Comments by "Titanium Rain" (@ChucksSEADnDEAD) on "Meet the three 6.8mm bids competing to replace the M-16" video.

@MCWordicus the problem is that if you go with a 6.8 limited to the dimensions of an AR-15 magwell, it sucks. You'll gain a little ammo weight and greater recoil impulse for no benefit at all. The trajectory is worse, the bullet being slower (because it's heavier) makes it less capable against armor and less likely to tumble (the US military spent a pretty penny making sure M855A1 tumbles). If you want a hunting AR in a state that doesn't allow 5.56 then 6.8 is great. If you're in a military trying to shoot at people 5.56 is better than 6.8 constrained to the AR magwell. You need to change the weapon and give the caliber a longer casing to make sure it goes fast.
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@chef7734 "The 6.8 spc has as much energy at 250 meters as the m855 has at the muzzle" - not true. M885 at the muzzle from a 14.5" is roughly 1600 J. A 110gr 6.8 SPC will have around 1300-1400 J at 200 meters. I don't see the energy climbing another 200 joule in the next 50 meters. "You gain 40 to 50% kenetic energy at 300 meters and in and 35%greater out to 600 meters" - energy isn't everything. You need to put that energy into tissue. We know that with two bullets travelling at the same velocity, the lighter one tumbles better. We all know that with two bullets with the same mass, the faster one tumbles better. 5.56 is both faster (by about 100 ft/s) at 300 meters and lighter. More energy on a round that is more likely to icepick through and not put that energy on tissue means very little. Remember, you're gonna be using FMJ rounds which depend on the tumbling to transfer energy, not hollow points. With hollow points, by all means pick 6.8 SPC. If the round weighs more, you're carrying less for the same weight. If the recoil is higher and bullet slower, marksmanship goes down because it becomes harder to guesstimate bullet travel time and bullet drop at unknown distances and once you pull the trigger you're gonna be slower to line up a second shot. You're gonna be carrying less firepower into battle, you're gonna be more likely to miss, and even if you hit you're less likely to actually put the target down. I think you're getting a bad deal with 6.8 SPC because of sheer physics alone. You can simply carry the same amount of ammo and add a bunch of weight to the rifle to bring recoil to 5.56 levels, but you're punishing your back for a caliber that's not going to do much for you and is gonna have worse trajectory anyway. "You have a larger round that has more powder pushing it in the same magwell as the 5.56." - the larger bullet also takes up more case space. If I go by Nosler load data a 223 Rem case (for some reason 5.56 NATO doesn't have 62gr load data on their website) loaded with a 62gr bullet has a 27.6 gr H2O capacity. A 6.8 SPC loaded with a 110gr bullet has a 27.5 gr H2O capacity. Again through Nosler's website a 69gr loaded in a 5.56 case has 27.5 gr H2O capacity so I rest my case, the round itself is indeed larger but because you need to stick a bigger bullet in it and still respect the OAL of the AR's magwell and magazine dimensions... you're gonna have to push the bullet deeper into the case and lose powder capacity. If you want more powder, you need either a lighter bullet (which is also shorter which gives it lower ballistic efficiency - an 85gr will have around 1040 J at 200 yards versus 5.56 62gr's 990 J - you're virtually negating the energy difference at this point) or neck it down. You're either back to 5.56 territory or trying to recreate 6mm SAW.
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@chef7734 "The 6.8 mm generates around 2,385 J (1,759 ft⋅lbf) of muzzle energy" - gonna need source for that, big guy. Barrel length, how compressed is that load, etc. "terminal ballistic advantage over the 5.56 mm of 588 J (434 ft⋅lbf)" - again, the bigger and slower bullet cannot effectively translate that energy into tissue. There's a reason why M67 and 5.45x39 7N6 exist - even the Eastern Bloc realized that 7.62x39 M43 made icepick wounds. M67 puts a rear weight bias on the bullet, 5.45 was designed to tumble from the get go. "You dont carry less just because it is slightly heavier. It doesnt work like that in real life. You just suck it up and drive on." - that's a massive misunderstanding of what weight means at the logistical level. Not only are you dragging a huge logistical chain around you where the ounces add up to tons, if we had the "suck it up" attitude about everything you'd be carrying more water, more batteries, more radios, more everything. The lighter infantry is the more effective it is. I don't remember the example right now but there's a famous story in Vietnam of two simultaneous battles for two hills, in one the Americans marched to the hill with their packs