Green Tipped 5.56 NATO Vs. 5.56 55gr

[redcon1]

Do not confuse a bullets inherent stability with its accuracy.

Stability is a measure of the behavior of the long axis of the bullet relative to the path of flight.

Accuracy is how well one path of flight matches the previous, and the next.

I think I'm looking more at terminal ballistics characteristics as a function of stability, under stability and over stability. I have shot m855 out of a 7 /1/2 " barrel. Pretty much every bullet put a perfect keyhole in the target. Even though the twist was sufficient to stabilize a SS109, the barrel was so short that there wasn't enough velocity to stabilize the bullet and they all tumbled. At the time I thought to myself, that sucks, I should shoot lighter bullets out of this pistol AR15 so the rounds will be more stable but as I thought about it more, I suspected that that tumbling bullet would be devastating terminally and would guarantee irregular wound channels and greatly increase the likelihood of fragmentation along the cannelure. A bullet entering the chest could end up coming out the abdomen or the neck and thus, would be more likely to strike vital organs and structures as it passed through. It would be more likely to break at the cannelure too and would likely create at least 2 wound channels. So with that in mind, I don't know that you would want your M855 to be overly stable. Understabilized would, IMO, be more lethal but it would certainly come at a loss of accuracy.
I once recovered an M80 ball round that had accidentally been discharged in a house (from an FN-FAL that I subsequently acquired). It went through a door, multiple walls, a bathroom vanity, both sides of a bathtub and through 20-30 classic rock albums. What was interesting was that when the bullet hit the bath tub, it broke into three separate projectiles and each of those projectiles still carried enough energy to go through the other side of the bathtub, the bathroom wall and into a closet where the albums were all lined up. The three fragments were interestingly, all located in the albums and they were not small fragments. That's what you want a military projectile to do. I shoot targets however so I want my bullets to be optimally stable, accurate and consistent from one shot to the next. I don't care what they do terminally. They only have to punch a hole through a piece of paper.

 

[DustyGmt]

He was probably shooting at 25 meters.

Probably. It does seem like pretty suspect accuracy.

 

[HowieG]

I think I'm looking more at terminal ballistics characteristics as a function of stability, under stability and over stability. I have shot m855 out of a 7 /1/2 " barrel. Pretty much every bullet put a perfect keyhole in the target. Even though the twist was sufficient to stabilize a SS109, the barrel was so short that there wasn't enough velocity to stabilize the bullet and they all tumbled. At the time I thought to myself, that sucks, I should shoot lighter bullets out of this pistol AR15 so the rounds will be more stable but as I thought about it more, I suspected that that tumbling bullet would be devastating terminally and would guarantee irregular wound channels and greatly increase the likelihood of fragmentation along the cannelure. A bullet entering the chest could end up coming out the abdomen or the neck and thus, would be more likely to strike vital organs and structures as it passed through. It would be more likely to break at the cannelure too and would likely create at least 2 wound channels. So with that in mind, I don't know that you would want your M855 to be overly stable. Understabilized would, IMO, be more lethal but it would certainly come at a loss of accuracy.
I once recovered an M80 ball round that had accidentally been discharged in a house (from an FN-FAL that I subsequently acquired). It went through a door, multiple walls, a bathroom vanity, both sides of a bathtub and through 20-30 classic rock albums. What was interesting was that when the bullet hit the bath tub, it broke into three separate projectiles and each of those projectiles still carried enough energy to go through the other side of the bathtub, the bathroom wall and into a closet where the albums were all lined up. The three fragments were interestingly, all located in the albums and they were not small fragments. That's what you want a military projectile to do. I shoot targets however so I want my bullets to be optimally stable, accurate and consistent from one shot to the next. I don't care what they do terminally. They only have to punch a hole through a piece of paper.

Yawing on impact is one thing. Yawing in flight is quite another. Interesting FAL story.

 

[redcon1]

Yawing on impact is one thing. Yawing in flight is quite another.

