what other caliber upper for 5.56 lower

Discussion in 'General Firearms Discussion' started by USMC_VET, Nov 4, 2014.


    USMC_VET Supporting Member

    if i was to do this what caliber upper would work with my 5.56 lower and what would be the best . what would be better 300 aac ,6.8 spc or 6.5 grendel
  2. I would go with the Black out. This is purely from watching the market. and noticing that 300 black out seems to have caught on and taken a hold. while the other two are few and far between.


    USMC_VET Supporting Member

    yep i've read the 300 aac is pretty much a .308 rd in disguise and that the 300aac will be a much better round for a AR platform
  4. If 300 can truly put the power down range that a .308 does. I will surely get one some day.

    I love .308 but god is it expensive
  5. Rachgier

    Rachgier Administrator Staff Member

    Sort of. I would loosely say that the .300 compares to the .308 in the way the .308 compares to the .30-06. Same caliber projectile, different casings resulting in different powder charges and subsequently diminishing effective ranges and stopping power as you step down. The .300 is a great second upper for your AR-15 lower to fire a .30 projectile without having to step up to an AR-10 platform. You can still go AT&T at a very respectable distance with the .300.
  6. Branth

    Branth Member

    It's not in the same power range. It's a 7.62X39 in disguise, sure, but it's no .308.

    The 30-06 throws a 150gr bullet at something like 2900 fps (2,820 ft-lbs)
    The .308 throws that same bullet at something like 2800fps (2,650 ft-lbs)

    The 300 BLK throws a lighter 125gr bullet at about 2,200 fps (1360 ft-lbs)

    Now, I like the cartridge. It's got more punch than the .223, and at reasonably close ranges it definitely has an advantage. It can also be easily suppresses for a super-quiet round that still packs a lot of punch. It also is a .30 caliber, which allows you to hunt in some states that outlaw .22 caliber for hunting.

    What it is not, though, is a long-range cartridge, or something that is competitive with the .308 or 30-06 in power.
  7. Bull

    Bull Just a Man Supporting Member

    Plus the added bonus of using the same mags.
  8. wganz

    wganz Supporting Member

    Other alternatives

    The .300 BLK is 7.62x39 Lite. At the LGS, the consistent stories are that the .300 BLK just doesn't cut the mustard with a >300# boar. The .300 BLK works best with pistol length barrels and subsonic rounds which may require you to Form 1 your AR to allow it to legally have a pistol length barrel. If your AR is a carbine, then either the 6.8 or 6.5 may be a better choice. I'll confess to being a 6.5 Swede fanatic but, in an AR carbine, the 6.8 SPC may be a better choice to step up the power ladder.

    Another alternative to consider, though a bit more pricer to build, would be to get a 9mm upper. This would allow cheaper practice and access to some indoor ranges that allow PCC's that would otherwise prohibit using a 5.56.
  9. LOL the 300aac is no 308 I have shot them both, ill take my 308ar over the 300
    Last edited: Nov 4, 2014
  10. Branth

    Branth Member

    And the same bolt! It's a cool one-part upgrade!

    You and me both! The .308 does have significant recoil though...
  11. also has the benefit of using the same cases as your 5.56. so after you shoot a few thousand 5.56 and save the brass. it wont be to difficult to reload them into 300 black out. and boom, you have a .30 cal hitting AR
  12. The nice thing about the .300 Blackout round is it uses the same 5.56 x 45 receiver and AR-15 magazines, but the round is more powerful. There are plenty of AR-15/M-16 magazines in the United States. You can also modify 5.56 x 45 brass to make the brass for .300 Blackout.

    I have read a 110 grain .300 Blackout round is pretty powerful out to about 300 yards. Any shot beyond 275 yards is long range shooting in my opinion.

    I would also get an 18 inch barrel if you do decide on the .300 Blackout round.
  13. bscar

    bscar Supporting Member

    From what I've read, I believe the .300blk is a .308 bullet in a 5.56 casing with the necked part removed.
    I've watched a video where the person was cutting that part off the brass casing, though they didn't do a full video of them reloading it all the way
  14. ajole

    ajole Supporting Member

    NE Utah
    Oh, come on you have a popgun AR, you have the .308.

    It's time to step up.

    .50 BMG upper.:cool:

  15. bscar

    bscar Supporting Member

    Unless the lower is made from solid cast iron, the first shot would probably disintegrate the lower.
  16. ajole

    ajole Supporting Member

    NE Utah
    Nah, just your shoulder.

    Honestly, they've been putting these out for over a decade in various models by various makers, and the AR's haven't fallen apart yet.;)
  17. The best thing about the .300 blk is that it can be sub sonic, still be accurate and have a good range. Just the thing for when one doesn't want to bother everyone in a neighborhood.
  18. greg_r

    greg_r Lifetime Supporter

    My second upper is the 300 blk for all the reasons stated above. I'm a bit surprised about it not being good for hogs as I've had no problems with it, nor have anybody else I know who uses it.

    If I wanted long range I would go with the 6.5 Grindel. Better B.C. than the 6.8.
  19. 5.7x28 upper!


    Those are cool... Pointless, but cool.

    Just step up your game to one of those .300WinMag ARs, they're only like... $5G... Haha.

    Sent from my iPhone using Hi-Point Forum
  20. wganz

    wganz Supporting Member

    One thing people don't consider isn't the damage to the lower which is minimal if at all; but, the increased # of shooters with detached retina's from the redirected blast coming from the muzzle brake. That is what changed my mind about getting one.

    A Savage bull barrel .300 Win Mag with good glass will do what 99.9% of most shooters will ever need and be less $$$. I got that advice from a long range tactical shooter that is in the top 3 here in Texas when I asked him about getting one.