on and another simply left their packs on their exfil route and climbed the hill with only their battle rattle. The guys who carried the packs got murked and the guys with only the battle rattle repelled the attacks easily because they weren't exhausted. "We as soldiers improvise adapt and overcome" - but American doctrine is slow to change. As soon as the US changes to a heavier cartridge to defeat the armor the Russians are bragging about, they'll probably quickly authorize their soldiers to switch the plates for lighter ones so they can gain mobility. "You train to the differences in ballistics. It's not that hard." - it is hard compared to an "easy" caliber. "You mention tumbling. The 5.56 is such a small round it has to tumble to cause as much damage as a 6.8" - all rifle rounds have to tumble. Even 7.62 NATO tumbles. It doesn't tumble as early as 5.56 but it does and it rips a lot of tissue. Meanwhile 7.62x39 is the same diameter - actually .311-.312 compared to .308 - but it doesn't tumble worth a shit so coroner reports literally describe 7.62x39 wounds as very similar to pistol wounds. There's a reason why when .303 was forced to use a full metal jacket round-nose soldiers complained about the round being garbage, and when the nose of the bullet was replaced by a spitzer point with a cavity filled by wood pulp, paper or aluminum to increase tumbling the .303 gained respectable lethality. "We had issues in Afghanistan with the 5.56 m855 not being as effective as we needed." - because M855 suffers from fleet yaw issues. If it hits at 3 degrees of AoA is goes off like a hand grenade inside the body, if it hits at 0 degrees AoA it icepicks through. M855A1 was improved in the sense that it will tumble independently of fleet yaw. "Look at the ballistics during hog hunts or deer and it shows the 6.8 far more effective than the 5.56" - first, how many of those are with hollow points? Second, a shot through a hog doesn't represent a human torso. Again, a 7.62x39 M43 is a very poor wounder against humans because it exits the human torso before it starts to tumble against the resistance offered by the tissue. A large hog with a thick skin gives larger calibers better resistance for them to tumble INSIDE the animal in a way you won't see in humans.
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Mighty Fist Of Zeon! "There's a reason so many nations have switched to entirely new bullpup designs" - and half of those nations are returning to conventional rifles.
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Caseless ammo has no case to reject waste heat from the firing since the entire "case is consumed during the deflagration. However, when comparing brass/steel to plastic the metallic cartridges act as a heat conductor to the chamber while plastic acts as an insulator.
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Mighty Fist Of Zeon! How so? The Brits got an AR-10 for DMR, the New Zealanders got an AR-15 made by LMT to be their main service rifle and the French replaced the FAMAS for a HK416 aka a piston AR. For something outdated, it's still selling like hotcakes.
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@yfelwulf "35,000 plus US dead in Vietnam agree 7.62x39 works. " - not really, because so many shot by 7.62x39 lived. In fact, in the 1989 Stockton shooting Patrick Purdy fired 106 rounds from his AK into schoolchildren and killed 5 while wounding 30. The medical examination of the wounds confirmed that the rifle bullets did damage similar to handgun rounds and that explained it's lack of lethality, even against children. There's a reason the Russians switched to 5.45 and made it more lethal than 7.62.
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@ChuckBeefOG "The only reason it is utilized is price" - not really. Pretty much every lesson learned after big conflicts is that firepower wins battles and carrying lighter ammo not only increases the amount you can carry, it also increases marksmanship. When the Air Force was testing the AR15 they found that the percentage of people who qualified Expert went through the roof compared to the M14. The fact that it's cheaper is only the cherry on top.
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@0zone247 because the old one doesn't meet the criteria. It was made to fit the AR magwell, which limits performance. The new one isn't constrained by the AR magwell so you can give it more case behind the bullet, make it faster.
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J I mean, within the context of terminal ballistics I didn't think I need to mention that. No, I didn't mean it in the sense of bullets tumbling in the air.
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@abc4781 Except that 6.8 SPC doesn't meet the criteria. You can't fit the bullet they want and make it go at the speed they want from the limits of the AR magwell.
