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Posted: 4/7/2006 4:32:40 PM EDT
This is a bit of jmart stream of consciousness, so please humor me a bit.

We've all seen this Frag Chart. We have it committed to memory, we consider it absolutely critical in our thought process as we debate effectiveness of various loads and barrel lengths for self defense applications. It is our mantra.

We also seem to universally accept that the 12-18" penetration depth in gel is what we need to strive for. I've seen several heated debates on how loads which fail to meet this threshold are categorically slammed, and folks who ask questions about them are advised very strongly to avoid their usage. 12-18" too is our mantra.

But I've never seen anything that marries up the two.

All the ballistic gel testing measures penetration depths at distances and velocities not to far beyond the muzzle. We applaud M193 for meeting penetration depth thresholds and then in the next breath we proclaim that based on it's frgamentation threshold it's good out to 100+ yds or so, depending on barrel length. But I've never seen penetration depth testing at the max range associated with a load's/barrel length's frag velocity threshold. Consequently , I wonder if we are kidding ourselves that just because a load tests nicely at 15 ft from the muzzle, that we can assume it will penetrate sufficiently out past 100 yds. I suspect that it won't based on a photo I saw of M855 penetration depth at 100 yds, it wasn't all that great. But at the same time, if we know from empirical evidence that various loads remain effective at ranges beyond which 12" of penetartion is achieved, are we placing too much empahasis on penetration?
Link Posted: 4/7/2006 4:52:17 PM EDT
I could have sworn Brouhaha did test ammo at the frag threashold to demonstrate the penetration/fragmentation at the threshold.

Not on his site now, for sure.
Link Posted: 4/7/2006 5:05:18 PM EDT
[Last Edit: 4/7/2006 5:07:31 PM EDT by WesDesRat]
I dont have a link handy but I know there have been tests of M193 bullets fired at varying velocities to determine the "threshhold" where they fragment...and there is a pic floating around here somewhere showing it. I imagine that other loads have been tested similarly as well.

ETA: IIRC it listed penetration depths, velocities, and showed the recovered fragments.

Link Posted: 4/7/2006 5:21:51 PM EDT
My recollection was that those tests tested the fragmentation and penetration at muzzle velocities, not frag threshold velocities, but I could be mistaken.
Link Posted: 4/7/2006 5:51:53 PM EDT

Originally Posted By jmart:
My recollection was that those tests tested the fragmentation and penetration at muzzle velocities, not frag threshold velocities, but I could be mistaken.



Well, a bullet traveling at 2500 fps at 150 yards should be the same as a bullet specifically loaded and fired at 2500 fps from a test barrel at ten feet. There shouldnt be a need to fire rounds over the full distance (100 yards, 150 yards, 200 yards, whatever the case may be) to replicate their fragmentation at certain velocities. Velocities can be tweaked and changed by loading a test barrel with a downloaded cartridge to achieve the "target" velocity.

Also as distance increases, the necesity of full penetration and/or fragmentation becomes less of an issue than if you are facing someone at spitting distance.

Keep in mind that when most .224" bullets dont fragment, they penetrate deeper because they retain more weight. While they may not be as effective as when they fragment at closer range, they should, if placed well, be capable of producing a leathal wound.

Make sense?
Link Posted: 4/7/2006 8:41:52 PM EDT
Makes some sense. I realize your point about adjusting muzzle velocity downward to simulate penetration at distance, I'm just saying my recolelction was that bullets were fired at 3,000 fps or greater muzzle velocity and those were the ones that were posted, with penetration depths catalogued.

Link Posted: 4/8/2006 8:38:49 AM EDT
Link Posted: 4/8/2006 8:51:34 AM EDT
A couple more questions:

Does a M193 or M855 round that tumbles, but doesn't fragment, does it make the 12" depth? If so, out to what range, say from a 16" barrel?

Is there an envelope where fragmentation occurs but depth is comaparatively shallow (undesirable), but once velocity decreases some more, fragmentation ceases but penetration depth increases back to the 12" desired depth (since the bullet is now holding together)? If so, what would be more desirable, say fragmentation with 8" depth or no frgamentation but 12" depth?

