GTA
All Springer/NP/PCP Air Gun Discussion General => Air Gun Gate => Topic started by: DarkRattle on March 22, 2017, 02:28:14 PM
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See I've always been lost at this, what determines MORE penetration, ENERGY (Foot pounds) or Speed (Feet Per Second)? Say I have a .25 25grain JSB being thrown out at 910 FPS at a piece of wood, and let's say I have another pellet (34 grain JSB .25) thrown at the same piece of wood going slower (810 fps), which one will penetrate more? The one with more energy or the one with more speed? I know for instance if it were a .22 vs a .25 both same energy the .22 would out penetrate it because of the less surface area, but I'm comparing same caliber. Can someone give me a scientific(ish) answer ?
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Given the same diameter pellet, I'd say the one that expands the least.
Probably the heavier one in a hunting situation.
Maybe the faster one if shooting into wood?
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The bias IMO near always go's to the projectile with the least frontal area that by piercing a small hole first before increasing diameter to pass the rest ... or simply is smaller in diameter from the onset.
Weight and speed certainly part of the equation too.
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I've done some shooting with different pellets into both squirrel carcasses (mainly skulls) and Cornish hens. The biggest determinant for 2 pellets that weigh close to the same going at the same speed is the pellet shape. If you want to penetrate flesh, nothing beats a pointed pellet.
But there are a number of factors: what the pellets hits (bone? just meat/muscle?), the hardness of a pellet (Crosman domes and JSB domes may enter at the same speed, but Crosman will continue on through where a JSB deforms enough to shed all it's energy inside the skull), and the weight. Generally a heavier pellet with the same shape as a lighter pellet will continue further through "meat". The best scientific-ish answer is knowing the resistance to penetration and then using some fancy math. However, ballistic gel is what everybody seems to use, and in those cases, pellet shape plays a role big-time. A pointed Prometheus pellet weighing the same as a wadcutter will zip on through where the wadcutter stops pretty darn quick. It's what makes wadcutters such amazing pellets for small game hunting at shorter ranges. When dealing with your example- two pellets with the same approximate shape, but one far heavier than the other, I'd think the heavier one will out-penetrate the lighter one given the following:
A simple fact of energy is an object motion tends to stay in motion, and energy is related to mass. More mass at a given velocity means more energy, and it will want to stay in motion.
I'm not keen on wood or phonebooks for measuring penetration, as temperature and moisture content have an impact on both (less on a phonebook). And even shooting the same piece of wood in different areas can give different depths. The only "test" I like is shooting at a piece of meat. I'll also add I generally go only for headshots, so penetration is almost a non-issue since it only takes about 4 or 5 FPE to scramble a squirrel brain. All my airguns can do that at longer distances than I'm shooting. If shooting at birds, the vast majority are pretty fragile internally. I still try to go for headshots unless it's a HOSP, which just about any projectile will kill outright with a body-shot.
Having said all of this, I still try to use the heaviest pellet I can shoot accurately. More mass on the point of impact means more energy, and I'd rather the pellet not over-penetrate.
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My thought on the matter if the pellet shape is the same has the pellet with greater fpe penetrating more deeply. Why? It takes energy to penetrate. The pellet having the greater energy should penetrate more deeply.
This is assuming both pellets have the same frontal area and the same configuration. I'm also assuming neither is keyholing, which would present a greater frontal area and change the equation.
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http://www.gatewaytoairguns.org/GTA/index.php?topic=42959.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=42959.0)
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Sectional density for penetration.
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http://www.gatewaytoairguns.org/GTA/index.php?topic=42959.0 (http://www.gatewaytoairguns.org/GTA/index.php?topic=42959.0)
that is a very cool test. I wish the inches of penetration were given, so that you can compare between blocks a little better, but its still really cool.
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Penetration is proportional to the product of the Sectional Density and the Velocity.... SD = Wt. (gr.) /7000 / cal^2 (in.).... so it takes into account the bore area when you calculate it....
The actual penetration depends entirely on what you are penetrating, but for a given, consistent medium, with a given pellet, the penetration is proportional to the velocity.... If the velocity and caliber are constant, then the penetration is proportional to the weight.... If the velocity and weight are constant, then the penetration is inversely proportional to the square of the caliber (ie the bore area).... For a given caliber, the penetration is proportional to the Momentum (velocity x weight)....