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@greggreed3840 "the 6.8 SPCll vastly out performs the 5.56 in penetration" - What? How so? Which loading, which bullet, which target are we talking about? "trajectory is the same as the .308." - Not really. "With the 6.8 SPCll you're pushing a .277 110gr bullet at 2800 fps. I think you need to go study some physics." - Not really, out of a 16 inch barrel you get 2500-2560 fps with a 110gr. "If you want less recoil then drop to a 90 gr pill at over 3200fps." - not even an 85gr will get you that. And by the time you drop to 85gr you gave up so much sectional density your ballistic efficiency takes a hit. "As far as tumbling for the 5.56 that went away when they went to heavier bullets and faster twist rates" - that's not true. Modern 5.56 is made to tumble: https://www.youtube.com/watch?v=DBdVGJT5ezY "The reason Stoner went with the 1-12 twist" - the reason Stoner went with the 1/14 twist was because at the time the available barrel blanks for the .224 bullet were rifled with twists for very light varmint-hunting rounds. It's obvious with the historical context in mind, .224 was used to hunt critters and not to be used with heavy-for-caliber bullets meant for military service, so nobody made barrel blanks meant for heavier bullets. "was to achieve the destabilization of the bullet so it would tumble on impact" - That's false. All spitzer pointed bullets with some form or rear weight bias will tumble, eventually. If given a large enough target, even 7.62x39mm M43 ball will tumble (it just so happens that against human targets it tumbles after it already went through the person). 7.62 NATO tumbles. The rifling twist of a firearm CANNOT stabilize bullets in tissue. The twist rate would have to be so fast it would look like threading. "Faster twist, heavier bullet no tumble." - That's not true. M855 still tumbles and frags like crazy - but it depends on the angle of attack of the bullet at the moment of impact. M855A1 was made so that it can tumble and fragment independently of the angle at which it hits. Again, another video on the modern 62gr M855A1 tumbling and fragmenting: https://www.youtube.com/watch?v=clZwnSQnfH8
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@alinmeleandra3175 "There is the option to change to powder content inside the casing. You can obtain the same virtual kinetic energy for a heavier bullet in a "smaller" casing, by increasing the effectiveness of the powder itself" - No such thing as a free lunch. Trying to overpressure ammunition just to keep the lower makes no fucking sense. "As far as I know, the M4 direct impingement system loses a lot of gas in order to re-cycle the bolt" - that's almost negligible. Most of the powder has burned by the time the bullet crosses the gas block (unless you're running a sbr) and pressure leakage is constrained by the diameter of the gas port. Switching the 14.5" for 16" barrels would probably yield more feet per second than changing the gas system. "On the other hand, a bigger caliber bullet (not sure if 6.8 has this advantage) , does not really need to transfer all its energy to a target "to drop it"." - I'm sorry but that extra 0,053" of bullet diameter doesn't matter much. You either clip the central nervous system or your don't. If you don't score a CNS hit, you either hit the heart or you don't. And then it's the rest of the vitals and finally the remaining non-vital tissue. If you're not hitting somewhere that will instantly remove a person's ability to fight, you depend on the damage done to the organs and tissue to make a stoppage. This doesn't depend as much on caliber as one would think. The speed of the round, how early it upsets in tissue, if it fragments or not, etc are very important. "I am quite sure you do not want to be hit by an AK round" - I don't want to be hit by ANY round. But gun to the head, I have no choice but to get shot, I'd rather take a M43 7.62x39mm than a 5.56 M193 or M855A1. The M43 is known for making pass-through wounds that look like pistol wounds to coroners. M193 and M855A1 will tumble, come apart and turn tissue into shreds. "A bigger bullet, creates a bigger hole," - again, we're talking about a 0,053 inch difference between 6.8 and 5.56. Less than one eighteenth of an inch. "also cavity it leave behind it, tends to be bigger" - https://www.youtube.com/watch?v=-u5Uk0ae4p4 this is the cavity from a non-fragmenting 5.56 round impacting 20% ballistics get at 2800 fps. It damned near split the gelatin block in two. Now, I am sure you can get a 6.8 to tumble. The only thing I'm saying is, 5.56 is both faster and lighter which allows for a faster upset of the projectile when it impacts tissue. And it's lighter, has better trajectory, etc so the benefits for using 5.56 outshine the very moderate improvement in ballistic performance.
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@samuelmorales2344 "The AR is a longer range automatic rifle" - people using M4s as automatic rifles proved to be a disaster. "while the M16 will get the 6.8mm" - on the first sentence of your post you said the 6.8mm is necessary to enhance penetration against body armor. If you stick 6.8mm on an AR you don't get a good armor penetrator because of the lower velocity. You're constrained by the magwell dimensions. The M193 flew off the muzzle of a 20 inch barrel at something like 3200 fps. If you're gonna carry a 20" musket might as well NOT use a M16 as the base and bring in an AR-10 design with the 6.8 AP bullet and make it fly at crazy speeds instead of being limited by the magwell. "Tumbling rounds or fragmenting rounds do not work against body armor." - that's false. ALL spitzer pointed bullets tumble, it's just a matter of how soon.
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@billy56081 I believe you. How compressed is that loading, though? I'm looking at load data right now and to get 2800-2900 fps out of a 20 inch barrel you need compressed loads. And assuming you're only losing 50-150 fps by chopping down 7.5 inches of barrel... You still need to deal with the fact that the gold dot is a lead core bullet that's going to have to be replaced by an EPR design that is low in metal toxicity so that it can be fired in American ranges without being closed due to environmental regulations and also take into account the longer tracer projectiles. You're starting off from a near max charge according to load data, compressing the fuck out of the powder and then sticking an elongated bullet in that case? If anyone fucks up at the factory - remember, the first M855A1 batches were overpressured as well - that case is a hand grenade.
