View Full Version : Is 6.8 a viable alternative to 7.62 for an MBR?
I'm not playing these calibers off against each other, just looking at it from the standpoint of a shooter who has multiple AR's in 5.56, bolt action rifles in 7.62, and wants to add a heavier caliber semiauto "MBR" type of battle rifle to the collection. Currently unable to afford both, but I'd like to start with an MBR for range shooting up to 600 yards, deer hunting (if I can keep it under 10 lbs), and of course defensive or "SHTF" operations.
I know the 6.8 does fine at deer hunting and range work, and the ballistics programs indicate it's good for paper punching up to 600 yards. But my questions are mostly on how the 6.8 compares to 7.62 as a battle round.
* Within that first 600 yards (which is probably the useful/practical range of the 6.8), how well does the 6.8 compare to the 7.62 at typical combat applications: CQB work, sniping, penetrating light cover, etc.? would the 7.62 likely be a lot more effective at things like penetration of cover within the first 300 yards? Are there any published studies by the military or anyone else comparing these rounds?
* What about beyond 600 yards? Obviously 7.62 NATO can still be effective out to 800 or even farther, depending on shooter, rifle, and glass. But is it possible to extend the effective range of 6.8 beyond 600 yards, if you have to?
* What do you think? If you had to pick 6.8 or 7.62 to start with as your MBR, given the pros and cons of both (a big pro of the 6.8, for me, is the fact it works on existing AR platforms and even my current lowers), which would it be?
Not what you asked but...
Do you have a use for 600+ yard shooting? Have you ever done it before? Do you have a location where you can do it regularly?
Think about your practical applications for what you're looking to buy/build and the answers should present themselves to you in short order.
Failure2Stop
08-12-08, 10:39
6.8 is a viable combat cartridge.
You seem to be fixated on "Assault" rifle versus "Battle" rifle terminology. As far as that goes the 6.8 is a very good assault rifle cartridge. That being said, the definition of a system is far less important than the individual employing said rifle. When someone defines the battle rifle as something that is effective at X distance, you must remember how that was achieved- mass volume fire. That employment technique is quite different than individual target engagement. There is a reason that no army in the world carries a "battle" rifle as the primary armament.
Maybe DocGKR can come in and get into the nitty-gritty.
Thanks for the replies. It's probably simpler to just remove my usage from the picture, and phrase the question I'm looking at in more general terms:
Does anyone have information (published content, first-hand experience, ballistics studies, whatever) on how effective the 6.8 is, compared to 7.62, as a combat cartridge used in the following scenarios:
* CQB
* Penetration of light cover (not really a separate scenario, but a factor that may apply in any of these other scenarios.
* Sniper/DMR use (at 600 yards or less, given that is often considered the practical effective range of the 6.8)
* Firefights with high round-counts (whether firing FA, select fire, or rapid-fire semiauto)
I've found the excellent articles on the 6.8 itself, including Zak Smith's articles, and some stuff by DocGkr on terminal effects of the 6.8 at Tactical Forums. But I haven't been able to find much specific evaluation of how the 6.8 stacks up to the 7.62 as a combat cartridge, focusing on the effectiveness of the two rounds (and NOT looking at peripheral advantages such as lighter recoil for the 6.8, even though such advantages are useful). Obviously a problem here is, only a few units of the military have allegedly evaluated it, and I don't know if that info is even available anywhere. In other words, there just may not be that much info out there yet, on the above questions.
Have you read this: http://www.dtic.mil/ndia/2008Intl/Roberts.pdf?
Thanks, DRGKR,
I never get tired of reading that presentation.
+1. Some interesting info, thanks for posting it.
One question came up in reading it: What is "fleet yaw"?
Fleet Yaw is the terminal performance AOA variation caused by inherent variability in each rifle; fleet Yaw is caused by weapon to weapon variations separate from projectile induced AOA issues. 5.56 mm FMJ had the most Fleet Yaw induced variability of any projectile caliber & type. 6.8 mm had the least Fleet Yaw variations of any projectile caliber & type tested.
