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Posted: 6/13/2003 8:21:07 AM EDT
[#1]
Jacket thickness has something to do with it. M193 type and SS-109 projectiles beak apart at the cannelure, where the jacket is the thinnest.
HPBT Match bullets have thin jackets as well, but are also longer, meaning the 'force exerted on the bullet when it yaws is greater. If I am incorrect, Brouhaha or Troy will be along shortly to correct me. |
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Posted: 6/13/2003 8:28:43 AM EDT
[#2]
You are not talking about hollow points.
The 75 and 77 grain ammo is OTM or open tip match. The jacket is applied from the bottom of the bullet to get optimum accuracy. The hole in the tip is a by product of the manufacture of match rifle ammo. It does not function as a hollow point of traditional design. The jacket cover s the bottom to prevent bullet base deformation and aid accuracy. This is why (non fuctioning hollow tip) its legal for our military to use. Traditional hollowpoint ammo open up from the fluid pressures exerted inside the tip and break up/expand due to the hydrolic pressures involved. A FMJ 75/77 grain bullet would be long like the OTM bullets. The reason the OTM bullets fragemnt is that the are very long compared to length and therefore unstable. This is why they require a tight twist to be accurate. The longer the bullet is the more stress is placed on the bullet. This is why they fragment so readily. The match bullets have very thing copper jackets. This prevents the bullet from staying together as it yaws near 90 degrees. If it had a steel jacket or a very thick jacket it would not fragment. Traditional FMJ bullets have jackets applied from the tip and are open at the base instead of the tip. You usually end up with lead "squeezing" out the hole in the base if it does not fragment. To answer your question a FMJ 75 grain ammo would fragment like the 75 grain OTM if it had a jacket as thin and weak. However it would be FAR less accurate due to how the pressures would deform the base of the bullet and how that would affect gas release as the bullet exited the muzzle (but that is another longer story) Did this answer your question? If you have more questions please feel free to ask. |
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Posted: 6/13/2003 8:52:50 AM EDT
[#3]
Excellent responses, thanks guys.
So the OTM or open tip in the 75/77 gr bullets has nothing to do with fragmentation? Jacket thickness and adding a cannelure make sense for enhanceing the ability to fragment when the bullet yawns (especially with these long heavy bullets). Although,It seems like the first force when the bullet hits would act upon the weaker open tip. With my Hornady 68gr BTHP, if I stick something down into the hole there is a good quarter inch of empty space, and around the tip of the bullet there are lines running up and down I assume to aid in the point opening up. The hole point itself has a "serrated" pattern that also looks like it is to aid in expansion. I've never seen the heavy OTMs. I assume they to do not have these characteristics for reasons DevL mentioned (Geneva yada ya). |
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Posted: 6/13/2003 9:40:28 AM EDT
[#4]
The Hornady 68 grain bullet is also an OTM design just like the 75 grain Hornady bullet. The lines you see is how the bullet is formed over the lead. The 75 grain ammo also has the same air pocket at the tip. Upon impact the nose will crush down but the tip in both bullets lacks the design to get it to open up. The lead is essentailly flat at the bottom of that cavity. It would need to be concave and extend to the tip to allow fluid pressure to open it up.
Your Black Hills 68 grain is in fact OTM. Its a smaller version of the 75 grain ammo and acts in much the same way in terms of both accuracy and termianl effects. Bieng shorter it is more stable and the pressures exerted are less so it will not have as dramatic an effect or fragment at as low of a velocity but it is more stable and accurate out of a 1/9 twist barrel. The OTM were not designed to meet Geneva Convention standards. It was discovered after the fact that it was better at fragmenting. The rounds were developed strictly to be as accurate as possible. Everything about the bullets shape and construction has to do with accuracy not terminal effects. These effects were not even understood until recently. |
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Posted: 6/13/2003 9:51:24 AM EDT
[#5]
Just get a 15-20 gallon drum, fill it with water, and shoot straight down into the water.
Where I do it at, I can stand in the upstairs window, and fire straight down. I took and shot (2) 55gr SP speers, from a 11.5", 2615 avg, and (1) 52gr Hornady HP, 2535 avg. The 2 in the pic at left are the 55's, the debris at the right is the 52 HP, the top is a 270 Ballistic Tip recovered from a deer, and the bottom 2 are 9mm Gold Sabers from an Uzi 10". [img]http://www.imagestation.com/picture/sraid65/p1b0135a0fe2757a44f1234d41570e6ad/fbf2258f.jpg[/img] |
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Posted: 6/13/2003 10:19:30 AM EDT
[#6]
Thanks DevL, I guess I was mislead by the classification of the 68gr BT (hollow point). I certainly was aware that these heavier HPs were completely designed for accuracy. So that makes sense.
