12 ms·

One of the interesting things is that the US has effectively re-invented the 7.62x39 round (at a much higher per round cost) with same weight bullet and nearly

One of the interesting things is that the US has effectively re-invented the 7.62x39 round (at a much higher per round cost) with same weight bullet and nearly same length, which is the .300 Blackout supersonic. It's designed to work in a standard NATO 556 magazine, receiver and bolt carrier, the cartridge body is the same as a 556 NATO, it's necked to take a 7.62 bullet. https://thebiggamehuntingblog.com/300-blackout-vs-7-62x39/ https://thebiggamehuntingblog.com/300-blackout-vs-7-62x39/

halffaday 4y ago
Blackouts were an attempt to get enough thump in a room-clearing range where 5.56mm is a little lacking. Long-term, 6.8mm seems to be the direction small arms are going: https://www.armytimes.com/news/your-army/2022/04/19/army-chooses-sig-sauer-to-build-its-next-generation-squad-weapon/ https://www.armytimes.com/news/your-army/2022/04/19/army-cho...
- walrus01 4y ago
  yes it was clearly designed for short range engagements - not exactly same application as 7.62x39 as a general purpose medium range infantry cartridge. the military/contractor folks I know wouldn't even think of using blackout at ranges where anything above 250 yards would be anticipated. the blackout is also unique in that the subsonic version of it was designed from the start to be NATO-rifle-platform compatibile with a suppressor. and due to even lower velocity, even shorter range (definitely 75 yard and less). also fairly unsure on its performance vs. modern plate based body armor vs greater velocity of regular 556 nato, 6.8 as you mention, etc.
- 2OEH8eoCRo0 4y ago
  Those new 6.8mm rounds are crazy. For context, your typical rifle chamber pressure is ~60,000 psi (5.56mm, .338 lapua mag, etc) and these 6.8mm rounds go to ~80,000 psi. Punches above it's weight. Very interested in this space lately.
  - thedrbrian 4y ago
    interesting videos for the layman by Ian McCollum of Forgotten Weapons https://www.youtube.com/watch?v=MTZRCEh1Czg https://www.youtube.com/watch?v=MTZRCEh1Czg and https://www.youtube.com/watch?v=f4gst0QoMw4 https://www.youtube.com/watch?v=f4gst0QoMw4
    - 2OEH8eoCRo0 4y ago
      Thanks for sharing. I love Gun Jesus
alberth 4y ago
Dumb question: how does a 762 ballistic fit in a 556 barrel?
- icegreentea2 4y ago
  It doesn't. 300 blackout requires a new barrel. It's 'trick' is that all of the other components don't need to change.
- cbmcgee 4y ago
  It requires a different barrel. As mentioned, lower receiver, bolt carrier, magazines can be reused.
- rolph 4y ago
  PLEASE look here regarding safety issues: https://news.ycombinator.com/item?id=32389075 https://news.ycombinator.com/item?id=32389075 it doesnt fit the bore of the barrel, it 'fits' the chamber. if you are using .300 blackout and .223/5.56 nato be very carefull or do something like colour your rounds with a sharpie [edit] by the way there are very few dumb questions, asking a question is far more intelligent than acting like you know it and blundering through it by luck.
  - walrus01 4y ago
    for your average hobbyist who doesn't actually have to worry about camouflage of anything, do something like wrap bright orange hockey grip tape around any magazine body that contains .300 blackout. And some totally other color on 556.
    - rolph 4y ago
      exactly that sort of thinking. there is a color coding system for ammunition: https://www.bulletpicker.com/pdf/MIL-STD-709C.pdf https://www.bulletpicker.com/pdf/MIL-STD-709C.pdf [PDF] indicating special function, such as armor piercing; incindiary; fragmentary HE etc. it is also a popular option to have receivers colorized or stamped. alot of magazines are polymer and could easily be colorized, and detailed, for instance with a large pictogram of the intended ammunition. this is also on a little more of an angle, a reason to not let that combination of, persons you dont trust; .300 blk; and 5.56 chambers to occur.
rolph 4y ago
PSA for anyone who doesnt know this, A .300 blackout, will 'fit' into a .223; or 5.56 NATO chamber, AND allow the bolt to go into battery position. cataclysm results: https://www.thefirearmblog.com/blog/2018/06/19/lfd-research-films-the-firing-of-300-blackout-in-a-223-5-56-chamber/ https://www.thefirearmblog.com/blog/2018/06/19/lfd-research-... https://rifleshooter.com/2019/06/kaboom-300-blk-in-5-56-223-ar-15/ https://rifleshooter.com/2019/06/kaboom-300-blk-in-5-56-223-... https://www.youtube.com/watch?v=RbfIkaNlECo https://www.youtube.com/watch?v=RbfIkaNlECo
- 1_bad_plf 4y ago
  Is 7.62x39 a problem here too?
  - rolph 4y ago