These were more than yawing, they were tumbling like tiny little 62 grain copper/ steel and lead buzz saws flying at ~2,200 fps and they were hitting the target surprisingly well with that 7 1/2" barrel, certainly not with rifle like accuracy but with pistol like accuracy. The tumbling effect would certainly not be conducive to accuracy or to barrier penetration but against flesh and bone, they would probably be more effective at the reduced velocity than if they were perfectly stable in flight. If they were perfectly stable in flight at the reduced velocity, you would almost certainly get nothing but the ice pick penetration. If they were tumbling all the way to the target, you would get somewhat unpredictable terminal effects but I think it's safe to say, there wouldn't be any ice pick holes.

Interesting FAL story.

The individual was playing with his new trigger crank and didn't realize he had a live round in the chamber and turned the crank and BOOM, right there in the living room. A cop lived next door but nothing was ever said and nobody came knocking on the door surprisingly. Accidental discharge of a full power .308 in your living room in the middle of the night! Can you imagine that? Oops! That FAL shoots real well for an FAL actually. It's a DSA with the Badger Barrel. Hell of a nice rifle. I'll never get rid of it. Plus it's very sentimental to me. It wasn't me that accidentally fired that gun either btw. I swear. But it is a good story that I like to tell when discussing rifle penetration which is a subject that frequently comes up on these forums because stories are fun.

 

[lysanderxiii]

These were more than yawing, they were tumbling like tiny little 62 grain copper/ steel and lead buzz saws flying at ~2,200 fps and they were hitting the target surprisingly well with that 7 1/2" barrel, certainly not with rifle like accuracy but with pistol like accuracy. The tumbling effect would certainly not be conducive to accuracy or to barrier penetration but against flesh and bone, they would probably be more effective at the reduced velocity than if they were perfectly stable in flight. If they were perfectly stable in flight at the reduced velocity, you would almost certainly get nothing but the ice pick penetration. If they were tumbling all the way to the target, you would get somewhat unpredictable terminal effects but I think it's safe to say, there wouldn't be any ice pick holes.

If you were getting pistol level accuracy, they were probably just yawing in flight.

You would be surprised how high a yaw a bullet can have.

 

[redcon1]

If you were getting pistol level accuracy, they were probably just yawing in flight.

You would be surprised how high a yaw a bullet can have.

That's possible. I never really investigated it after that. I still have the gun so I probably should because it was interesting. It's a Bushmaster Carbon 15 that I bought way back when after a prominent gun control advocate had warned us that this was the most dangerous firearm in America.
So the specs on it are a 7.25" barrel and it looks like it has a 1:10" twist. The twist rate isn't visible on the barrel from what i can see so I assume this is correct. I never chronographed anything out of it but this source claims that Bushmaster told him that SS109s averaged 2,300 fps. This source suggests that 2,200 would be expected. I split the difference and plugged the data into the Berger stability calculator using .151 G7 BC and the bullet is at the lower end of marginally stable, barely stable IOW. So, anecdotal observational analysis would suggest that the bullets were less stable than suggested by the calculator or perhaps losing stability as they shed velocity or, as you suggested, yawing wildly which would actually be desirable. According to the calculator, this bullet becomes unstable at around 1,725 fps but that is act the muzzle. It isn't entirely clear how a marginally stabilized bullet at the muzzle would behave downrange after shedding a few hundred FPS, if gyroscopic stability would be maintained, worsened or improved. Again, my anecdotal observational analysis suggests that it would not be improved or maintained at the very least but it is anecdotal evidence.

 

[HowieG]

These were more than yawing, they were tumbling like tiny little 62 grain copper/ steel and lead buzz saws flying at ~2,200 fps and they were hitting the target surprisingly well with that 7 1/2" barrel, certainly not with rifle like accuracy but with pistol like accuracy. The tumbling effect would certainly not be conducive to accuracy or to barrier penetration but against flesh and bone, they would probably be more effective at the reduced velocity than if they were perfectly stable in flight. If they were perfectly stable in flight at the reduced velocity, you would almost certainly get nothing but the ice pick penetration. If they were tumbling all the way to the target, you would get somewhat unpredictable terminal effects but I think it's safe to say, there wouldn't be any ice pick holes.