What do you mean when you say. This is why (non fuctioning hollow tip) its legal for our military to use. But... The OTM were not designed to meet Geneva Convention standards. Do you mean, they weren't designed to be meet the standards, but they do? Okay so here's an interesting test (maybe irrelevant but interesting non-the-less). I can take a PMC 55gr BT-FMJ and shoot a milk jug at 100yds. The bullet will pass right through leaving two small holes and no fragmentation (the bullet is probably only going about 2500fps at 100yds). NO suprise. I will then take the same type of bullet and barely snip the tip off with wire cutters (I did this before I realized that this could cause a jacket seperation inside the barrel, so I don't do it anymore). Then I shoot another jug at 100 yds, and the bullet/jug explode with massive fragmentation. So in this case only adding a small hole to the tip of the bullet is the difference between fragmentation and no fragmentation. I'm not sure if this would apply to heavier/longer bullets for the reasons stated above. But I'm curious if it would. Or if the hollow tip contributes more than expected. BTW, I couldn't find any related topics in a search so,if I'm rehashing something that has been discussed over and over or [beathorse]. Feel free to let this thread die. I hope this is a fairly fresh discussion. |
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Posted: 6/13/2003 11:10:28 AM EDT
[#7]
The hollow tip on HPBT Match bullets tends to shift the center of gravity toward the rear in the bullet, thus forcing the yaw of the bullet to happen sooner.
In the case of your 'tube' cut-off bullets, you are weakening the jacket of the bullet enough to force fragmentation sooner and at slower velocities than before. As I warned you in a past thread, and you picked up on, this practice is dangerous. However, there are varmint bullets that are made to function in this manner. The difference is, varmint bullets are generally closed at the base, and are of similar jacket construction to a HPBT Match bullet. The hollow tip of the bullet may indeed help the jacket be compromised in some situations, but try this: Fire a 52 grain Speer HPBT Match bullet at 1/4 inches of scrap metal. The bullet functions exactly like a Winchester FMJBT bullet. The hollow tip on the Match bullet does not aid in expansion in this scenario. The KEY to the damage done by heavy Match rounds is a function of jacket thickness and BULLET LENGTH. Long bullets will buckle, regardless of where the 'hole' is, causing a lot of little pieces of metal to break off. |
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Posted: 6/13/2003 11:18:45 AM EDT
[#8]
Ridge,
The context that most of us use when refering to bullet wounds is "how does the bullet act/perform in FLESH", or at least, in flesh simulant like 10% ballistic gelatin. Plastic jugs of water cannot in any way be compared to performance in flesh/gelatin. That doesn't mean that it isn't fun to shoot them, it just means that you really can't get any meaningful information about their performance in flesh from shooting them. The point I'm trying to make is that bullets perform VERY differently depending on the medium they are hitting. Folks often confuse "armor-piercing" and "body-armor" too, even though "armor-piercing" is talking about shooting through metal armor, and has no relation to soft body armor such as Kevlar or Spectra. To answer your question about why the bullets fragment, it's the same reason why the space shuttle disintegrated in reentry: FRICTION. When the bullet hits flesh, a medium 400 times more dense than flesh, it is suddenly not spinning anywhere near fast enough to remain stabile, and since the center of mass of the bullet is to the rear of the center of the bullet's length, the bullet will begin to yaw to try to put the center of gravity in the front. But the bullet only gets about halfway around when the friction on the bullet from trying to move sideways through flesh overcomes the structrual integrity of the bullet jacket. At this point, the bullet will fragment, as you see in the pics, and will shred the flesh inside the wound. Of course, many things can prevent fragmentation from occuring. If the bullet is going to slow, if the jacket is too thick, or if the jacket is made with material stronger than guilding-metal (a copper alloy that's standard bullet-jacket material), then the bullet will simply rotate the entire 180 degrees and will stop or exit base-first. It's been found that the heavy match bullets, being both long and having thin jackets, fragment very reliably even at lower velocities. This provides increased fragmentation range, especially from shorter-barreled rifles, than does standard M193 or M855 rounds. To learn more, check out [url]www.ammo-oracle.com[/url]. -Troy |
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Posted: 6/13/2003 12:04:51 PM EDT
[#9]
I've read the ammo oracle(a few times). I know WHY bullets fragment.
My questions was HOW a HP or OTM fragments. If it is related mostly to the yawning because of the center of gravity then breaking because of the thin jacket etc. etc., Or if the hollow tip (Or open tip) played a larger role in fragmentation like lighter hollow points. Good point on the jugs, I was only stating that I could get a FMJ to fragment at low velocity by adding a hole. Probably no ballistic significance without using gelatin. Just a tid bit. All excellent points! [b]Your all convincing me.[/b] Crap, I wish I had something more significant than milk jugs, but consider this. I'm pretty sure it has been established that MOST FMJ .308 will enter yawn and exit backward with no fragmentation. I think it has also been established that a .308 BTHP will fragment violently when it enters(This has been verified by my super scientific jug tests [:D]). So the point here is. This bullet is moving slowly (so velocity is probably not a factor). These bullets are not long and skinny (to completely take length out of the equation consider only a 150 or 155gr) like the .223. The .308 match bullets are probably designed and manufactured the same way the .223 match bullets are (being OTM not HP). So does the addition of an open tip facillitate fragmentation of these rounds, or does a 155gr BTHP yawn and break like the 75 gr OTM? I might have answered my own question on this, but we'll see what others have to say. |
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Posted: 6/13/2003 12:39:43 PM EDT
[#10]
yawn YAW as in 'pitch and yaw', not yawn as in the act of yawning. |
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Posted: 6/13/2003 2:21:40 PM EDT
[#11]
Quoted: So the point here is. This [.308] bullet is moving slowly (so velocity is probably not a factor). These bullets are not long and skinny (to completely take length out of the equation consider only a 150 or 155gr) like the .223. The .308 match bullets are probably designed and manufactured the same way the .223 match bullets are (being OTM not HP). So does the addition of an open tip facillitate fragmentation of these rounds, or does a 155gr BTHP yawn and break like the 75 gr OTM? Velocity is always a huge factor, and I'm not sure why you think a .308 bullet "won't be moving very fast." .308 match bullets fragment the same way and for the same reasons that 68-80gr .223 match bullets do. The open tip's contribution is strictly limited to putting the center of gravity a bit further to the rear than it would be already. -Troy |
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Posted: 6/13/2003 3:34:48 PM EDT
[#12]
Yes I mean that the bullets were not designed to be legal in war but do meet the qualitfications anyway.