Projectile impact angle-of-Attack (AOA) variability is caused by bullet to bullet variations at impact and can substantially wound severity; this factor is more prevalent with certain calibers and projectile types. Testing demonstrated that 5.56 mm is highly susceptible to AOA variations, particularly when using FMJ projectiles such as M193 & M855. For example, with 5.56 mm FMJ, at higher AOA’s, for example 2-3 degrees, bullets had a shorter neck length (NL) and upset rapidly, thus providing adequate terminal effects; at low AOA, like 0-1 degree, the projectiles penetrated deeper than ideal prior to initial upset (ie. long NL) with significantly reduced terminal effects. Note that other calibers were less susceptible to AOA variations than 5.56 mm and OTM’s tend to have less AOA issues than FMJ. The 6.8 mm has proved to have the least AOA inconsistencies of any caliber tested to date.
Again, both projectile AOA and Fleet Yaw appear much more prevalent in 5.56 mm, particularly with FMJ loads, than with larger calibers and match loads. These are clearly multi-factorial problems of multiple etiology including: ammo and weapon design issues, ammo and weapon manufacturing variations, individual weapon wear issues, along with both mechanical function and internal ballistics variances.
http://www.10-8forums.com/ubbthreads/postimages/40052-MilitaryAssaultRifleWPcopy.jpg
http://www.10-8forums.com/ubbthreads/postimages/40053-MilitaryRifleWPcopy.jpg
Have you read this: http://www.dtic.mil/ndia/2008Intl/Roberts.pdf?
Awesome, thanks.
I have actually never seen this before.
One question, has anyone revisited the 6.5 Grendel with some of the new loadings?
It would seem to me that if we were going to transition to a single caliber the 6.5mm would be better in the DMR and SAW role while still offering everything and more that the 6.8mm offers.
What are you trying shoot at 400, 500, 600yds? Paper? Deer? Something else?
6.8 isn't terribly flat. You'll have to know your range pretty precisely to hit at those distances. Miscalculate range by 50 yards and you'll be off significantly.
What optic setup do you intend to run?
What are you trying shoot at 400, 500, 600yds? Paper? Deer? Something else?
6.8 isn't terribly flat. You'll have to know your range pretty precisely to hit at those distances. Miscalculate range by 50 yards and you'll be off significantly.
What optic setup do you intend to run?
It's got a very flat arc out to about 400. I've got regular access to a 385 yard range and when shooting at a 12" plate at that range I don't even make adjustments (16" Noveske barrel, AAC M4-2K with SSA 115gr SMK's). I hold over at the top of the stand and make hits in the lower third of the plate. After that, ranging and dope start to become more important, but that is true for any cartridge.
Stephen
Have you read this: http://www.dtic.mil/ndia/2008Intl/Roberts.pdf?
I see something wrong with this chart.
They are overlaying the human body directly over ballistics gel results. 1" of ballistics gel does not equal 1" of human.
Failure2Stop
09-14-08, 16:32
I see something wrong with this chart.
They are overlaying the human body directly over ballistics gel results. 1" of ballistics gel does not equal 1" of human.
Source and scientific data support?
To raise the "BS Flag" on Dr Roberts' information makes you responsible to substiantiate your claims. While ballistic gelatin is not people-meat, it has proven to be extremely accurate in simulating tissue destruction, as proven by x-rays and autopsies, along with many years of data collection.
Please share the hard scientific data that disproves the findings of Dr Fackler, Dr Roberts, the FBI, and the rest of the research community at large when it comes to wound ballistics.
Source and scientific data support?
To raise the "BS Flag" on Dr Roberts' information makes you responsible to substiantiate your claims. While ballistic gelatin is not people-meat, it has proven to be extremely accurate in simulating tissue destruction, as proven by x-rays and autopsies, along with many years of data collection.
Please share the hard scientific data that disproves the findings of Dr Fackler, Dr Roberts, the FBI, and the rest of the research community at large when it comes to wound ballistics.
