GTA
All Springer/NP/PCP Air Gun Discussion General => PCP/CO2/HPA Air Gun Gates "The Darkside" => Big Bore AirGun Gate => Topic started by: Tiroflojo on March 22, 2019, 11:40:56 AM
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This is a question for the ballistics experts: After doing my tests with the Condor 30 of different design and weight bullets (they have not finished yet), I have the question of whether the final effect of the impact of a 75 grains bullet on 309 mx sg compared with that of another bullet from 140 grains to 198 mx sg, is it the same, very similar or very different ????
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I am not familiar with the term "mx sg"....
Bob
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I am also not familiar with the term, however, If driven at an fps that gives both bullets similar fpe, the lighter bullet will have greater expansion, wile the heavier bullet will have greater penetration. ;)
Knife
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That is correct, Michael.... and for non-expanding bullets that don't tumble in the target, the penetration is proportional to the Momentum, rather than the Energy (FPE)…. The velocity is not squared in calculating the Momentum (it is simply mass x velocity), so for equal energy, heavier bullets will have greater Momentum.... The wound channel volume, on the other hand, is roughly proportional to the FPE.... so the faster, lighter bullet (with the same FPE) will have a shorter, wider wound channel (even without expansion)….
Bob
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I'm going out on a limb to guess your translator is messing up that 309 mx sg and you meant to say 309 mps? Meters per second.
If that's the case they are not compatible. 309 mps 75 grain pellet is making 170 FPE, foot-pounds energy, or 230 joules. 140 grain at 198 mps is only 131 FPE, 177 joules.
If from the same gun and losing that much energy then the 140 grain is too much weight for the gun. Joules produced should go up as grain weight increases to a point where the gun just can't push it and the energy output plummets. Try a lighter slug like 100 to 110 grain.
Or I'm way off on what mx sp is.
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Thanks for the answers.
I think that for what you say is more interested in a heavy bullet, although somewhat slower, than a light weight and high speed.
My apologies for the term "m x sg": meters per second. As a European I am not familiar with "fpe" and "fps". We measure in meters for second speed and in joules of power.
Mr. Garret, you have made a very exact judgment. ;)
Not knowing their language and the "Imperial Measures" do not make it easy to understand or a good expression. But I try.
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Assuming that neither bullet expands or tumbles, and they are the same caliber, the penetration will be roughly proportional to the Momentum.... while the volume of the wound cavity will be roughly proportional to the Energy....
75 gr. @ 309 m/s
Energy = 0.00486 kg x 309 m/s x 309 m/s / 2 = 232 joules
Momentum = 0.00486 kg x 309 m/s = 1.50 kg.m/s
140 gr. @ 198 m/s
Energy = 0.00907 kg x 198 m/s x 198 m/s / 2 = 178 joules
Momentum = 0.00907 kg x 198 m/s = 1.80 kg.m/s
Therefore, in relative terms, in a consistent medium, the heavier, slower bullet will penetrate roughly (1.80 / 1.50) = 20% further....
However, the volume of the wound channel for the lighter, faster bullet will be roughly (232 / 178) = 30% larger....
Bob
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Thanks Bob, very good lesson.
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I guess those two slugs were closer to terminal power than first glance.
But you see what I mean if they were shot from same gun then the 140 grain is far too heavy. If same gun there is a point where joules produced will stop increasing at a certain grain weight. The gun is maxed out. Without calculations and a good guess- you should be over 240 joules with 115 grain. That would be great increase of terminal value of slug from the 75 grain. Assuming same gun of course.
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Not sure about 340 Joules.... but with the 75 gr. hitting 230 Joules, with a bit more dwell the 140 gr. should definitely be more energy.... 10% would be a reasonable guess, or 250-260 Joules....
Bob
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there you go Guy's. You both did a fine job of dissecting it and laying it out for Poster. 8)
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...the volume of the wound cavity will be roughly proportional to the Energy....
...the volume of the wound channel for the lighter, faster bullet will be roughly (232 / 178) = 30% larger....
When I was grabbed by the hollow point fever, I read quite a bit on wounds, death, and all that wonderfully morbid stuff that terminal ballistics is made of. 8)
If I remember right, there was an article that distinguished between a permanent wound channel [cavity] and a temporary wound channel. Bob, I'm just trying to understand -- are you referring to any one in particular?
Oh, I found the article (link below).