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@donovanb4739 weird question, because ping pong balls weigh grams while each train carriage can weigh-in at 20-30 tons. A better comparison would be a 14 pound bowling ball versus a 10 pound bowling ball.
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@billy56081 that's the problem. It's like saying you can get 500hp out of Car XYZ by telling me I can go to the XYZ forums. Of course that enthusiasts can fine tune performance out of something that doesn't have it from factory. The military will be using factory ammo, not some tinkerer's home loads.
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@billy56081 what part of military rounds requiring the ability to load LONGER bullets in them to make up for steel core or tracer rounds didn't you get?
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@billy56081 like I said, what happens to the internal volume of a case when you load a longer bullet? You're deflecting because you know I'm right. Grow the fuck up.
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@flabySPARTAN228 I know, I'm just replying to the people talking about doing a caliber conversion on existing rifles.
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@smith8399 To be fair there's nothing wrong with a 6.8 AR, especially for those who can't hunt with 5.56. But as a service caliber, there's no advantage on slapping a larger caliber into a 5.56 weapon. It's preferable to change rifle and caliber at the same time than half-assing.
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@Laotzu.Goldbug the caveat being that there's anything from rifle to pistol and even black powder bullets around the .5 inch mark. The reason why people talk about "6.5 and 6.8 mm bullets" is because of the selection of high performing rifle bullets.
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@PugilistCactus "5.57 isn't any good against the nations we will be fighting soon." - but why?
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@ostiariusalpha I still think this is a fool's errand. If you make individual armor plates irrelevant by creating a round that punches through them... are we to expect the enemy to keep wearing them in the interest of fairness or something?
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@ostiariusalpha "but if you can keep your enemy from using composite armor in the first place, you're already ahead of the game" - But that's the problem. The enemy simply being able to ditch their plates is actually beneficial to them because they'll either be able to carry more firepower for the same weight, or carry the same firepower with the added mobility. On the other hand, using a caliber that can be stopped by the enemy armor forces them to use their Gucci plates - which will punish their shoulders, backs and knees. "That keeps them vulnerable to all those M4 carbines you still have in inventory." - the problem is that American doctrine is too slow to change. It's gonna take what, 5-6 years for the generals to approve the reissuing of 5.56 weapons to infantry units? The enemy will not give a fuck and stop wearing the plates day one.
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@ostiariusalpha How is it a death sentence? If American projectiles go through the plate, you're in severe risk of getting killed whether you're wearing it or not. Not wearing it increases your chances of survival because you have better mobility, and all your comrades are also fighting with less fatigue on their bodies. I wouldn't wear it if I'm gonna get it in the chest. I'd rather get a shot straight through than have all the shards of plate sucked into my lungs by a smashed up bullet. "And reissuing is very rapid actually, we busted out the M14s in the arsenal in a matter of weeks" - mind that issuing "some" M14's is not the same as reversing the 5.56-to-6.8 process. The better analogy is how much time it took for the US to finally adopt armor that fits the GWOT, and replace the armor designed to keep you alive against 24/7 showering of Russian/Chinese artillery and close air support.
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Because it makes no sense to use heavy and slow rounds when you need to hit people running full sprint into cover from 300-500 meters away.
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Because 6.8 constrained by the AR lower receiver size is too slow. They want a larger cartridge to drive the bullet fast enough.
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There's countries that are only now switching from 7.62 to 5.56. They're not gonna change again any time soon.
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Because 6.8 SPC is not an improvement. Putting a bigger bullet without increasing the cartridge length means more lower muzzle velocity and more drop. Makes it harder to hit in combat, makes the bullet less effective against armor and also makes it less likely to tumble inside tissue.
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@SpaceDebris15 Increase in pressure without redesigning the locking lugs will lead to shorter bolt life. "there is onlt a 2mm different in case length" - the bullet is also required to be seated deeper to retain OAL. Remember, the Army will probably stick with the EPR design so you have to replace a good chunk of material from the bullet with steel. This makes the bullet even longer than commercially available bullets because of the steel's lower density. You lose even more case volume. "when using the 85 gr projectile you have the same velocity as the 5.56" - 85gr in 6.8 has low sectional density. You'd be increasing the weight of the round for a very marginal increase in energy at range, essentially making 5.56 objectively better. "it would be easier logistically and financially to choose a already existing round. " - it really isn't. "It exists" doesn't automatically make it viable in terms of logistics or finances. The military has so much power to drive economies of scale that it can order a totally new caliber and it's viable because they drive so much demand for product that the industry will meet it with supply. It doesn't make sense to compromise when you have the freedom to specify exactly what you want and not be constrained by commercial offerings.
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Not really. 5.56 is cheap because of the economics of scale. If you remove the military demand for 5.56, production plants will shift to the new caliber.
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