Never said this, but the FBI report released on "under penetration" does talk about the problem with gel = humans. Your putting words in my mouth.
I'm not saying gel doesn't give good information about how bullets behave. I'm stating that 1" of gel doesn't equal 1" of human. How do you think hollow points with over 12" of gel penetration wedge themselves shallow into people? Don't believe me? Look at the extremely graphic FBI power point on a recent shootout. They littered a mans body with .40 hollow points, and finally killed him with 5.56 TAP.
You can even read about gel calibration where a BB/Pellet gun is used to help normalize data.
Failure2Stop
09-15-08, 04:41
Never said this, but the FBI report released on "under penetration" does talk about the problem with gel = humans. Your putting words in my mouth.
Sorry, that's how I took your statement.
I'm not saying gel doesn't give good information about how bullets behave. I'm stating that 1" of gel doesn't equal 1" of human. How do you think hollow points with over 12" of gel penetration wedge themselves shallow into people? Don't believe me? Look at the extremely graphic FBI power point on a recent shootout. They littered a mans body with .40 hollow points, and finally killed him with 5.56 TAP.
Those .40s in the PPT came in from the side, performing just like they do in gel. Still, there are also anomolies in shooting people. Bones, intervening material, movement, and the plethora of other things that can happen in the course of a gunfight can obscure data and give impressions that are not necessarily correct.
The ballistic gelatin gives a very accurate (within a very small percentage) view of what the bullet is going to do in tissue. Bone is not dense enough to be a significant factor in calculating bullet performance. I have a theory that the various doctors that comprise the ballistics authority are aware that people contain bones, and found that it was not significant enough to standardize in testing as they have done with clothing, windshields, armor, etc.
Now, I am saying this from the understanding I have of wound ballistics from studying the work of Dr Fackler, Dr Roberts, and the IWBA. Any misunderstanding is my own mistake.
You can even read about gel calibration where a BB/Pellet gun is used to help normalize data.
I am quite familiar with the BB calibration method. 590 fps .177 projectiles can be counted on to break skin and shallowly penetrate tissue. Just like in ballistic gelatin. True, ballistic gelatin doesn not have skin to stop extremely low velocity impacts, but ballisitc testing does not occur at these low speeds.
I am not replying to this, nor the original post to try to make you look stupid or just to argue. I did it because I wanted to know what data you had to support your claim. You are not the only one to note this, I myself have stated it as well in the past. However, after extensive research into the matter I am satisfied that the difference is very small indeed.
I see something wrong with this chart.
1" of ballistics gel does not equal 1" of human.
Without warming up a cadaver and pumping fluid through it, ballistic jello is as good as it gets.
Without warming up a cadaver and pumping fluid through it, ballistic jello is as good as it gets.
That's true, but I don't think you should do a transparent overlay of a body on top of gel results. They give a good idea of a bullets reaction to soft tissue, but I wouldn't over lay the depth of a person.
Go to page 7, then tell me if you agree that this is a viable way to conclude 5.56 will exit before tumbling or fragmenting.
Many here are in the military or LE, so they have seen wounds in training, documentation and the field. Plus for civilians much of this is out there for us too, and medical journals document bullet wounds regularly. Real life data is important too.
I'm not saying gel doesn't give good information about how bullets behave. I'm stating that 1" of gel doesn't equal 1" of human. How do you think hollow points with over 12" of gel penetration wedge themselves shallow into people? Don't believe me? Look at the extremely graphic FBI power point on a recent shootout. They littered a mans body with .40 hollow points, and finally killed him with 5.56 TAP.
I hope you are not basing your comments on the leaked bastardized version of a FBI analysis of the PA fight, as that document is not complete. Even in the partial information available publicly, the x-rays depicted clearly show multiple expanded .40 caliber JHP's in the assailants body--all which appear to have penetrated substantially deeper than 1". More importantly, the FBI document unequivocally states that the Gold Dots satisfied FBI terminal performance requirements (ie. 12-18" penetration with acceptable expansion). It states that 5 of the 6 .40 JHP's recovered on autopsy were expanded (83% expansion rate) and that it is IMPOSSIBLE for .40 S&W JHP 180 gr ammunition to expand with 1" or less penetration in the human body. In short, when the FBI BRF tested the Gold Dots used in the incident, they behaved exactly the same in gel as they did in tissue...