This trauma researcher (what a profession...!) writes on page 7:
“A large slow projectile (Fig 7) will crush [or lacerate] (permanent cavity) a large amount of tissue, whereas a small fast missile with the same kinetic energy (Fig 4) will stretch more tissue (temporary cavity) but crush little.”
It seems that WHAT KILLS is the permanent cavity, especially since our slow puny pellets don't induce this often-talked-about-yet-contested "hydrostatic shock" that a temporary cavity might induce.
Source: Fackler, Martin L. (1987). What’s wrong with the wound ballistics literature, and why. Institute Report No. 239. Letterman Army Institute of Research, Division of Military Trauma Research. July 1987.
http://rkba.org/research/fackler/wrong.html (http://rkba.org/research/fackler/wrong.html)
The two pics (4 and 7) are at the very end.
He's got another article (with pics) here: https://web.archive.org/web/20120218212956/http://ammo.ar15.com/project/Fackler_Articles/effects_of_small_arms.pdf (https://web.archive.org/web/20120218212956/http://ammo.ar15.com/project/Fackler_Articles/effects_of_small_arms.pdf)
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Whether the cavity is temporary or permanent has a lot to do with the consistency of the material being impacted... the softer it is, the more it collapses back into itself.... Have you even seen a permanent wound channel in liquid water?.... The soap I use collapses little, ballistics gel a lot more, water completely, bone not at all.... Remember, the guidelines I gave assume a non-expanding projectile that has not tumbled.... Both of those reduce the penetration but increase the wound diameter....
Bob
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Yeah, I get that, expanding and tumbling would crush and lacerate a wider permanent cavity, but that will slow it down quicker so it won't go so deep. => Wider, but shorter cavity, hopefully reaching the vitals
And the medium through which the projectile goes, yeah, that makes sense, if it's bones there's not much "collapsing back"!
I think the studies referred to all assumed wound cavities in more or less uniform soft tissue, without introducing the complicating factors of bones.
I found the last sentence here on page 8 interesting (Fackler, 1987): “Many body tissues (muscle, skin, bowel wall, lung) are soft and flexible – the physical characteristics of a good shock absorber. Drop a raw egg onto a cement floor from a height of 2 m; then drop a rubber ball of the same mass from the same height. The kinetic energy exchange in both dropped objects was the same at the moment of impact.
“Compare the difference in effect; the egg breaks while the ball rebounds undamaged.
“Most living animal soft tissue has a consistency much closer to that of the rubber ball than to that of the brittle egg shell. This simple experiment demonstrates the fallacy in the common assumption that all kinetic energy ‘deposited’ in the body does damage”.
Instead, “the critical issue here is what sort of hole are we making.”
Still trying to wrap my head around this. I read so much about "dumping all the energy into the quarry" – and it sounds intuitively correct, and it sounds cool when I say it.... ;D
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It does sound cool.
Dumping all the energy in the animal relates more to the alternative of pass through with little resistance. If you have overwhelming energy and use a round nose projectile it passes through animal and continues on. That is wasted energy. The round nose "slips" through flesh easily and the majority of wound channel closes back up. If you use a wide flat nose it's crushing, using more energy in body and causing a permanent wound channel. HP's speak for themselves.
Research I've read agrees with the old adage- you want a pass through. The research shows wound channels bleed more on exit side. Black powder and round ball choice was largest caliber ball that was retained on hide on exiting body 50% of the time. Meaning they wanted pass through 100% but using the largest caliber possible. Roundball don't leave large wound channels. The flesh is elastic. Flat nose leave permanent channels larger than the diameter of flat nose.
That's where hollow points are tricky. Fragmenting, explosive point is well and good for varmint. Larger game and low power guns this can't be achieved. The hollow point should be slow to expand for maximum penetration. Pass through and large permanent wound are the goal. A quick to mushroom or fragment bullet may not even penetrate to the heart of a large deer so you only made a big hole in one lung. For faster kill and more bleed out you want both lungs with exit hole. Shallow cavity HP that expands a controlled percentage more than caliber, a cup/dimple tip HP would be better choice or a deep narrow HP with thick side walls that makes it through ribs mostly intact to continue through animal with little expansion to push out ribes other side opened up more. Big hole on exit. Dumps all energy in animal as that bullet would fall to ground or be stuck under hide. Matching HP to gun and size of game would be hard to do.
Larger than coyote, go with a large mepait (flat nose). Best odds for desired result. Humane terminal ballistics.
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Not sure about 340 Joules.... but with the 75 gr. hitting 230 Joules, with a bit more dwell the 140 gr. should definitely be more energy.... 10% would be a reasonable guess, or 250-260 Joules....
