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AR15 equivalent for .308

Discussion in 'Rifle Country' started by Grayrock, Dec 11, 2019.

  1. Grayrock

    Grayrock Member

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    Are there any AR15 uppers chambered for a cartridge that meets or exceeds the performance of the AR10 rifles in .308? I know there is a whole host of choices out there ranging from 6.5 Grendel to .50 Beowulf. Anything match the ol' 7.62 X 51?
     
  2. mjsdwash

    mjsdwash Member

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    358 yeti claims similar energy levels, but I won't believe it until I see it in person. The SPC, and Grendel are the most powerful I know work.
     
  3. Varminterror

    Varminterror Member

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    A point of clarification - you’re asking if any <2.3” cartridge, containing 25-30grn of powder can perform equally to a <2.85” cartridge burning 40-50grn of powder........

    Trajectory is one thing; it’s pretty easy to meet or beat a 308win for ballistic trajectory, and that whole “velocity squared thing” might offer a few cheats towards matching energy, but c’mon man, we’re talking about mini-cartridges versus short action cartridges. A few rounds like 7 Valk and 358 Yeti have claimed amazing numbers, which I’ve yet to see proven outside of the designers’ webpages - numbers which sincerely don’t add up. Some magical means to push a heavier projectile to a higher velocity with a lower operating pressure and less powder... See the problems here?
     
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  4. troy fairweather

    troy fairweather Member

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    I'd think the wssm rounds would be the best bet.
     
  5. LoonWulf
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    LoonWulf Contributing Member

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    If you use a large frame extension, and bolt, then go with a fatty like the WSSMs, or even something like the SOCOM, you could likely out do the .308.
    I know the .300Oly would out run the .308, at least with lighter bullets.
    If your considering a "standard" ar-15 cartridge youll be hard pressed to get .308 performance.
     
  6. spazzy

    spazzy Member

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    The big bore choices (450 bushmaster, 458 socom ect) match the energy of the 308 at close range but the big fat bullets run out of steam much much faster.

    That being said I am shopping for a bushmaster for deer hunting next season.
     
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  7. marksman13

    marksman13 Member

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    The simple answer is no. Everything is a compromise. You want a lighter, slimmer, better handling rifle? You’re gonna have to give up some powder space. Once you start giving up powder you’ve either got to push the bullet slower or run a lighter bullet. No free lunches. That said, 6.8 SPC, 6.5 Grendel, 450 Bushmaster, 50 Beowulf, and 458 SOCOM, as well as a host of less popular cartridges exist for the AR-15 and all of those make dandy whitetail cartridges inside of most people’s effective range.
     
  8. gotboostvr

    gotboostvr Member

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    Like others have said, you're gonna have to make a trade off.

    You can be as flat shooting, but less powerful with 6.5 Grendel.

    You can be as powerful, but not as flat shooting with the various 45-50cals.

    You might be able to get away with one of the Winchester Super Short Mags. But that's its own set of issues. Expensive, custom made uppers and brass that's unobtanium.
     
  9. someguy2800

    someguy2800 Member

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    The 358 yeti is legit. I have had one for about 3 months. It can meet the claimed 2600 FPS with a 180 grain bullet from a 16” barrel, I have done it. There is only one powder that will do that though and my particular rifle did not shoot accurately with it, but there are several powders that will get it to 2500 FPS with a speer 180 hot core. My hunting load is with CFE BLK loaded in cases made from trimmed and formed 270 cases right at 2500.

    I would say properly loaded it will be just as capable as a 308win from the same 16 or 18” barrel out to about 200 yards. Past that range the ballistic coefficient of a good bullet in the 308 will start to walk away.
     
  10. Orcon

    Orcon Member

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    There used to be a cartridge called the 30 Remington AR, it's faded into obscurity though.
     
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  11. someguy2800

    someguy2800 Member

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    It’s is still not totally released yet but there is a modern replacement. Not quite 308 performance but not far behind in short barrels.

    https://www.maddogweapons.com/30-sabercat.html
     
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  12. hq

    hq Member

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    How about a lightweight .308 AR, loading the ammo as hot as you like and not compromising anything by trying to stuff equivalent performance in a much smaller frame AR15?

    Just a thought...
     
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  13. Charlie98

    Charlie98 Member

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    I think that falls under 'if it was so easy, everyone would be doing it.'
     
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  14. Varminterror

    Varminterror Member

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    The WSSM’s might be as close as you can get, with an AR-15 sized non-AR-15, but you’re still nipping at the .308’s heels at best, and carrying a handful of headaches with them. The case capacity is really close, ~95%, but we’re giving up a bit to fit into <2.3” mags.