The individual was playing with his new trigger crank and didn't realize he had a live round in the chamber and turned the crank and BOOM, right there in the living room. A cop lived next door but nothing was ever said and nobody came knocking on the door surprisingly. Accidental discharge of a full power .308 in your living room in the middle of the night! Can you imagine that? Oops! That FAL shoots real well for an FAL actually. It's a DSA with the Badger Barrel. Hell of a nice rifle. I'll never get rid of it. Plus it's very sentimental to me. It wasn't me that accidentally fired that gun either btw. I swear. But it is a good story that I like to tell when discussing rifle penetration which is a subject that frequently comes up on these forums because stories are fun.
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I think if you are going to have an AD in the house, it's a good thing to use something a little less potent. Those HIPO rounds can end up killing a neighbor or your dog. Did you just do a marine epoxy patch on the tub??

 

[HowieG]

That's possible. I never really investigated it after that. I still have the gun so I probably should because it was interesting. It's a Bushmaster Carbon 15 that I bought way back when after a prominent gun control advocate had warned us that this was the most dangerous firearm in America.
So the specs on it are a 7.25" barrel and it looks like it has a 1:10" twist. The twist rate isn't visible on the barrel from what i can see so I assume this is correct. I never chronographed anything out of it but this source claims that Bushmaster told him that SS109s averaged 2,300 fps. This source suggests that 2,200 would be expected. I split the difference and plugged the data into the Berger stability calculator using .151 G7 BC and the bullet is at the lower end of marginally stable, barely stable IOW. So, anecdotal observational analysis would suggest that the bullets were less stable than suggested by the calculator or perhaps losing stability as they shed velocity or, as you suggested, yawing wildly which would actually be desirable. According to the calculator, this bullet becomes unstable at around 1,725 fps but that is act the muzzle. It isn't entirely clear how a marginally stabilized bullet at the muzzle would behave downrange after shedding a few hundred FPS, if gyroscopic stability would be maintained, worsened or improved. Again, my anecdotal observational analysis suggests that it would not be improved or maintained at the very least but it is anecdotal evidence.

You just need to move out to LEO (low earth orbit). They would stabilize fine out there.

 

[lysanderxiii]

That's possible. I never really investigated it after that. I still have the gun so I probably should because it was interesting. It's a Bushmaster Carbon 15 that I bought way back when after a prominent gun control advocate had warned us that this was the most dangerous firearm in America.
So the specs on it are a 7.25" barrel and it looks like it has a 1:10" twist. The twist rate isn't visible on the barrel from what i can see so I assume this is correct. I never chronographed anything out of it but this source claims that Bushmaster told him that SS109s averaged 2,300 fps. This source suggests that 2,200 would be expected. I split the difference and plugged the data into the Berger stability calculator using .151 G7 BC and the bullet is at the lower end of marginally stable, barely stable IOW. So, anecdotal observational analysis would suggest that the bullets were less stable than suggested by the calculator or perhaps losing stability as they shed velocity or, as you suggested, yawing wildly which would actually be desirable. According to the calculator, this bullet becomes unstable at around 1,725 fps but that is act the muzzle. It isn't entirely clear how a marginally stabilized bullet at the muzzle would behave downrange after shedding a few hundred FPS, if gyroscopic stability would be maintained, worsened or improved. Again, my anecdotal observational analysis suggests that it would not be improved or maintained at the very least but it is anecdotal evidence.

Bullets are least stable at the muzzle, after that they either calm down, continue to oscillate in pitch, or worst case tumble. As range increases, velocity decreases, and so do the aerodynamic forces caused by velocity. But the spin bleeds down so much slower than velocity.

There are two types of stability, static and dynamic stability.

Static stability is simple that if there is a yaw angle between the long axis of the bullet and the path of flight, there will be a force trying to reduce that angle. If statically unstable, the force pushed to increase the angle.

Dynamic stability means the restoring force decreases as angle decreases, or there is minimal overshoot. Dynamically unstable are just the opposite.