Bob
Oh my, that was a typo. Edited to fixed it. I meant to say over 240 joules. Your estimate of 250-260 sounds very reasonable. That's for 140 grain, a 110-ish grain seems maxed weight gun. Unless there is another reason the energy dropped so much on the 140 slug. Improperly sized?
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It is open to argument, once you get into the "practical" side of wound cavities.... penetration vs. explosive expansion, etc.etc.etc…. because there are so many wide and varied theories.... A couple of the African guidelines for how to assess the killing power of a bullet on "dangerous game" place a baseball thrown by a professional pitcher at greater knockdown power than any bullet ever used on Elephant.... so flawed are the criteria used for the calculation.... or rather what they ignore....
I agree that a large hollowpoint is probably not a good idea on deer.... For a non-expanding bullet, larger is better, provided the penetration is enough to provide a pass-through.... I do agree that a pass-through on a deer is a good idea, for both faster bleed-out and easier tracking for those that don't drop on the spot (two holes are better than one).... and for the same reason, bigger holes, both entry and exit, are better as well.... A large Meplat allows a smaller caliber to create a larger diameter wound channel than the caliber would suggest.... I have never seen a complete study on it, but I would bet that you could correlate Meplat diameter in a given caliber to what a roundball in a large caliber would do, at the same velocity.... For instance, you can probably come to a conclusion that (for example) a 70% Meplat on a .357 cal bullet, with the same mass and velocity as a roundball in .457 cal. (143 gr.).... would both have the same wound channel diameter and penetration....
This seems to counter my previous argument that penetration for non-expanding projectiles is proportional to the product of the SD and velocity, but it really isn't.... The bullets have the same momentum, energy, mass and velocity.... but the .357 has a higher SD, so you would expect greater penetration.... However, the Meplat pushes the tissue out of the way in a different manner, and the flat base of the bullet travelling through the flesh may create more drag.... so the wound cavity tends to be larger, relative to the caliber…. The net result is that the "hole" (ie the damaged tissue) created by the .357 bullet passing through, because of its shape, ends up being the same diameter as that of the .457 roundball…. Since the same amount of tissue is displaced, and the bullets are the same mass and velocity, they end up having the same penetration.... and therefore identical wound cavities, both in shape and volume....
I don't know what Meplat diameter is required for this to occur, it may be 50%, 60%, 70% or 80%.... but I'm guessing it won't be 100% (a cylinder)…. It will, of course, depend on the medium used to test the hypothesis.... Ballistics gel may give a different answer than soap, wax or wood (which are progressively harder, in that order)…. The alloy the bullet is made from is another variable, as a bullet with a Meplat tends to flatten more on impact (becoming more cylindrical, or even larger at the front)…. and softer bullets require less velocity to do that, or expand more for a given velocity.... The upper bullet in this photo is a .25 cal 51 gr. BBT with a 70% Meplat that impacted melt-and-pour soap at about 930 fps.... The lower bullet is the same bullet, but the 47 gr. HP version at about 960 fps....
(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)
Here is a photo of the cavities created in the soap in the above test....
(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)
and here is the HP cavity cut open, with the fragments still in place....
(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)
Your choice of bullet design will obviously intend on your quarry.... That HP would expend most if not all its energy inside an animal the size of a Marmot or Woodchuck.... However, if you wanted to take a Coyote and needed the penetration.... or shoot a Hog in the head and needed the ability to penetrate a thick skull, the FN with the large Meplat would be your choice.... In a larger caliber, the same thing would apply to a deer.... I have done a lot of testing in soap, and a large, well designed HP tends to cut the penetration roughly in half.... Whether or not the HP fragments depends primarily on the depth of the HP cavity (deep ones tend to come apart), the velocity and the bullet alloy…. I have never done any testing with one, but the "cup point" pins (a short, cone shaped HP) supplied by NOE with their RG series moulds, could be ideal for deer hunting, creating some expansion without any danger of the bullet coming apart.... They are shown in the center in the photo below....
(http://i378.photobucket.com/albums/oo221/rsterne/Bullet%20Casting/HP%20Pins_zpsrifuvqvu.jpg) (http://s378.photobucket.com/user/rsterne/media/Bullet%20Casting/HP%20Pins_zpsrifuvqvu.jpg.html)
Assuming you have a gun that will drive them right through 50% of the time, or at least to the hide on the opposite side.... they could be an excellent choice for deer hunting....
Bob