    I have had Mike Milli’s uppers in 243wssm and 25wssm. The 25 throws a 120grn bullet at the same speed a 308 win throws a 150, and you have to short seat 120’s to fit into the magazine - which leaves you begging for enough room to fit 45grn powder under the bullet. Some factory 25WSSM loads with lighter bullets would fit in the mag, some wouldn’t. The 243wssm is actually more challenging - the long 100-115grn bullets have to go REALLY deep to fit into the mag, and only gets up to about the same speed as a 308 with 125-130grn bullets. I don’t recall any factory ammo except light 50-55’s fitting into the mag. It might not seem like much, but a bumping from a 100 grain pill to a 125 at the same speed is a 25% increase in momentum and kinetic energy.

    The advantage of these WSSM’s, of course, is increased BC and SD - despite giving up a little muzzle velocity and/or a little bullet weight. I’d readily consider a .24SD 100grn 24cal bullet as a deer bullet, while I don’t care for a .19SD 125grn 30cal bullet for deer - despite 25% greater energy and momentum on the 30cal. This is the same challenge we see with the .358 Yeti - pushing the same bullet weight to the same speed, but lower BC and SD. A 180 30cal has an SD of 0.27, while a 180 35 cal falls to .20 - meaning one’s a deer rifle, one’s an elk rifle.

    If your yardstick is hunting field utility, then a handful of things thrown from an AR can harvest almost any game which can the .308win, within typical circumstances, with a slight nod for the .308win in atypical circumstances.

    If the yardstick is ballistic performance, then it’s game of horse grenades, where “almost” has to count.

    All of that said - far, far more of us carry AR-15’s than do 10’s. For good reason.
     
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  15. Orcon

    Orcon Member

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    Stop it, I'm trying to save my gun allowance for something else and I've already had too many distractions.
     
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  16. someguy2800

    someguy2800 Member

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    I didn't even think to mention it but you can have your cake and eat it too. There are 2 companies building proprietary AR's chambered in 308 that are near as makes no difference the same size and weight as an AR15

    https://dpms-gii.com/full.html

    https://pof-usa.com/firearms/revolution-di/

    I have handled the DPMS and I must say if someone handed me one in the dark I don't think I could tell that I wasn't holding an AR15. They are quite reasonably priced too. Only downside really is that they are limited in aftermarket support since they are largely proprietary. I am hoping and praying that the aftermarket picks this up and starts to standardize it. I want one in 338 federal.
     
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  17. Arkansas Paul

    Arkansas Paul Member

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    I don't know about "exceeding performance", but take a look at the .277 Wolverine.
    It looks good.
     
  18. jmr40

    jmr40 Member

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    If you're trying to duplicate velocity numbers with similar bullet weights you're chasing unicorns in an AR platform. If you're trying to duplicate performance on game the 6.5 or 6.8 offerings are as close as you're going to come.
     
  19. mcb

    mcb Member

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    Scrounge up a 30 AR Remington upper. A proprietary AR-15 upper that fits on a standard AR-15 lower. Shoots a 30 caliber bullet ~150gr or lighter at about 150-200 fps slower than a 308 Win from a similar barrel length. They are hard to find, Remington quit making them and there is little support for the cartridge but if you reload you can make it work.
     
  20. mshootnit

    mshootnit Member

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    What most people who do not do physics calculations very much, yourself included, do not realize is that when we are talking about commonly debated projectiles and commonly debated velocities, difference in mass is typically much larger than the corresponding observed difference in the speed (technically you should not use the term velocity unless you also include a direction).
    This explains why the energy of heavier projectiles usually always trumps lighter faster ones when we are talking sporting rifles even though the velocity is squared. There is no Kinetic energy vs. mass debate. There are only people with a glancing view of a physics book who have not fully investigated the situation.
     
    Last edited: Dec 12, 2019
  21. rbernie
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    rbernie Contributing Member

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    Putting aside the ad hominem - can you restate this in a way that allows simple folk like me to understand your perspective?
     
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  22. mshootnit

    mshootnit Member

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    Simply put, in common calibers and with common velocities often the difference in mass of the two bullets being compared is so much larger than the difference in their velocities that even though the velocity is squared in the calculation, the heavier projectile retains more energy.

    Note that the difference in mass between a 50 gr. Bullet at 3000 fps and a 150 gr. bullet at 2800 fps is 300% while the difference in speed is less than 10%
     
  23. mshootnit

    mshootnit Member

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    Sectional density by itself means very little when comparing bullets for deer hunting. It is not the shape of the bullet going in that matters it is what the bullet does on contact that matters. A 125 gr. 308 bullet properly constructed will wreck a deer regardless of the SD.
     
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  24. _Robert

    _Robert Member

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    What would I do? (considering my state doesn't allow hunting with .223)

    6.5 Grendel if deer hunting was my first priority. 6.8 SPC & 7.62x39 should be considered too.

    6mmAR (based off of the Grendel) if varmints were my quarry.

    Why? Because these 2 cartridges are not "too far off of the reservation" as far as components are concerned, both have good long range performance and both can effectively harvest medium sized game.

    I'm considering a 6mmAR build during 2020.
     
  25. jmorris

    jmorris Member

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