    no it wont even chamber, however there is a further nuance. most current AR chambers are .223 / 5.56 WYLDE chamber meaning both will fit and function. the problem comes from a straight up old school .223 being fed 5.56. the evolved gas pressure is higher for the 5.56 round, and will probably work for a while, will put extreme use on the rifle and will eventually malfunction probably with similar results to the .300BLK problem. a 5.56 can be forced to chamber in a 7.62 chamber, but is about 6mm too long so you will know theres a problem 7.62 nato of standard configuration wont fit the lede [ogive] of the 5.56 chamber unless you shove really hard with a mallet. what you may see is a lower receiver stamped for 5.56 NATO assambled with a 7.62 upper and barrel. this is proably fine for most aluminum lowers but i would stay clear of the polymer lowers or the skeletonized milled out lowers, for the 7.62
    - walrus01 4y ago
      > what you may see is a lower receiver stamped for 5.56 NATO assambled with a 7.62 upper and barrel the last paragraph is not exactly correct, a lower receiver for 556 NATO STANAG magazines has a different length magazine well (AR-15 derived design, not AR-10) and cannot take the dimensions of an AR10 magazine/7.62 NATO magazine. you can mistakenly chamber a .300 blackout in a 556 nato rifle upper because the blackout is the same length cartridge as a 556 nato round and will feed. you cannot mistakenly shove a 7.62x51 NATO/.308 winchester round into a rifle lower/upper that is not an AR-10 derived design because there would be no way to even seat the magazine. even if you were to somehow mistakenly mount an ar10/762 NATO upper and barrel on an ar15 lower the only way you could try to get a round into the chamber would be to shove it in sideways through the ejection port
650REDHAIR 4y ago
300bo was done by AAC on its own though. There were some in the SOF community that were looking for better subsonic/more knockdown. I think 300bo is closer to 9x39mm in application.
topspin 4y ago
Blackout is limited to spec-ops use. More interesting is this: In April 2022 the DOD awarded substantial contracts[1] to Sig Sauer for the manufacture of the XM5 rifle and XM250 automatic rifle and the "6.8 Common Cartridge" as part of the Next Generation Squad Weapon Program. The new 6.8 is a much heavier and higher pressure round than the 556 and delivers far greater range and body armor defeat capability. The pressure is so great (80,000 psi, 551.6 MPa) that the case head (the 'back' part where firing pin hits) is made of stainless steel instead of brass; a 'composite' (steal + brass) case. I don't think that has ever been done in a military infantry weapon; all steel cases have been around a long time, but those are about cost saving as opposed to performance. 80,000 psi is pretty extreme in a rifle round. The high end of traditional brass case ammunition is 65,000 psi. That includes high performance rifle calibers like 338 Lapua Magnum and 22-250. Also, the XM157 Fire Control optic being built for these new rifles is remarkable: "variable magnification optic (1X8), backup etched reticle, laser rangefinder, ballistic calculator, atmospheric sensor suite, compass, Intra-Soldier Wireless, visible and infrared aiming lasers, and a digital display overlay." Due to the undoubtedly high cost these weapons will be limited to the 'first responder' combat forces and M4/M249 will be the mainstay for the rest for many years yet. But this commitment including the official designation of a new cartridge is a clear signal that the DOD is taking infantry weapon performance rather seriously. [1] https://www.army.mil/article/255827/army_awards_next_generation_squad_weapon_contract https://www.army.mil/article/255827/army_awards_next_generat... "The XM5 Rifle will replace the M4/M4A1 carbine within the close combat force, and the XM250 Automatic Rifle is the planned replacement for the M249 Squad Automatic Weapon"
- walrus01 4y ago
  > 80,000 psi is pretty extreme in a rifle round. The high end of traditional brass case ammunition is 65,000 psi. It is pretty extreme but I can't say I'm exactly surprised, metallurgy has clearly advanced quite a bit since the days when 556 NATO pressures in chamber were standardized 50+ years ago. If you have DoD budget levels of money to spend on a barrel you can clearly do higher. Barrels that meet 556 NATO spec are as cheap per unit as $100, a really nice one is $300. If it's not a problem that your barrel alone might cost $700 I can see this being totally possible.
- 4y ago
R0b0t1 4y ago
You've got it backwards, pretty much all cartridges were developed off of cartridges originally available to US hunters.