Bob
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Doesn't the shape of the pellet head have a marked effect on penetration. It is far easier to drive a nail with a point on it than a nail with the point ground flat.
Admittedly the things being penetrated by a pellet are softer than wood but a sharp knife penetrates a hide easier than a blunt one. Not a good analogy unless you visualise stabbing rather than slicing.
Maybe I am missing something about sectional density. I thought that would be the ratio of pellet mass to frontal area of the pellet so the roundness or pointedness would not change that ratio.
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Yes, of course, as does the medium being penetrated.... but the OP asked which was important, energy or speed.... It is not just the shape of the point that matters, a roundball will outpenetrate a skirted (diabolo) pellet with a round nose, of the same weight, caliber, and speed....
Bob
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Yes that is a really nice study that Bob put together. To me, the most interesting takeaway is that domes penetrate equal to or better than pointed pellets. That was the one claim that would make pointed pellets worthwhile so need to waste my money on them any more. Sure, every once in a great while one will find a tin of pointed pellets that group decently at modest distances but it always seems to fall apart by 40 yards.
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I think Peter hit on an important variant, and that's the hardness of the projectile. Which also influences expansion.
With bullets, a copper alloy(mono) or a hardbal/fmj will almost always out penetrate a bullet of the same weight and diameter conventional cup and core hunting bullet with a hollow point or exposed lead tip traveling the same speed.
This is even true of an all copper bullet with a lower SD than it's C&C counterpart. Although most copper bullets are of a lower weight so they can be pushed to a higher speed to help initiate expansion.
And thinner jacketed varmint or target type bullets often have very little penetration at high speeds.
Thus, an alloy, or lead alloy pellet should penetrate more than a softer pure lead pellet.
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I think in wood they would penetrate the same. In flesh the heavier one would penetrate more.
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Right Resterne , I overlooked the original simple question and added a complication.
The other complications that have also been added just goes to show nothing is simple.
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Yep, and some things aren't obvious.... like round nose (hemispherical) pellet penetrating just as well as pointed ones.... Softer pellets penetrate less ONCE they start to expand, but unless they have a flat nose or hollowpoint, that doesn't really happen at airgun velocities.... and even then HPs differ widely in the velocity it takes to make them expand.... ONCE they expand, however, their penetration decreases rapidly, replaced by a wider wound channel....
Bob
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Yep, and some things aren't obvious.... like round nose (hemispherical) pellet penetrating just as well as pointed ones.... Softer pellets penetrate less ONCE they start to expand, but unless they have a flat nose or hollowpoint, that doesn't really happen at airgun velocities.... and even then HPs differ widely in the velocity it takes to make them expand.... ONCE they expand, however, their penetration decreases rapidly, replaced by a wider wound channel....
Bob
For penetration purposes, a hollow point that expands seems to basically quickly decrease sectional density.
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Too much speed can actually hinder penitration in some cases.
If the bullet/pellet dumps too much energy too fast it can over expand and not penitrate as far as one that is slower, or harder.
We do see this more on the powder burning side of things.
Also some cast bullets if pushed to fast can explode dumping all the energy in the first few inches and fail to penitrate deeply.
For max penitration the old buffalo guns were the example. Speed 1200 to 1400 fps with a large round ball or large for caliber bullet. They would go the long way through a buffalo and exit.
Back to airguns, slightly harder, heavier pellet would be my choice if penitration is what I am after. Pointed prefered, then domes, hollow points last, as again they will expand faster, reducing penitration.
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Again, once you start talking expansion, then the factors that effect penetration are changed.... The projectile is now larger, so the SD drops, and the penetration is decreased.... If it fragments, then each fragment has a lower SD.... A portion of the energy it had at impact goes into expanding the projectile, and is lost in heat and mechanical deformation, and that energy loss comes from the Kinetic Energy it had, which means the projectile has to lose velocity just from the expansion process, which again reduces the penetration.... These effects are outside the OPs question, but are still interesting in their own right, and can be explained by reversion to basic scientific principles....
You don't need to push hollowpoint bullets very fast to have them come apart violently.... Here is an example of a 51 gr. BBT in .25 cal in the mid 900s hitting a block of soap.... Hollowpoint on the top, FN solid on the bottom, same energy (about 100 FPE)....