It is possible to have a statically stable but dynamically neutral bullets, these just maintain a constant yaw throughout the entire trajectory. M193 is such a bullet.

Now, the dynamic stability of a bullet has more to do with its aerodynamics than the spin rate.

 

[redcon1]

Bullets are least stable at the muzzle, after that they either calm down, continue to oscillate in pitch, or worst case tumble. As range increases, velocity decreases, and so do the aerodynamic forces caused by velocity. But the spin bleeds down so much slower than velocity.

If you were just at the hairy edge of unstable at the muzzle to begin with, such that the bullet wasn't tumbling but was really trying to, even though the RPM bleed off is less than velocity, the spin axis could still lose just enough rigidity to allow that marginally stable bullet to no longer be able to resist it's "desire" to tumble and then keyholes might be evident down range. Perhaps the bullets would have resisted the tumbling for long enough that accuracy would not yet be terribly affected and bullets would be minute of paper plate at 100 yards which would be acceptable for a 7 1/2" barreled AR15 IMO. This is probably a pretty ideal situation in fact as you would still get decent enough accuracy and you would get the SS109 hitting the target sideways and increasing the likelihood of fragmenting and yawing terminally.

There are two types of stability, static and dynamic stability.

I have actually read your posts here at THR from years ago about this subject. Tiborauaurus Rex has a lot of good info on this on his you tube Sniper 101 channel as well starting around episode #66 through #70.

 

[redcon1]

Did you just do a marine epoxy patch on the tub??

He did. I didn't. LOL It wasn't me, I swear.

 

[HowieG]

He did. I didn't. LOL It wasn't me, I swear.

Yeah, SURE . Whatever you say. The tub needs SAPI plates.

 

[redcon1]

Yeah, SURE . Whatever you say. The tub needs SAPI plates.

Not a bad idea and it just goes to show that there really isna good place to hide from a 7.62 NATO FMJ in a typical house. Maybe behind a bathtub and a large pile of classic rock albums. Make yourself very small.

 

[Shawn Dodson]

...The inconsistencies were related to velocity and impact angle and was called "fleet yaw".

"Fleet yaw" refers to the gun, not the bullet. Each rifle/carbine (gun) is an individual, and each gun stabilizes bullets differently. Some guns stabilize bullets very well, other don't. Which is why different soldiers reported different effects. Some soldiers had good results when shooting bad guys with M855, other soldiers didn't - even with ammo from the same lot. All were telling the truth. It was their guns that made the difference - hence "Fleet Yaw" refers to stabilization inconsistencies among the "fleet" of guns.

This ultimately led to the use of the Mk262 and Mk 318 rounds and then the development of M855A1 EPR.

The Army didn't "develop" M855A1. It literally stole the basic bullet design from Liberty Ammunition. Liberty sued and the Army was ordered to pay Liberty a royalty fee for each bullet it produced. The Army appealed and won. See - BREAKING NEWS: Liberty Ammunition LOSES M855A1 EPR Appeals Lawsuit in Federal Claims Court, US Army CLEARED -The Firearm Blog

Also - U.S. loses patent suit, owes ammo maker $15M (armytimes.com)

 

[HowieG]

Not a bad idea and it just goes to show that there really isna good place to hide from a 7.62 NATO FMJ in a typical house. Maybe behind a bathtub and a large pile of classic rock albums. Make yourself very small.

The tub to have is one of those antique cast iron and enamel claw foot tubs. I think they would be plenty resistant.

 

[HowieG]

"Fleet yaw" refers to the gun, not the bullet. Each rifle/carbine (gun) is an individual, and each gun stabilizes bullets differently. Some guns stabilize bullets very well, other don't. Which is why different soldiers reported different effects. Some soldiers had good results when shooting bad guys with M855, other soldiers didn't - even with ammo from the same lot. All were telling the truth. It was their guns that made the difference - hence "Fleet Yaw" refers to stabilization inconsistencies among the "fleet" of guns.