halffaday 4y ago

Blackouts were an attempt to get enough thump in a room-clearing range where 5.56mm is a little lacking. Long-term, 6.8mm seems to be the direction small arms are going: https://www.armytimes.com/news/your-army/2022/04/19/army-chooses-sig-sauer-to-build-its-next-generation-squad-weapon/ https://www.armytimes.com/news/your-army/2022/04/19/army-cho...

walrus01 4y ago
yes it was clearly designed for short range engagements - not exactly same application as 7.62x39 as a general purpose medium range infantry cartridge. the military/contractor folks I know wouldn't even think of using blackout at ranges where anything above 250 yards would be anticipated. the blackout is also unique in that the subsonic version of it was designed from the start to be NATO-rifle-platform compatibile with a suppressor. and due to even lower velocity, even shorter range (definitely 75 yard and less). also fairly unsure on its performance vs. modern plate based body armor vs greater velocity of regular 556 nato, 6.8 as you mention, etc.
2OEH8eoCRo0 4y ago
Those new 6.8mm rounds are crazy. For context, your typical rifle chamber pressure is ~60,000 psi (5.56mm, .338 lapua mag, etc) and these 6.8mm rounds go to ~80,000 psi. Punches above it's weight. Very interested in this space lately.
- thedrbrian 4y ago
  interesting videos for the layman by Ian McCollum of Forgotten Weapons https://www.youtube.com/watch?v=MTZRCEh1Czg https://www.youtube.com/watch?v=MTZRCEh1Czg and https://www.youtube.com/watch?v=f4gst0QoMw4 https://www.youtube.com/watch?v=f4gst0QoMw4
  - 2OEH8eoCRo0 4y ago
    Thanks for sharing. I love Gun Jesus

alberth 4y ago

Dumb question: how does a 762 ballistic fit in a 556 barrel?

icegreentea2 4y ago
It doesn't. 300 blackout requires a new barrel. It's 'trick' is that all of the other components don't need to change.
cbmcgee 4y ago
It requires a different barrel. As mentioned, lower receiver, bolt carrier, magazines can be reused.
rolph 4y ago
PLEASE look here regarding safety issues: https://news.ycombinator.com/item?id=32389075 https://news.ycombinator.com/item?id=32389075 it doesnt fit the bore of the barrel, it 'fits' the chamber. if you are using .300 blackout and .223/5.56 nato be very carefull or do something like colour your rounds with a sharpie [edit] by the way there are very few dumb questions, asking a question is far more intelligent than acting like you know it and blundering through it by luck.
- walrus01 4y ago
  for your average hobbyist who doesn't actually have to worry about camouflage of anything, do something like wrap bright orange hockey grip tape around any magazine body that contains .300 blackout. And some totally other color on 556.
  - rolph 4y ago
    exactly that sort of thinking. there is a color coding system for ammunition: https://www.bulletpicker.com/pdf/MIL-STD-709C.pdf https://www.bulletpicker.com/pdf/MIL-STD-709C.pdf [PDF] indicating special function, such as armor piercing; incindiary; fragmentary HE etc. it is also a popular option to have receivers colorized or stamped. alot of magazines are polymer and could easily be colorized, and detailed, for instance with a large pictogram of the intended ammunition. this is also on a little more of an angle, a reason to not let that combination of, persons you dont trust; .300 blk; and 5.56 chambers to occur.

rolph 4y ago

PSA for anyone who doesnt know this, A .300 blackout, will 'fit' into a .223; or 5.56 NATO chamber, AND allow the bolt to go into battery position. cataclysm results: https://www.thefirearmblog.com/blog/2018/06/19/lfd-research-films-the-firing-of-300-blackout-in-a-223-5-56-chamber/ https://www.thefirearmblog.com/blog/2018/06/19/lfd-research-... https://rifleshooter.com/2019/06/kaboom-300-blk-in-5-56-223-ar-15/ https://rifleshooter.com/2019/06/kaboom-300-blk-in-5-56-223-... https://www.youtube.com/watch?v=RbfIkaNlECo https://www.youtube.com/watch?v=RbfIkaNlECo

