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5.56mm EBRs that can handle more powerful 5.56mm like MK262

Discussion in 'Rifle Country' started by .cheese., Jun 16, 2007.

  1. .cheese.

    .cheese. Well-Known Member

    Let's discuss more powerful 5.56mm rounds like MK262 and which rifles (and twist rates) work with them? I assume a faster twist rate is needed, but I'm not sure how fast exactly.

    Also, anybody know anything about barrel requirements?

    And what other more powerful 5.56x45 cartridges are there? Hornady TAP?

    What do you guys know about these newer developments (not that new, but new comparatively)
  2. Langenator

    Langenator Well-Known Member

    You really need to define "more powerful."

    The Mk 262 Mod 0 and Mk 262 Mod 1 (the Mod 1 features a cannelure which the Mod 0 lacks) can be fired with no problem from the standard M16A2, A4, and M4.

    The round is not loaded to chamber pressures which exceed the defined specs for the 5.56 NATO round. It simply features a heavier bullet than the standard M855 greentip round.

    Barrels on US military 5.56 weapons feature a 1/7" twist. However, the 77 grain bullet can be adequately stabilized by a 1/8" barrel.
  3. Sonic

    Sonic Well-Known Member

  4. .cheese.

    .cheese. Well-Known Member

    what I mean by more powerful is additional ability to reach out and touch somebody.... or perhaps punch somebody... you choose your analogy. ;)

    Does the MK262 Mod 1 work fine on LMT rifles? I assume it would as the military supposedly uses some of LMTs gear.
  5. Don't Tread On Me

    Don't Tread On Me Well-Known Member

    1/7 twist is more ideal for the heavier stuff. It will put more RPM's on it which comes in handy in freezing cold weather.

    MK262 is hot stuff. It isn't dangerous, but it is definately hot. Hot enough to where brass takes a beating and life is shortened. MK262 is something like 2848fps from a 20" barrel for a 77gr bullet. Most saami data is in the 2600fps range. Remember that a round gets even more pressure after cooking in a blazing hot chamber after a few rapid fire magazines.

    Any NATO chambered AR-15 should be able to handle it fine. I don't think anyone chambers any barrel for an AR-15 that would be dangerous. The manufacturers and barrel makers automatically protect against much of the danger by making chambers that can safely shoot the heavier bullets at NATO pressures. They look at what's on the market and what people can handload and go from there. There are some extreme exceptions though.

    The Mk262 is pretty much the ultimate in 5.56 ammo these days. I also believe it is the pinnacle of the 5.56x45. People have experimented with 80gr, 90gr and even 100gr. They are simply pushing the limits past practicality and are even counter productive in many ways. 5.56 has come a long way. There isn't much left to do in bullet design either. The 69gr and heavier stuff is long - so it has earlier yaw effects. The heavier 5.56 fragments much more as well as more often. People tend to forget that the 55gr and 62gr stuff looks fantastic when they do fragment, but they don't always. The match-grade thin jacket stuff is much more consistent, as well as having more fragmentation effect.

    I don't see anything coming out in the future that is magazine-fed that can outperform the Mk262 and being worthwhile. If Mk262 isn't getting the job done, it's time to switch cartridge entirely. This cows been milked.
  6. Jeff White

    Jeff White Moderator Staff Member

    All you need is a good barrel with a 1/7 twist. Some people have reported acceptable results from 1/9 twist barrels. But I think that is going to vary by individual barrel.

    Contrary to popular internet lore, since the advent of the 75 grain and up bullets, 1/7 is the most versatile twist rate for an AR. It will handle everything from 50 grain Federal to 55 grain M193 to the long M856 tracer to Hornady 75 grain and MK262 77 grain.

  7. redloki

    redloki Well-Known Member

    I found some Sierra 77gr SMK's with a cannalure that are used in the Mk 262 Mod 1 at a gunshow a while back. I took some pictures since you don't find these everyday.

    Attached Files:

  8. DMK

    DMK Well-Known Member

    I have a 1/9 inch Bushmaster that will shoot good groups with 75gr at 100 yards, but 77gr will open way up (still no keyholes though). That leads me to believe it's right on the edge of stabilizing the 75gr even.

    My 1/7 twist rifles love 77gr on the other hand. But they don't shoot 55gr. as well as my 1/9s

    Cool pic Redloki. :)
  9. .cheese.

    .cheese. Well-Known Member

    Thanks guys.

    While we're at it, anybody here have any data regarding heavier/longer 5.56 out of 16.1" barrels? Such as FPS, etc.?
  10. Bartholomew Roberts

    Bartholomew Roberts Moderator Emeritus

    I'm getting around 2582fps out of my 16in. barrel with 75gr Black Hills blue box. You can get a bit hotter with Mk262 but accuracy suffers some (though still way better than ball).
  11. Onmilo

    Onmilo Well-Known Member

    It should be noted that MK262 is a brass jacketed lead core bullet.

    It is designed as an anti-personnel cartridge not an armor plate defeating cartridge so this designs 'power' comes from the fact it retains sufficient energy to effectively neutralize a lighly armored combatant at ranges exceeding the current 62 grain cartridge.

    Power is a relative thing and soldiers operating in the Iraq and Afghanistan fields consider the 5.56 sufficiently adequate to 400 meters unless the opposing combatants are behind heavy cover.
    In those cases the switch is made to 7.62 and .50 machine gun and 40mm grenades.

    One uses the correct tools for the task at hand and the M16/5.56 will never be the one and only cartridge anymore than the M1 Garand/.30/06 was in WW-2 though the .30/06 was a much better overall choice for open field combat, soldiers still preferred .30 Carbines, shotguns, and .45 submachineguns and the old standby hand grenades for house to house and urban action.
    The more things change the more they remain the same.
  12. ftierson

    ftierson Member.

    The M262 Mod 0 was developed in an attempt to bring back some lethality for the 5.56x45mm NATO in M4 length barrels...

    M193 and M855 work reasonably well from 20 inch barrels, where the velocity is still up in a useable range...

    Shooting the same ammo out of a 14 inch barrel just doesn't make people shot with it lie down well...

    Increasing the bullet weight (even at the expense of even more velocity loss) has helped the M4...


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