German NATO .7.62mm ammo fragemnts due to its weaker jacket than US NATO 7.62mm ammo. If you closed the tip of a match bullet it would still fragment at the same velocity. If you snip the tip of a FMJ you may cause it to shed its jacket and cause a hydro static effect to blow up a water bottle but this does not make it fragment in flesh more reliably. It will end up like a lead bullet in flesh. You would have the same effects with an all lead bullet. Lead is easily deformed. This tip cutting also could also reduce the penetration of both soft tissue and barriers. |
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Posted: 6/13/2003 4:37:56 PM EDT
[#13]
Quoted: Yes I mean that the bullets were not designed to be legal in war but do meet the qualitfications anyway. Got it. German NATO .7.62mm ammo fragemnts due to its weaker jacket than US NATO 7.62mm ammo. Ya, I thought of the German 7.62 as I was writing my question. Jacket thickness is the key. If you closed the tip of a match bullet it would still fragment at the same velocity. If you snip the tip of a FMJ you may cause it to shed its jacket and cause a hydro static effect to blow up a water bottle but this does not make it fragment in flesh more reliably. It will end up like a lead bullet in flesh. You would have the same effects with an all lead bullet. Lead is easily deformed. This tip cutting also could also reduce the penetration of both soft tissue and barriers. Excellent point!! @Troy I consider .308 (2800-2600 fps)to be slow for a .30 cal bullet/cartridge. |
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Posted: 6/13/2003 7:24:52 PM EDT
[#14]
Quoted: My questions was HOW a HP or OTM fragments. If it is related mostly to the yawning because of the center of gravity then breaking because of the thin jacket etc. etc., Or if the hollow tip (Or open tip) played a larger role in fragmentation like lighter hollow points. I believe that HP bullets, for the most part, are not supposed to fragment, but expand. Both HP and SP bullets should expand rapidly from the tip to mushroom out by design. The effect is more pronounced in HP bullets which initiate expansion faster. It basically depends on what you're trying to accomplish. Varmints = rapid expansin = HP is the commonly accepted formula. It appears that some HP bullets, mostly the smaller calibers like some 223's, are designed not only to expand, but to fragment as well. The ammo oracle lists that M193 ball fragments down to ~2700fps. HP ammo should still fragment at even lower velocities, since you're not depending on jacket integrity at a certain yaw angle and velocity to allow for fragmentation. I bet that bullet designers for small caliber HPs design them specifically to take out small varmint-type critters, where you want very rapid expansion, and they probably make the jacket thin enough to fragment on top of that. You're likely to not be interested in salvaging meat in that case. Small calibers are also used for some small game, where you might want a SP which has adequate penetration, and I bet these won't fragment by design. I'm not convinced that HP's of a larger caliber are designed to expand rapidly AND fragment, but I kind of doubt it. Most HP bullets in larger calibers are for match shooting. You wouldn't shoot a game animal with one, since the bullet may not penetrate sufficiently. This explains why all hunting bullets you see are usually of the SP variety - it makes for slower expansion which allows better penetration. As far as HOW HP's start to fragment - it intuitively makes sense that the forces acting on the hollow point cause the jacket to peel back in a predictable manner, but you'd need someone good in fluid dynamics to talk more about that. I'm just a dumb electrical engineer.... |
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Posted: 6/13/2003 9:40:35 PM EDT
[#15]
zhukov,
There are certainly hollow-point .223 bullets designed to expand exactly as you describe, and you are right in that they are designed primarily as varmint bullets. The rounds we were talking about are not these, though. We were talking about match bullets that, due to their need for a uniform base, end up having an open tipped bullet jacket due to the core being inserted in the jacket base-first. These bullets were NOT designed to fragment, expand, or do anything but be accurate when punching holes in paper at long distances. It just so happens that some of the characteristics that make the bullet accurate also help to make it fragment in tissue, provided that there is enough velocity, and the tissue is deep enough. M193 is the same, in that it wasn't *designed* to fragment, and in fact, no thought was given to that at all. The fact that it does fragment is just a "happy little accident." -Troy |
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