0.177 vs 0.22 energy efficiency

[AVS Stephen]

You're original question was about FPE, since you mention velocity of the the same weight pellet of different calibers. There has been a lot of discussion  about the air behind the pellet. But what about the air in front of the pellet? Unless you are shooting at something right in front of the barrel you must take into account the effeciency of the projectile with a smaller surface area and the same weight t(and same velocity) raveling through the air for a 100 yards. Two projectiles with same weight but different surface areas will reach terminal velocity differently. The thinner more torpedo like projectile should retain higher velocity at farther distances.

I do not have any scientific results but my .22 galatian shooting a 25 grain pellet at 860fps seems to have less arc than the same .25 pellet in 25 grains traveling at the same 860fps out to 109 yards.

I hope I'm not going off from the original discussion but it's something I often think about.

[Wolverineshooter]

You guys are all amazing! Thanks Rob, Matt, Dillon, Ribbonstone, Bob, Gary, Peter, Michael Stephne.
I found the following article that I think addresses the problem. In terms of my argument for a faster “speed of air” for small bore (which really should be higher pressure in a small bore due to smaller volume), the article showed that it is not enough to overcome the larger force due to big contact surface with the air. Here is the link: http://www.kiledjian.elac.org/phys%20001/Ballistics%20of%20Air%20Gun.pdf.

From this article I can conclude:
1.   For the same gun, you will have the same muzzle energy regardless of the pellet weight, as long as the friction between the pellet and the barrel are the same.
__ This is counter-intuitive to me, I thought the heavier pellet would have a little advantage. I would imagine the heavier pellet would have a higher friction, so based on this article, will have even less muzzle energy than a lighter pellet.
2.   Bigger bore will yield more muzzle energy provided the guns are the same except the bore size.
___It is not clear to me if a bigger pellet will have more friction or less friction. I would bet on the more side.
3.   Bigger bore requires longer barrel to achieve optimal muzzle energy
4.   When barrel length are optimized, in guns with very low friction, the big bore will have more muzzle energy. When friction is above certain threshold the smaller bore will have more muzzle energy.

So whatever the gun you have, make sure the barrel has minimal friction (really straight and uniform, no burs), and your pellets are symmetric, uniform in skirt and really smooth to minimize the friction! Many people use moly on their bullets for lubrication to minimize friction, that should help.

5. The time the pellet travel in the barrel is very shot (on the scale of <1/300 seconds scale), any air released after that time is a waste. So for PCPs we should have maximum openings in the air holes but use a weaker spring to keep the volume of the air up but shortening the time to maximize efficiency

[Wolverineshooter]

You're original question was about FPE, since you mention velocity of the the same weight pellet of different calibers. There has been a lot of discussion  about the air behind the pellet. But what about the air in front of the pellet? Unless you are shooting at something right in front of the barrel you must take into account the effeciency of the projectile with a smaller surface area and the same weight t(and same velocity) raveling through the air for a 100 yards. Two projectiles with same weight but different surface areas will reach terminal velocity differently. The thinner more torpedo like projectile should retain higher velocity at farther distances.

I do not have any scientific results but my .22 galatian shooting a 25 grain pellet at 860fps seems to have less arc than the same .25 pellet in 25 grains traveling at the same 860fps out to 109 yards.

I hope I'm not going off from the original discussion but it's something I often think about.

Your question is discussed in another thread: https://www.gatewaytoairguns.org/GTA/index.php?topic=132886.msg1320722#msg1320722

[anti-squirrel]

I'll just throw a general idea out there that I try to live by.  I've found that if I can get good-to-great accuracy at the distances I'm intending to shoot with a heavier pellet in a given caliber, that is what I stick with. 

A good example is the H&N Sniper Magnums in .177- 15.1 grains.  These pellets seem to do better as power levels increase, but even when I adjust for shot count in my PP700 (shooting ~ 550 FPS) they group extremely well.  I have taken several squirrel at lower velocities with these specifically because at the shorter ranges I'm using them (< 20 yards for pesting generally) I can put them wherever I want with precision- meaning into the ear from side shots or eye from frontal shots.  Crow Magnums are not as accurate across all my airguns, but their weight also merits exploring for those who prefer heavier-weight pellets... and heavier pellets in general maintain their energy levels in a given caliber.