The Army didn't "develop" M855A1. It literally stole the basic bullet design from Liberty Ammunition. Liberty sued and the Army was ordered to pay Liberty a royalty fee for each bullet it produced. The Army appealed and won. See - BREAKING NEWS: Liberty Ammunition LOSES M855A1 EPR Appeals Lawsuit in Federal Claims Court, US Army CLEARED -The Firearm Blog

Also - U.S. loses patent suit, owes ammo maker $15M (armytimes.com)

I thought fleet yaw only applied to Navy guns.

 

[entropy]

The tub to have is one of those antique cast iron and enamel claw foot tubs. I think they would be plenty resistant.

Not so sure on that one. I once shot up a couple cast iron pots and pans with 7.62x54R. Hit on the flat, they punched big jagged holes, no pulling the metal in. When fired into curved parts, or angled flat parts, they either punched through as above, or ricocheted off, leaving a bit of jacket material on it, dependent on the angle.

 

[HowieG]

Not so sure on that one. I once shot up a couple cast iron pots and pans with 7.62x54R. Hit on the flat, they punched big jagged holes, no pulling the metal in. When fired into curved parts, or angled flat parts, they either punched through as above, or ricocheted off, leaving a bit of jacket material on it, dependent on the angle.

Well, antique claw foot tubs are a LOT thicker than pots and have sloped sides. Also, I was going by the story where the bullet in question went through a door, multiple walls, and a vanity before it hit the tub. That is a bit different from point blank. M80 ball is just 150gr FMJ. It's not armor piercing.

 

[entropy]

And, if it did punch through, it would create a larger, wider, and heavier chunk of cast iron going much slower, so yeah, it's probably a safe haven. In some neighborhoods, when the bullets start flying, they all hunker down in the bathtub.

 

[HowieG]

And, if it did punch through, it would create a larger, wider, and heavier chunk of cast iron going much slower, so yeah, it's probably a safe haven. In some neighborhoods, when the bullets start flying, they all hunker down in the bathtub.

That used to be a really good idea before fiberglass tubs.

 

[redcon1]

"Fleet yaw" refers to the gun, not the bullet. Each rifle/carbine (gun) is an individual, and each gun stabilizes bullets differently. Some guns stabilize bullets very well, other don't. Which is why different soldiers reported different effects. Some soldiers had good results when shooting bad guys with M855, other soldiers didn't - even with ammo from the same lot. All were telling the truth. It was their guns that made the difference - hence "Fleet Yaw" refers to stabilization inconsistencies among the "fleet" of guns.

I think that's what we're talking about here-what it is that would cause the green tip SS109 to yaw terminally when fired from one gun and not another. Impact angle is what determines if the bullet yaws and impact angle will be related to yaw and precession, a bullet that is overstabilized would, in theory, have a more rigid gyroscopic axis as it travelled to the target and would be less likely to hit the target at an angle that would promote yaw. My example of the SS109s keyholing from the 7 1/2" Bushmaster pistol would be an extreme example of the opposite-a bullet travelling on a less rigid gyroscopic axis which is struggling to not start tumbling over that axis and , ultimately as spin/stability decreases, it loses the struggle at some distance and begins tumbling which shows up as keyholes in the target. I have to think that such a bullet would be far more lethal than that same bullet if it hit dead on at the reduced velocity. It's a complex thing to try to figure out mathematically and might be better understood through observational analysis such as I have described as opposed to trying to overthink it. We have m855. We have a 7 1/2" 1:10" twist barrel. The ammo keyholes. This was well over a decade ago so I don't recall the distance or the percentage of keyholes. It seems like it was most of them. It seems like it was between 25 and 100 meters. It was no more than 100 meters, I know that and was probably 50-75 meters. The bullets were all on the target at this range but pretty widely dispersed but it's not like it's a target pistol.

All this talk makes me want to shoot some more of that M855 into some ballistic gel and see what a keyholing SS109 does. I'm thinking it would be impressive, more impressive than the same bullet fired and well stabilized at the same diminished velocity but with a tighter twist.