As the FBI document states:
"There is plenty of inaccurate information regarding ballistics/terminal performance disseminated on web forums, even those which are dedicated as LE only.
----------------------------
The wound profile/anatomic overlay on page 7 of my NDIA briefing is completely consistent with the wounds seen OCONUS when M855 demonstrates a deep penetration prior to initial upset--these variations in neck length and the effects of AOA and Fleet Yaw first elucidated by the JSWB-IPT have been previously described multiple times, including above in the 8th post in this thread. Wound profile drawings illustrate the most commonly observed terminal performance, although all bullets routinely exhibit some degree of variation. The WP is typically made from shots into ordnance gel, but with the right imaging and autopsy technique, it could be done post-mortem, as there is a very high correlation between shots into properly calibrated 10% ordnance gelatin and shots in to living tissue. For example, refer to Wolberg's SDPD study comparing shots into gelatin with nearly 150 identical shots from OIS incidents. Wound ballistic researchers have been doing overlays like this for 20 years, starting with Dr. Fackler at LAIR, and they have proven to be very accurate. For example, on the last several LE rifle shootings in this area using Hornady 5.56 mm and .308 TAP loads, there was nearly 100% correlation between the gelatin derived WP's when overlayed on the CT's from the OIS incidents. At a briefing a year or so ago at Camp Pendleton for the I MEF SOTG, a SOF HMCS with 4 combat tours in OEF/OIF stated the wound overlays presented exactly matched his experiences treating combat wounds OCONUS. Pretty much every briefing I have given includes such imagery as it accurately and vividly depicts the results from rifle shots...
Hey fella's, keep it to the subject please--.308 and the 6.8. If you want to discuss the .40 and the Tap rounds in the PA shooting, take it to another thread on that issue.
Thanks
Mark
Doc, has anyone tested 6.8 on 8" grouted, reinforced concrete block walls?
I see a lot of references to "cinderblocks," which is typically ignorance on the part of the speaker since building are actually built from CMU, which is typically grouted and reinforced with rebar.
I actually saw a video that NSWC Crane made up where they fired 7.62 through a block wall. The problem was that it wasn't grouted. That means it was perhaps 25% of the thickness (added together) of a proper wall.
I believe the video was by NSWC Dahlgren, not Crane; and yes, it was a poorly done test...
I am unaware of any 6.8 mm test shots against reinforced concrete block walls--we have only done the standard FBI/IWBA type tests.
I see a lot of references to "cinderblocks," which is typically ignorance on the part of the speaker since building are actually built from CMU, which is typically grouted and reinforced with rebar.
SethB, something to consider is that some walls are simply stacked cinderblocks. Many of the construction projects I see around Iraq are not up to "code" from what you and I would expect. No reinforcement and minimal if any grouting. So although what you say is true, in some instances a wall of bricks is just that.
I guess it all depends on location.
John Hearne
09-30-08, 19:03
For example, refer to Wolberg's SDPD study comparing shots into gelatin with nearly 150 identical shots from OIS incidents.
Doc, I'm not trying to snipe but wanted to know something.
I thought the value of gelatin was that of correlation versus replication. That is rounds that performed a certain way in gelatin tended to perform well in the field. To clarify - you're saying that gelatin result replicate results from actual shootings on a 1:1 level? Also, I had read somewhere that the IWBA 4-layer denim had the best correlation with real-world shootings. Is this correct or does some other test replicate real-world performance better?
"That is rounds that performed a certain way in gelatin tended to perform well in the field."
Yes
"To clarify - you're saying that gelatin result replicate results from actual shootings on a 1:1 level?"
No I am not saying that, but in Wolberg's specific data on 9 mm 147 gr JHP OIS incidents, the results were nearly identical.