(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/25%20cal%2051%20gr%20NOE%20BBTs_zpsazje5llc.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/25%20cal%2051%20gr%20NOE%20BBTs_zpsazje5llc.jpg.html)
The HP would cavity, opened up to show the damage and size of it....
(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/HP%20Cavity_zpscloonc0j.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/HP%20Cavity_zpscloonc0j.jpg.html)
The recovered bullets, FN on top, HP on the bottom....
(http://i378.photobucket.com/albums/oo221/rsterne/Ballistics/Side%20and%20Front_zpsejc5kmlc.jpg) (http://s378.photobucket.com/user/rsterne/media/Ballistics/Side%20and%20Front_zpsejc5kmlc.jpg.html)
In theory, they should have had the same penetration.... but only if they didn't expand.... As you can see, even the solid expanded significantly.... Had it been a much harder lead, or even a round nose instead of having a 70% Meplat, it may well have completely penetrated through that block of soap.... The one thing we haven't mentioned in this discussion is the VOLUME of the wound channel.... I think you will find that is closely related to the MOMENTUM of the bullet at impact, providing the bullet stays inside the target.... That is why a larger caliber bullet, of equal SD and velocity (and therefore equal penetration)... has more killing power.... the wound channel is larger in diameter (area).... Twice the caliber, four times the area, and volume.... and for equal SD, four times the weight and momentum, at equal velocity.... Conversely, for a given caliber, the penetration would be proportional to the weight times velocity, which is the momentum.... and since the hole should be the same diameter (area), then the volume would be proportional to the penetration, which would be proportional to the momentum....
Bob
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Using formulas (where ~ means "proportional to")....
Since Penetration ~ Velocity x Sectional Density
and.... Sectional Density = Weight (lbs.) / Caliber^2....
Penetration ~ Velocity x Weight / Caliber^2
Volume ~ Caliber^2 x Penetration
Therefore.... Volume ~ Caliber^2 x Velocity x Weight / Caliber^2 = Velocity x Weight
and since.... Momentum ~ Velocity x Weight
then.... Volume ~ Momentum
Bob
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The soap is outside the OP's question also, since he asked which would penetrate deeper in wood...
I guess we'd have to know what kind of wood, and how far away(or how fast at impact).
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since he asked which would penetrate deeper in wood...
I guess we'd have to know what kind of wood, and how far away(or how fast at impact).
Yup... exactly. Shoot a piece of balsa, apple, some cedar, and osage orange. Even a piece of pine can have variance- not just one piece to another, but one end of a board to another, especially if there are knots or heartwood involved. Even getting into the spacing of annular rings can impact penetration in wood.
It's why I ignore wood tests completely. If I'm looking for a good "test" of a pellet, I apply the pellet at the intended speed to the pest's skull. Just because I shot the squirrel in the nugget doesn't mean I can do some extra tests :D
If I want penetration, an arrow or high-speed bullet is far better than an airgun. It's why I have always considered airguns more adept at dumping energy, especially since wadcutters and HPs work great at the distance I'm pesting.
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Yep, you're right.... and which part of the grain the pellet hit, as well.... Exactly why I use soap, it's consistent, and more similar to something you might care about the penetration of.... ;)
Also correct, it's the IMPACT velocity that matters, not what it started out at....
Ramin, to answer your precise question, and assuming you are using the impact velocity (ie point blank range if that is the MV).... and further assuming that the wood is completely uniform in density, hardness, and grain structure, so that the impacts meet identical resistance.... the caliber is the same, so not a factor.... all that remains is the weight times the velocity....
25 gr. @ 910 fps = 22750
34 gr. @ 810 fps = 27540
so the 34 gr. @ 810 fps should penetrate about 21% further.... in theory.... even though it only has 7.7% more energy....
Bob
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Guys I shot a coke bottle at 130 yards today with my .25 wildcat, the impact was 18 fpe, and guess what... it didn't break it. it just hit it over.... I'm guessing the pellet wasn't hard enough? Never experienced anything that weird :/ Was using 25 grain JSB exacts.
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So should we also come to the conclusion that the same rifle that shoots the 25 grain .25 pellet @ 910fps, could not, in the same state of tune, push that 34 grain .25 pellet to the stated 810 fps?
