Sensible and appropriate AR ammo?

Discussion in 'Ammunition & Reloading' started by supergus, Oct 5, 2009.

  1. supergus

    supergus New Member

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    O.K. I have an AR with a 1:7 twist. After reading several articles as well as the ABC's of Reloading, I realize that with my twist rate, I can shoot pretty much any weight of bullet, from 50gr. up to 80 gr. First off, do you agree with this assumption? Secondly, if this the case, what is a good CQ bullet weight? And also, what would be a good longer range weight, say past 200 yds.? Lastly, what would be a good weight for 100-200 yds? Does it really even matter at 100 yds? TIA
     
  2. Highpower

    Highpower New Member

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    Personally, I stay away from the 50 grainers in a 1:7 and consider 62gr to be my minimum for stability. I generally shoot 69 gr out to 300 yds, and 77 - 80gr beyond 300. But that's just me.... ;)
     

  3. RL357Mag

    RL357Mag New Member

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    +1 to what Highpower said. I have an RRA with a 1:8 and it shoots 69gr. Sierra's and 68 gr. Hornady HPBT's very accurately. 55Gr. Remington FMJ's don't group any tighter than about 1.5 - 2". I've never shot anything heavier than 69gr., but I'm willing to bet that the 75-80 gr. bullets will shoot better than the 69gr. bullets. National Match competitors use 77 - 80 gr. bullets out to 800 yds., the only problem is that they have to be loaded singly, since they will not fit in the magazine.
     
    Last edited: Oct 6, 2009
  4. ranger_sxt

    ranger_sxt New Member

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    Your initial assumption is correct: your barrel will stabilize anything from a 50 grain to an 80 grain bullet. There does exist a 90 grain bullet, which your barrel will stabilize as well.

    For my shooting, I tend to 55gr FMJ for anything from the muzzle to 300 yards.

    1.) One should not expect anything greater than 2" groups from a 55-grain FMJ at 100 yards. The exposed lead at the base of the bullet has a lower melting point than the copper jacket. The lead will melt slightly during the firing process and throw the concentricity of the bullet out of whack.

    2.) Depending on the ranges, 69 grain bullets should shoot better. The 69 grain bullet has a better ballistic coefficient. The 75-80 grain bullets tend to be used at longer ranges because the shooter does not have to compensate as much for the wind.

    3.) The Sierra Matchkings in 77 grain and the 75 grain Hornady bullets can be seated to magazine length. In fact, soldiers and Marines in the Squad Designated Marksman role are using 77 grain Sierra MatchKings.
     
  5. Highpower

    Highpower New Member

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    Sierra recommends a 1:6.5" twist barrel.

    Absolutely correct. Which ticked me off awhile back because I drove all the way out to the Sierra factory (3 hrs from home) to purchase some "seconds" and they were completely out of them. (ALL bullet types!) I talked with one of the ballisticians and was told that the plant was producing one bullet - and one bullet ONLY at that time. The 77gr MatchKing (cannelured) -- for the US military.

    I'll be glad when they get back to a "normal" production schedule. :)
     
  6. supergus

    supergus New Member

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    Thanks for the feedback guys. I'm heading to the range on Thurs. and I'm bringing some Hornady 75 gr. Match ammo and some Federal Fusion 62 gr. for comparison at 100 yds. However if I can get comparable accuracy @ 100 yds with 55 gr. I'll use those for practice ammo.
     
  7. RL357Mag

    RL357Mag New Member

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    Quoted from Sierra's 4th Edition 50th Anniversary Manual:

    As for loadings and recommended powder charges given for this bullet, the following also appears under the 80gr. MatchKing HPBT in the same manual:

    You would be hard pressed to find SAAMI approved reloading data that endorses seating a long, heavy bullet to an OAL of 2.26". Additionally, depending on the type of chamber you have, you may not even be able to chamber a round using an 80 gr. bullet which has been properly seated to an OAL of 2.550". Many modern chamberings are of the .223 Remington variety, and do NOT posess the longer leade of the military 5.56 or Wylde chamber.
     
  8. ranger_sxt

    ranger_sxt New Member

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    Please re-read the highlighted section.
     
  9. RL357Mag

    RL357Mag New Member

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    Please re-read the underlined text...:rolleyes:

    First of all numbnuts, I'm giving the OP information on the 80gr. bullet which he mentions in his question, secondly, while a 77gr. bullet CAN be seated to the max OAL of 2.26", most National Match competitors, as well as knowledgeable reloaders who strive for accuracy, seat their longer heavier bullets out to meet the lands and grooves because this yields better accuracy. Anything heavier than 77 gr. will NOT fit in a magazine and should NOT be seated to the same depth as the 77gr. bullet. I responded when I saw the 80 gr. bullet mentioned because many reloaders go out and buy 80 gr. bullets without realizing that they will NOT fit in their magazines, and seating them deeper so that they do fit, can be dangerous!
     
    Last edited: Oct 8, 2009
  10. robocop10mm

    robocop10mm Lifetime Supporting Member Lifetime Supporter

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    At ease, gentlemen. No need for name calling. Lets calm down a bit and remain civil.

    Back on task... My 1/7 barrels shoot just fine (1" or so) with 55 gr FMJ handloads. WWB M-193 does not do as well. You should avoid the light weight "match" or "varmint" bullets as they tend to have thinner jackets. The combination of high velocity, thin jacket and fast twist can easily lead to bullets vaporizing shortly after leaving the barrel. The gray puff about 15' down range is a pretty good indication you have surpassed the rotational max for a given bullet.
     
  11. Highpower

    Highpower New Member

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    I believe that the way this was written, it was misconstrued to mean that BOTH the 77gr and 80gr bullets had to be singly loaded. The 80 gr bullet was not singled out here, therefore your meaning was not perfectly clear. No harm no foul....

    Although as you say, the 75 / 77gr bullets do not HAVE to be seated to magazine length, every NM shooter I've met personally that shoot these bullets DO load them to magazine length for one simple reason. Rapid fire strings in the National Match courses. It's the KISS method. If I loaded some longer for the slow fire stages, I can almost guarantee you I would get them mixed up at some point, and that would just ruin my day - so I won't chance it myself. ;)

    The 80 grain x-ring seeking, mini-missiles are another story entirely because you are dealing with slow fire strings at the 500+ yard distances, and have plenty of time to do so. My 80gr loads are stretched to 2.555" OAL for my Colt H-bar w/ 1:7 twist, and they are still .020" off the lands in the NATO chamber. My EA rifle with a Krieger 1:7.7 only needs a mere 2.390" OAL for the same jump to the lands.

    There again, I have to be VERY careful to bring the correct length ammo with me depending on which rifle I have with me. :rolleyes:

    robo: Excellent explanation on exceeding the RPM's of the lighter weight thin skinned projectiles.