mean total fpe combined across the pressure range then that depends on state of tune.
2) Yes, but the 25 cal detuned to 31 fpe should be quieter than the .22 cal at 31 fpe.
3) Neither are easy out of 8.3" barrel and should be about equal difficulty.
4) 500mm barrel in 30 cal shooting 45 gr will need 170+ bar for 950 fps, or 150+ bar for 900 fps assuming 85% bore porting (rough estimate) and around 70cc of plenum based on their website . The muzzle blast will be fine if you tune it well. However with the 600mm barrel you would need only 150 bar for 950 fps and 125~ bar for 900 fps.
Both will make noise, 100mm extra barrel won't suddenly quiet down an airgun making 80FPE. So, you can go either way, a balanced valve can handle either 120 bar or 170 bar no problem when designed well. Their regulator says 180 bar max so seems fine.
-Matt
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