Sierra .223 Rem load data confusion

Discussion in 'Reloading Forum (All Calibers)' started by dboyles, Mar 8, 2012.

  1. dboyles

    dboyles

    Joined:
    Jun 7, 2011
    Messages:
    52
    Sierra publishes load data for .223 Rem, and separates it by bolt gun and AR-15 applications. In their .223 cartridge guide, AccurateShooter.com mentions the AR being more sensitive to pressure than a good bolt gun, and I've always assumed that to be the case.

    Why would the max published bolt gun load for a given powder/bullet/primer/COL be lower (sometimes significantly so) than the same for an AR-15? This is Sierra's load data for their bullets and Hodgdon powder (I've got a bunch).

    Code:
    components     bolt max   AR max   diff
    45gr / H322      25.3      25.7    -0.4
    45gr / H335      28.3      27.7    +0.6
    50gr / H322      24.9      25.2    -0.3
    50gr / H335      28.0      26.4    +1.6
    52gr / H322      24.3      25.2    -0.9
    52gr / H335      27.6      26.7    +0.9
    52gr / Varget    26.7      27.5    -0.7
    55gr / H322      23.9      24.3    -0.4
    55gr / H335      27.5      25.7    +1.8
    55gr / Varget    26.9      27.2    -0.3
    69gr / H335      25.7      23.8    +1.9
    69gr / Varget    26.4      26.1    +0.3
    
    H335 looks like what I'd expect: a reduced load compared to the bolt gun load. Varget looks backwards on the lighter bullets, and H322 looks backwards all around (except if you look at the data for the 63gr SMP with H322, where the bolt gun load is slightly higher).

    I'm not particularly concerned with the actual number on the published max loads (I'll work up the load from a safe starting point), but I'm curious about this pattern. Is there something about H322 (and maybe Varget) that would generally have you running a hotter load in an AR than in a bolt gun?
     
  2. Johnboy

    Johnboy

    Joined:
    Aug 13, 2008
    Messages:
    481
    by no means am I an AR guy.but I do want to take a stabb at it.

    really think about your question.shouldn't be too hard.a bolt gun works from the bolt up and all the pressure ends up OUT the barrel.an AR runs off the pressure to work the bolt each time.so the difference is that a bolt can only stand so much before bad things begin to happen.the AR uses the pressure to work so a little more pressure is needed to operate the bolt along with pushing the bullet out.

    one needs the energy to just work the bullet.the other needs it in two places at the same time.
     
  3. bigedp51

    bigedp51

    Joined:
    Oct 13, 2010
    Messages:
    1,936
    Two things to remember with the .223 and 5.56 NATO the leade or throat differences between military and civilian rifles. And military chamber pressure is measured at the neck of the cartridge and civilian SAAMI chamber pressure is measured at the mid point of the case body. The military method of pressure readings at the neck read higher than the same pressure measured at the mid point of the case body and this causes mass confusion.

    My Stevens 200 .223 has a 1 in 9 twist and a longer throat and I can safely shoot both types of ammo, a civilian .223 with a 1 in 14 or 1 in 12 twist will have a short throat and if military ammo is fired you will have pressure spikes above normal operating chamber pressure.

    Please read the link below with the explanation in detail.

    http://www.m4carbine.net/showthread.php?t=55149

    [​IMG]

    [​IMG]

    On top of this you have a multitude of different chamber reamers and throat variations.
    [​IMG]
     
  4. dboyles

    dboyles

    Joined:
    Jun 7, 2011
    Messages:
    52
    I might not be interpreting your responses correctly, or maybe I didn't phrase my question well. A call to Sierra may be in order.

    Why would H322 bolt gun max loads be lower than H322 AR-15 max loads when the exact opposite is true for H335?

    The data sorted another way:
    [​IMG]
     
  5. dboyles

    dboyles

    Joined:
    Jun 7, 2011
    Messages:
    52
    I emailed Sierra and here's what I heard back (quick response, too):

    That's about what I expected to hear, but I may ask Hodgdon if those types of results are typical.
     

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