"I had read somewhere that the IWBA 4-layer denim had the best correlation with real-world shootings."
Loads that perform well in the IWBA 4-layer denim test have tended to work very well in actual shooting incidents.
Is there a listing online somewhere of the loads that did well in IWBA 4-layer test?
Yes, as has been posted several times before...see below:
The following loads all demonstrate outstanding terminal performance and can be considered acceptable for duty/self-defense use:
9 mm:
Barnes XPB 105 & 115 gr JHP (copper bullet)
Federal Tactical 124 gr JHP (LE9T1)
Speer Gold Dot 124 gr +P JHP
Winchester Ranger-T 124 gr +P JHP (RA9124TP)
Winchester Partition Gold 124 gr JHP (RA91P)
Winchester Ranger-T 127 gr +P+ JHP (RA9TA)
Federal Tactical 135 gr +P JHP (LE9T5)
Federal HST 147 gr JHP (P9HST2)
Remington Golden Saber 147 gr JHP (GS9MMC)
Speer Gold Dot 147 gr JHP
Winchester Ranger-T 147 gr JHP (RA9T)
Winchester 147 gr bonded JHP (RA9B/Q4364)
.40 S&W:
Barnes XPB 140 & 155 gr JHP (copper bullet)
Speer Gold Dot 155 gr JHP
Federal Tactical 165 gr JHP (LE40T3)
Winchester Ranger-T 165 gr JHP (RA40TA)
Winchester Partition Gold 165 gr JHP (RA401P)
Federal HST 180 gr JHP (P40HST1)
Federal Tactical 180 gr JHP (LE40T1)
Remington Golden Saber 180 gr JHP (GS40SWB)
Speer Gold Dot 180 gr JHP
Winchester Ranger-T 180 gr JHP (RA40T)
Winchester 180 gr bonded JHP (Q4355)
.45 ACP:
Barnes XPB 185 gr JHP (copper bullet)
Federal HST 230 gr JHP (P45HST2)
Federal HST 230 gr +P JHP (P45HST1)
Federal Tactical 230 gr JHP (LE45T1)
Speer Gold Dot 230 gr JHP
Winchester Ranger-T 230 gr JHP (RA45T)
Winchester Ranger-T 230 gr +P JHP (RA45TP)
Notes:
-- Obviously, clone loads using the same bullet at the same velocity work equally well (ie. Black Hills ammo using Gold Dot bullets, Corbon loads using Barnes XPB bullets, etc…)
-- Bullet designs like the Silver Tip, Hydra-Shok, and Black Talon were state of the art 10 or 15 years ago. Modern ammunition which has been designed for robust expansion against clothing and intermediate barriers is significantly superior to the older designs. The bullets in the Federal Classic and Hydrashok line are outperformed by other ATK products such as the Federal Tactical and HST, as well as the Speer Gold Dot; likewise Winchester Ranger Talons are far superior to the old Black Talons or civilian SXT's.
Thank doc. I have seen the recommended list of loads before, I think maybe it was over on Tactical Forums.
What I was specifically wondering about here is, do we have anywhere online or in a spreadsheet the info that tracks the RESULTS of how specific loads performed in the IWBA 4-layer test (i.e., Load X penetrated 12.5", Load Y penetrated 13" and broke apart, etc).
Not a big deal, but if available I'd be really interested to see how some of my favorite carry loads stack up versus others in this particular test. I had not heard this point until now, that this particular test seems to correlate well with how a round performs overall in real-world conditions.
Uh...that's why the test is done...
There is no comprehensive list of results, but most have been previously presented at TF.
SethB, something to consider is that some walls are simply stacked cinderblocks. Many of the construction projects I see around Iraq are not up to "code" from what you and I would expect. No reinforcement and minimal if any grouting. So although what you say is true, in some instances a wall of bricks is just that.
I guess it all depends on location.
I understand that, but all too often I see people talk about the capability of M80 ball, for instance, to go through a block wall. It won't. Not through eight inches of solid concrete. Especially if you've got #8 bar in every fourth cell.
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