1_bad_plf 4y ago
Is 7.62x39 a problem here too?
- rolph 4y ago
  no it wont even chamber, however there is a further nuance. most current AR chambers are .223 / 5.56 WYLDE chamber meaning both will fit and function. the problem comes from a straight up old school .223 being fed 5.56. the evolved gas pressure is higher for the 5.56 round, and will probably work for a while, will put extreme use on the rifle and will eventually malfunction probably with similar results to the .300BLK problem. a 5.56 can be forced to chamber in a 7.62 chamber, but is about 6mm too long so you will know theres a problem 7.62 nato of standard configuration wont fit the lede [ogive] of the 5.56 chamber unless you shove really hard with a mallet. what you may see is a lower receiver stamped for 5.56 NATO assambled with a 7.62 upper and barrel. this is proably fine for most aluminum lowers but i would stay clear of the polymer lowers or the skeletonized milled out lowers, for the 7.62
  - walrus01 4y ago
    > what you may see is a lower receiver stamped for 5.56 NATO assambled with a 7.62 upper and barrel the last paragraph is not exactly correct, a lower receiver for 556 NATO STANAG magazines has a different length magazine well (AR-15 derived design, not AR-10) and cannot take the dimensions of an AR10 magazine/7.62 NATO magazine. you can mistakenly chamber a .300 blackout in a 556 nato rifle upper because the blackout is the same length cartridge as a 556 nato round and will feed. you cannot mistakenly shove a 7.62x51 NATO/.308 winchester round into a rifle lower/upper that is not an AR-10 derived design because there would be no way to even seat the magazine. even if you were to somehow mistakenly mount an ar10/762 NATO upper and barrel on an ar15 lower the only way you could try to get a round into the chamber would be to shove it in sideways through the ejection port

650REDHAIR 4y ago

300bo was done by AAC on its own though. There were some in the SOF community that were looking for better subsonic/more knockdown. I think 300bo is closer to 9x39mm in application.

topspin 4y ago

Blackout is limited to spec-ops use. More interesting is this: In April 2022 the DOD awarded substantial contracts[1] to Sig Sauer for the manufacture of the XM5 rifle and XM250 automatic rifle and the "6.8 Common Cartridge" as part of the Next Generation Squad Weapon Program. The new 6.8 is a much heavier and higher pressure round than the 556 and delivers far greater range and body armor defeat capability. The pressure is so great (80,000 psi, 551.6 MPa) that the case head (the 'back' part where firing pin hits) is made of stainless steel instead of brass; a 'composite' (steal + brass) case. I don't think that has ever been done in a military infantry weapon; all steel cases have been around a long time, but those are about cost saving as opposed to performance. 80,000 psi is pretty extreme in a rifle round. The high end of traditional brass case ammunition is 65,000 psi. That includes high performance rifle calibers like 338 Lapua Magnum and 22-250. Also, the XM157 Fire Control optic being built for these new rifles is remarkable: "variable magnification optic (1X8), backup etched reticle, laser rangefinder, ballistic calculator, atmospheric sensor suite, compass, Intra-Soldier Wireless, visible and infrared aiming lasers, and a digital display overlay." Due to the undoubtedly high cost these weapons will be limited to the 'first responder' combat forces and M4/M249 will be the mainstay for the rest for many years yet. But this commitment including the official designation of a new cartridge is a clear signal that the DOD is taking infantry weapon performance rather seriously. [1] https://www.army.mil/article/255827/army_awards_next_generation_squad_weapon_contract https://www.army.mil/article/255827/army_awards_next_generat... "The XM5 Rifle will replace the M4/M4A1 carbine within the close combat force, and the XM250 Automatic Rifle is the planned replacement for the M249 Squad Automatic Weapon"

walrus01 4y ago
> 80,000 psi is pretty extreme in a rifle round. The high end of traditional brass case ammunition is 65,000 psi. It is pretty extreme but I can't say I'm exactly surprised, metallurgy has clearly advanced quite a bit since the days when 556 NATO pressures in chamber were standardized 50+ years ago. If you have DoD budget levels of money to spend on a barrel you can clearly do higher. Barrels that meet 556 NATO spec are as cheap per unit as $100, a really nice one is $300. If it's not a problem that your barrel alone might cost $700 I can see this being totally possible.
4y ago

R0b0t1 4y ago

You've got it backwards, pretty much all cartridges were developed off of cartridges originally available to US hunters.