I really don't know. But it would seem you'd need a different setup to only lose around 12% velocity when raising the weight by near 40%.
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Guys I shot a coke bottle at 130 yards today with my .25 wildcat, the impact was 18 fpe, and guess what... it didn't break it. it just hit it over.... I'm guessing the pellet wasn't hard enough? Never experienced anything that weird :/ Was using 25 grain JSB exacts.
Where do you get a glass coke bottle?
Was it a Mexican coke?
Anyway, I was shooting at a beer bottle with my 1377 a few weeks ago. And from about 18 yards, the first shot didn't break it. I think it was an off center hit, a glancing blow, because I heard the pellet go whizzing off to the left. On the second shot I took a little more care to make an on center shot and it broke.
Kinda felt bad after, as I don't like to break glass.
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39M, the specified velocities for the two pellets work out to 46 FPE for the 25 gr. and 49.5 FPE for the 34 gr.... PCPs generally gain a bit of energy without retuning when going to a heavier pellet, so it is likely you wouldn't have to change anything, or maybe just tweak the hammer spring preload a bit.... 46 FPE with the 34 gr. actually works out to 780 fps (instead of 810), and you almost never get less energy with a heavier pellet.... I would expect 790-800 fps with the 34 gr., but 810 is possible, it just depends on the actual tune involved....
If we assume the worst case, and use the 46 FPE (780 fps) for the 34 gr., doing the same math we get....
34 gr. x 780 fps = 26520.... compared to the 25 gr. @ 910 = 22750.... That still works out to about 17% more penetration predicted for the 34 gr. compared to the 25 gr.... My tests confirm that when the FPE is held constant, in the same caliber, heavier pellets tend to penetrate further.... because they have greater momentum.... ie reality matches theory....
Bob
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Guys I shot a coke bottle at 130 yards today with my .25 wildcat, the impact was 18 fpe, and guess what... it didn't break it. it just hit it over.... I'm guessing the pellet wasn't hard enough? Never experienced anything that weird :/ Was using 25 grain JSB exacts.
Where do you get a glass coke bottle?
Was it a Mexican coke?
Anyway, I was shooting at a beer bottle with my 1377 a few weeks ago. And from about 18 yards, the first shot didn't break it. I think it was an off center hit, a glancing blow, because I heard the pellet go whizzing off to the left. On the second shot I took a little more care to make an on center shot and it broke.
Kinda felt bad after, as I don't like to break glass.
it was a mexican coke, do you even realize how surprised I was when 18 fpe didn't shatter it lol?
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39M, the specified velocities for the two pellets work out to 46 FPE for the 25 gr. and 49.5 FPE for the 34 gr.... PCPs generally gain a bit of energy without retuning when going to a heavier pellet, so it is likely you wouldn't have to change anything, or maybe just tweak the hammer spring preload a bit.... 46 FPE with the 34 gr. actually works out to 780 fps (instead of 810), and you almost never get less energy with a heavier pellet.... I would expect 790-800 fps with the 34 gr., but 810 is possible, it just depends on the actual tune involved....
If we assume the worst case, and use the 46 FPE (780 fps) for the 34 gr., doing the same math we get....
34 gr. x 780 fps = 26520.... compared to the 25 gr. @ 910 = 22750.... That still works out to about 17% more penetration predicted for the 34 gr. compared to the 25 gr.... My tests confirm that when the FPE is held constant, in the same caliber, heavier pellets tend to penetrate further.... because they have greater momentum.... ie reality matches theory....
Bob
super interesting...
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Excellent! I knew that pneumatics in general respond well to higher weights. But had no idea that a powerful PCP air rifle could keep that kind of pace with heavier pellets.
Mr. Sterne, you truly are a wealth of knowledge and I appreciate the chance to absorb some of it.
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Here is some hard data for you.... JSB Exact series pellets, in .22 cal, fired from a PCP tuned for 20 FPE.... Penetration distance in soap, point blank range....
13.4 gr.... 79 mm
14.3 gr.... 87 mm
15.9 gr.... 93 mm
18.1 gr.... 98 mm
25.4 gr.... 106 mm
The 34 gr. Beasts were not available when I did those tests.... but the trend is obvious.... The heavier pellets, even though travelling slower, had greater penetration.... in accordance with their greater momentum....