Also, does anyone have the BT Ammolab's tests of M193 gel pics saved off? Neither that test nor the M855 test are linked to their site anymore. From what I could tell about the other tests, they were run at full velocity rather than downloading to simulate impact at fragmentation velocity thresholds.
Link Posted: 4/8/2006 9:25:25 AM EDT
No they dont underpenetrate in military barrel lengths and they will reach 12" to a distance so far that accuracy, or even seeing a target, is more an issue than penetration. We are talking hundreds of yards from an M4 barrel.
Link Posted: 4/8/2006 10:10:29 AM EDT

Originally Posted By DevL:
No they dont underpenetrate in military barrel lengths and they will reach 12" to a distance so far that accuracy, or even seeing a target, is more an issue than penetration. We are talking hundreds of yards from an M4 barrel.



Interesting because the lone picture I have shows M855 penetrating about a max of 8" at 100 yds in gel. Barrel length and impact velocity is not mentioned.
Link Posted: 4/8/2006 12:28:06 PM EDT
[Last Edit: 4/8/2006 12:34:35 PM EDT by wyv3rn]
DevL's statement is 100% correct. Could you post that picture jmart? It might be one I'm familiar with and could fill in the story.

BTW, Brouhaha and Tatjana have tested M193, the Hornady 75gr and Nosler 77gr at multiple ranges, not all their testing is done at short range.
Link Posted: 4/8/2006 12:55:33 PM EDT

Originally Posted By wyv3rn:
DevL's statement is 100% correct. Could you post that picture jmart? It might be one I'm familiar with and could fill in the story.

BTW, Brouhaha and Tatjana have tested M193, the Hornady 75gr and Nosler 77gr at multiple ranges, not all their testing is done at short range.



Sorry, I can't post the pic, it's from a gun rag. Guns and Ammo Book of the AR-15. Several months old by now, it was copyrighted in 2005. I may have picked it up last summer even The pic shows a light weight varmint-type HP and a M855 round shot in gel at 100 yds. The varmint HP had very shallow penetration, just 3-4". The M855 penetrated to 8".

I wish I could remember (and access) Brouhaha's and Tatjana's test data. The BT Ammolab's links seem to have disappeared.
Link Posted: 4/8/2006 2:23:33 PM EDT
[Last Edit: 4/8/2006 2:26:57 PM EDT by jmart]
Here's some data from Fackler which many are familar with. It gives a good idea of a wound profile and penetration, but it appears to me that that chart is based on a profile achieved at an imapct velocity close to muzzle velocity. Also there's the added chart of bullet fragmentation given various velocities, but again, none of these are accompanied by penetration values.
Link Posted: 4/8/2006 3:00:10 PM EDT
since it's not fragmenting as much at longer distances, wouldn't it penetrate MORE despite the somewhat lower velocity, because the lack of fragmentation means greater retained weight and more energy used for penetration rather than dispersed into the surrounding flesh by fragmentation?
Link Posted: 4/8/2006 5:38:38 PM EDT

Originally Posted By fossil_fuel:
since it's not fragmenting as much at longer distances, wouldn't it penetrate MORE despite the somewhat lower velocity, because the lack of fragmentation means greater retained weight and more energy used for penetration rather than dispersed into the surrounding flesh by fragmentation?



That would seem to make sense, although I don't really have a good handle on penetration of a tumbling round. From what I understand the round will yaw and swap ends due to weight distribution, I believe this happens regardless of whether or not fragmentation occurs. I don't think it will tumble repeatedly though, I think it just does a 180 and then continues penetrating. As long as bone isn't hit I would expect it to track pretty straight once the rotation is completed, but given the initial yaw, that isn't always a straight line from entry to exit.
Link Posted: 4/9/2006 6:31:16 AM EDT
Link Posted: 4/9/2006 7:00:49 AM EDT

Originally Posted By Troy:

Originally Posted By fossil_fuel:
since it's not fragmenting as much at longer distances, wouldn't it penetrate MORE despite the somewhat lower velocity, because the lack of fragmentation means greater retained weight and more energy used for penetration rather than dispersed into the surrounding flesh by fragmentation?



Yes, to a point, and then, as distance increases (and bullet velocity decreases), penetration will start dropping. If you plotted it out, you would see a penetration spike that occurs once the bullet drops below fragmentation velocity, and then penetration depth would start falling off.

Folks, keep in mind that gelatin testing is labor intensive, stinky (gelatin stinks), and quite expensive. While it would be great to have a full suite of tests for each load, one full battery of tests could easily cost $40,000.

-Troy



Troy, thanks for dropping in, I was hoping you would see this and contribute. I realize testing isn't cheap and that Brouhaha and Tatjana can't cover every conceivable combination, but do you have access to any other data that demonstrates penenetration depths at various ranges/impact velocities? Maybe DocGR?
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