Or to summarize, I like the heaviest pellet that afford good accuracy.  A small loss in velocity is worth it if I can maintain more precision, especially as distances increase.  But this also requires more bench-time learning not just the gun but the way the pellet behaves. 

Disclaimer: My choice is also influenced by my fast accumulation of Choice Hotel points converted to Amazon gift cards and thus getting H&N pellets "for free".   I generally avoid ordering over pellets on Amazon, but H&N arrive in perfect condition thanks to a somewhat sturdier tin with a screen-on lid.

[Wolverineshooter]

Peter, agree with you.

Within the caliber, heavier pellet tend to have better BC, and heavier weight makes them more stable (resistance to wind for example), so it will fly more true and deliver more bang. Of course the drawback is the shot will curve more and could be difficult for long distance shot.

Between caliber, things are a little different. larger caliber will have more muzzle energy to start with (assuming same gun except different barrel). But smaller bore pellets of the same weight will have better BC and preserve more energy, which could make the smaller bore a better choice for the longer range.

[rsterne]

Unfortunately, there is a lot of guesswork and opinion in this thread, that is taking it in a direction different to what actually happens.... In PRACTICAL terms, larger calibers shoot heavier pellets, and in fact the SD of "normal" or similar pellets INCREASES in proportion to caliber, and therefore so does their ability to carry energy downrange, or to buck the wind.... So, although there are obvious limits (you can't put a .50 cal barrel on a .177 pistol and expect reasonable performance).... generally speaking, in one given gun, the larger of two calibers will have more hitting power (FPE), and less wind drift.... but the smaller caliber will have a flatter trajectory and greater penetration....

Bob

[Wolverineshooter]

This is kind complicated, especially in terms of resistance and stability. So some actual experiment would be helpful.

[rsterne]

Test conducted with a modified 2250, comparing a .25 cal barrel and 25.4 gr. pellets (SD = 0.058) to a .30 cal barrel and 44.8 gr. pellets (SD = 0.071).... Both barrels were 25" long, and the power source was a single 12 gr. CO2 cartridge.... The same port sizes and valve volume were used for both tests, the ONLY change was the caliber and pellet.... Note that if you scale the 25.4 gr. JSB up to .30 cal, it would have a weight of 43.9 gr.... so the relative SD of the 44.8 gr. pellet shows a nearly perfect correlation to the expected SD increase being proportional to caliber.... ie the pellets are nearly identical in shape, and hence FF.... This will give the advantage in BC to the larger caliber, in just about exactly the ratio of (.30 / .25) = 1.2, as would be expected.... I used a BC of 0.039 for the .25 cal and 0.047 for the .30 cal in the calculations, although the BC of the 44.8 gr. JSB Exact .30 cal is actually a bit higher than that....

.25 cal.... 23 shots above 300 fps

594
600
593
585
571
559
560
553
547
540
542
533
539
529
526
518
514
519
509
492
452
408
360

Average velocity 528 fps.... Average energy 15.9 FPE.... Total energy per cartridge 366 FPE.... Efficiency in .25 cal is 0.88 FPE/CI....

.30 cal.... 20 shots above 300 fps

468
468
469
462
467
464
461
466
458
463
467
466
464
462
460
458
442
408
369
327

Average velocity 446 fps.... Average energy 20.1 FPE.... Total energy per cartridge 403 FPE.... Efficiency in .30 cal is 0.97 FPE/CI....

Since the SD of the .30 cal pellet is higher than the .25 cal, and the shape is nearly identical (both are JSB Exact).... the .30 cal pellet is not only starting with a 26% advantage in FPE, it will lose less velocity and energy as it goes downrange.... At 50 yards, the .25 cal pellet will have about 11.6 FPE remaining, while the .30 cal will have about 15.3 FPE.... an advantage of 32% at the target in favour of the larger caliber....

This is just one example of what happens in the real world, using typical pellets for the caliber, and the same gun, same power source, same barrel length, just a different caliber, shooting a normal pellet.... I hope that helps convey my point....

Bob

[Rob M]

excellent demo bob , I enjoyed looking through the numbers !