 

[HowieG]

I think that's what we're talking about here-what it is that would cause the green tip SS109 to yaw terminally when fired from one gun and not another. Impact angle is what determines if the bullet yaws and impact angle will be related to yaw and precession, a bullet that is overstabilized would, in theory, have a more rigid gyroscopic axis as it travelled to the target and would be less likely to hit the target at an angle that would promote yaw. My example of the SS109s keyholing from the 7 1/2" Bushmaster pistol would be an extreme example of the opposite-a bullet travelling on a less rigid gyroscopic axis which is struggling to not start tumbling over that axis and , ultimately as spin/stability decreases, it loses the struggle at some distance and begins tumbling which shows up as keyholes in the target. I have to think that such a bullet would be far more lethal than that same bullet if it hit dead on at the reduced velocity. It's a complex thing to try to figure out mathematically and might be better understood through observational analysis such as I have described as opposed to trying to overthink it. We have m855. We have a 7 1/2" 1:10" twist barrel. The ammo keyholes. This was well over a decade ago so I don't recall the distance or the percentage of keyholes. It seems like it was most of them. It seems like it was between 25 and 100 meters. It was no more than 100 meters, I know that and was probably 50-75 meters. The bullets were all on the target at this range but pretty widely dispersed but it's not like it's a target pistol.

All this talk makes me want to shoot some more of that M855 into some ballistic gel and see what a keyholing SS109 does. I'm thinking it would be impressive, more impressive than the same bullet fired and well stabilized at the same diminished velocity but with a tighter twist.

Why use 855A1 for that. You could load up experimental loads using a too heavy cheap bullet that you know won't stabilize, like a 69 grainer. Then shoot them out of that short barrel into BG. I would expect not much penetration at any kind of distance except short. Surface effects would not be pretty though.

Frankly, I never understood the concept of a pistol AR. Doesn't make sense to me. Carry a carbine and strap a handgun to your hip and be done with it.

 

[redcon1]

Why use 855A1 for that. You could load up experimental loads using a too heavy cheap bullet that you know won't stabilize, like a 69 grainer. Then shoot them out of that short barrel into BG. I would expect not much penetration at any kind of distance except short. Surface effects would not be pretty though.

Frankly, I never understood the concept of a pistol AR. Doesn't make sense to me. Carry a carbine and strap a handgun to your hip and be done with it.

I have thousands of SS109s that I have acquired over the years. Those top 3 bags are all SS109s. The other bags are just random .308 FMJs. I know lots of other people that have just as many and more. I never did much with them as I shoot mostly 7.62x51 but I always wanted to experiment with them and since I have so many of them, I'm kind of curious about them. Are they crap or not? Now that the M855A1 is all the rage, I'm even more curious about them.

I bought the AR pistol because, way back when, Michael Bloomberg stood in front of the cameras and held one of them up and proclaimed it to be the most dangerous weapon in America or something to that effect so I had to have one. I do think the PDW is a legitimate concept and maybe the 5.56x45 isn't the ideal caliber for a PDW but, in my reality, it probably is actually. If these projectiles are accurate to a hundred yards but then tumbling by the time they reach 100 yards and, better yet, breaking apart due to keyholing, that's something worth verifying I think.

 

[HowieG]

Well, if you have stacks of free ammo, that trumps anything else.

What do you think the impact velocity would be? I don't know how I would measure that. Couldn't use a ballistics program on a keyholing bullet. I guess Labradar would be the best way. I would bet they are pretty slow at 100.

I think 5.7x28mm is a much better PDW cartridge. More in tune with a short barrel and fairly effective against armor. At least it used to be. I just watched a test fire against the Enhanced Combat Helmet. The one made out of UHMWPE. It's rated for 7.62x39mm at 100, but the test guys tried out 7.62 Nato ball and it didn't penetrate. I am real impressed with UHMWPE.

 

[Shawn Dodson]

Frankly, I never understood the concept of a pistol AR. Doesn't make sense to me. Carry a carbine and strap a handgun to your hip and be done with it.

An AR "pistol" fitted with an arm brace allows one to circumvent the ATF to have a lawful short barreled rifle. A CCW license allows it to be carried loaded inside a vehicle in many states, plus it can be carried interstate without the need for ATF's permission.