Bob
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Here is some hard data for you.... JSB Exact series pellets, in .22 cal, fired from a PCP tuned for 20 FPE.... Penetration distance in soap, point blank range....
13.4 gr.... 79 mm
14.3 gr.... 87 mm
15.9 gr.... 93 mm
18.1 gr.... 98 mm
25.4 gr.... 106 mm
The 34 gr. Beasts were not available when I did those tests.... but the trend is obvious.... The heavier pellets, even though travelling slower, had greater penetration.... in accordance with their greater momentum....
Bob
See I was at the range today, I had my rifle chambered in .308 and my friend had his ar 15 in .223, now his rifle out penetrated mine and his argument was his bullet was going faster and my counter-argument was no it's because his bullet diameter was much less than mine. Good to know I was right :)
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Or maybe he was shooting FMJ ammo?
Or long for caliber bullets...high weight?
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Or maybe he was shooting FMJ ammo?
Or long for caliber bullets...high weight?
We were both using FMJ so I don't think it was that, his was shooting 77 grains at 2800 fps and I was shooting 185 grains at 2500 fps, so I had nearly double his energy.
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77 gr. in .223 cal has an SD of 0.221 x 2800 fps = 619
185 gr. in .308 cal has an SD of 0.278 x 2500 fps = 696
With equal projectile shape, construction, and hitting the same medium, the .308 should have had more about 12% more penetration.... That can easily be reversed by the other factors.... but it gives you an idea how to work stuff like this out.... Any expansion or yawing of the projectile after impact, changes things in a hurry....
Bob
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77 gr. in .223 cal has an SD of 0.221 x 2800 fps = 619
185 gr. in .308 cal has an SD of 0.278 x 2500 fps = 696
With equal projectile shape, construction, and hitting the same medium, the .308 should have had more about 12% more penetration.... That can easily be reversed by the other factors.... but it gives you an idea how to work stuff like this out.... Any expansion or yawing of the projectile after impact, changes things in a hurry....
Bob
Ya that's interesting aint it? It could have been so many aspects, my guess is my bullets might have went in an angle while his went straight, crazy how many aspects are in bullets and penetration.
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77 gr. in .223 cal has an SD of 0.221 x 2800 fps = 619
185 gr. in .308 cal has an SD of 0.278 x 2500 fps = 696
With equal projectile shape, construction, and hitting the same medium, the .308 should have had more about 12% more penetration.... That can easily be reversed by the other factors.... but it gives you an idea how to work stuff like this out.... Any expansion or yawing of the projectile after impact, changes things in a hurry....
Bob
Ok can you explain to me how 18 fpe didnt crack nor go through a mexican coke? I didn't even see a mark on it.
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77 gr. in .223 cal has an SD of 0.221 x 2800 fps = 619
185 gr. in .308 cal has an SD of 0.278 x 2500 fps = 696
With equal projectile shape, construction, and hitting the same medium, the .308 should have had more about 12% more penetration.... That can easily be reversed by the other factors.... but it gives you an idea how to work stuff like this out.... Any expansion or yawing of the projectile after impact, changes things in a hurry....
Bob
Ok can you explain to me how 18 fpe didnt crack nor go through a mexican coke? I didn't even see a mark on it.
I think ya missed an it went a wizzin of a rock.. ;)
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77 gr. in .223 cal has an SD of 0.221 x 2800 fps = 619
185 gr. in .308 cal has an SD of 0.278 x 2500 fps = 696
With equal projectile shape, construction, and hitting the same medium, the .308 should have had more about 12% more penetration.... That can easily be reversed by the other factors.... but it gives you an idea how to work stuff like this out.... Any expansion or yawing of the projectile after impact, changes things in a hurry....
Bob
Ok can you explain to me how 18 fpe didnt crack nor go through a mexican coke? I didn't even see a mark on it.
I think ya missed an it went a wizzin of a rock.. ;)
haha xD Nah man hit it dead on @ 130 :) through that thing but I swear didn't even leave a mark on it lol... JSB 25 grains too soft I guess :/
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Hit a thick part of the bottle, no different than a rock hitting your windshield.... The angle and relative strength is everything....
Bob