308 cartridge and free air space.

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  • 308 cartridge and free air space.

    Hope it makes sense .
    I am new to reloading in actually doing much though I understand the principles and do some for 308.
    I realize some cases are different capacity to others.
    Also understand the priciple of seating close to the lands ans so forth.
    I have basic equipment and also have comparitor and good steel verniers and a reliable accurate set of scales.

    What I do need to know is how much free space effects the loads and is there a percentage to weight ratio.
    I load a variety of once used full lenght sized brass and load it close to the lands.
    The confusion is in some cases in 308 its nigh on impossible to get more than 44 grains of 2208 with out the powder coming up the neck of the case.
    PPU and Magtech are like that and seem solid enough brass other wise.
    Some other brass I can or could easy enough go all out and get 46 grns in but mates I know prefer around 45.5 or 45.7 and the only difference is that free air space in the different cases.
    No loads are compressed and 308 does not seem to give a dam about the jump.
    Wheres the medium point here ? at the shoulder neck junction or below some where in the angled section of the shoulder ?.
    I am trying to duplicate Hornady`s SST as they just shoot like crazy compared to others.
    The Nosler 150 Ballistic tips might just be a tad softer but the explode on any sized animal from 50 meters to several hundred the just blow up ex Bang flops.
    Mainly shoot goats from rabbit sized to full size the results the same with Noslers -- big holes and dead goats.
    In an Omark s) I know I can go 46 grns but I don`t want to if I can do as well by using seating depth and a bit less powder to get the same results.
    I like the idea of having a fair amount of case neck holding the case for improved accuracy --works in the 222 as well one of its great points --long neck case.

    Experience and Ideas please any one.

    [center]
    Don’t poke the snake, walk around it and come back later with a double-barrelled shotgun and blow its [email protected]#!ing head off!.

    Australia in future, the outcome is the same, a bloody dictatorship run on the whims of a very few ego-centric pathological elitists.

  • #2
    For hunting distances, a moderate load that works in your rifle is all that you need. If chasing targets at 800 + , the highest safe accuracy node for you rifle/ brass combination will give best results.

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    • #3
      Best practice is zero air gap. How to achieve this will depend on powder choice, case capacity, seating depth, as well as the length of the projectile, ie how much is in the case. A rule of thumb, not an absolute is to not seat deeper in the case than shoulder level. This ensures all force is on the rear of the projectile.

      You will find the SST are long for their weight, compared to others.

      Sticking to one case brand will be a good thing as well.

      Good luck!

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      • Guest's Avatar
        Guest commented
        Editing a comment
        Originally posted by Oddball" post=39346
        Best practice is zero air gap. How to achieve this will depend on powder choice, case capacity, seating depth, as well as the length of the projectile, ie how much is in the case. A rule of thumb, not an absolute is to not seat deeper in the case than shoulder level. This ensures all force is on the rear of the projectile.

        You will find the SST are long for their weight, compared to others.

        Sticking to one case brand will be a good thing as well.

        Good luck!
        Not having a go, curiosity is my main drive here, how is zero air gap best practice? What advantage does it bring?

    • #4
      one thing I've noticed is if you have a longer tube from your powder thrower feeding your shells, it helps settle the powder in the case, allowing more powder in the shell.
      same as a powder drop tube.
      that is if you wanted more powder in them.
      I've never heard of an 'actual' ratio, but some of my best performing loads have sometimes only been a case that's 80% full.
      when you think about it,......that's quite a lot of air.
      as oddball said,...pick one type of brass and try that one for a while, only changing powder and pills.

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      • #5
        smoother burn rates, less erratic burn characteristics.
        its supposed to be more consistent from shot to shot.
        or something like that.
        but there's several other factors that come in to it. e.g; types of powders.

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        • Guest's Avatar
          Guest commented
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          Curious... Not sure how the physics of that theory work. I better have a long think about that one. Currently I find that velocity stability and consistency can be achieved with a significant air gap, hrmm it comes down to consistent pressure curves and the amount of air should not directly impact consistency of the pressure curve I would have assumed, better look into it.

      • #6
        If you load from a box, singularly into a chamber, air gap is irrelevant. If you shoot with cartridges in a magazine, it can become an issue.

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        • NoFerals
          NoFerals commented
          Editing a comment
          Thanks all ....so it seems as I do load single and for hunting there laying any which way in the tray or pocket or whatever.
          I had this idea from some place once and I still do it when shooting off a bench or target shooting I give the cartridge a couple of gentle taps on the base before chambering them.
          Get some odd looks but it does seem to help a bit as I am under the impression it settled the load against the primer and leaves the air space behind the projectile.
          Dunno where I learned it from but it seems to work.
          No doubt having all your loads base down in the green boxes and having a ride to the range would settle them in the same way.
          Damit I need to rearrange my hunting boxes as they sit base up in the tool box / container they live in.
          All my racks / shell holders are just old styrene s in a fixed tray in the ute console.
          Makes the shells easy to identify the primers to select for ranges as it varies a lot / color for different weights 130 hp are red / ssts are /some thing else/ green tips are green/ etc.
          Thanks shooters.
          NF.
          Originally posted by Oddball" post=39375
          If you load from a box, singularly into a chamber, air gap is irrelevant. If you shoot with cartridges in a magazine, it can become an issue.

      • #7
        a bit like premature detonation in a car combustion chamber.
        erratic burning = rougher running.

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          Solid state fuel operates a fair bit differently, it also doesn't require the same local conditions. The quantity of powder should dominate the process over theminiscule amount of relatively inert gas being present. I appreciatte that burning could vary by position of the powder in the case but we are more concerned with the pressure wave developed when it comes to internal ballistics, burn rate dominates not burn direction...
          addendum here is initial ignition, but that's a different kettle of fish again...

      • #8
        A compressed or near full charge will ignite from the rear and have a consistent burn rate from shot to shot. An 80 % charge may have the air at the back, top or front, depending on firing angle, which will affect ignition and pressure curve. Probably not much in it, but small changes in seating depth and powder charge can also tighten groups.

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        • #9
          Your gunna love this and you might even think its BS but true i pulled two double headers today.
          First one I missed an easy shot and was abittpeeved but its close like 120 yds and I made the driver wait till th uggers line up and I will get two with one shot.
          Yeps did that redeemed myself and the wasted ammo on the miss.
          End of the day and a couple of scruffy goats ran out from under a bush at around 100 yds in a different spot -- no time to lineup right handed and awkward left hand but here goes pinged em both through the scone with one shot as they lined up and were heading into a few bushes and gone.
          You just gotta love 308 and Omarks ...and being ambidextrous I do .
          Missus don`t care I just had to share that one its like a double possible
          [center]
          Don’t poke the snake, walk around it and come back later with a double-barrelled shotgun and blow its [email protected]#!ing head off!.

          Australia in future, the outcome is the same, a bloody dictatorship run on the whims of a very few ego-centric pathological elitists.

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          • Guest's Avatar
            Guest commented
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            Nothing more really to add to this that hasn't been said.

            I do prefer dense loads but there's no real science in it, just a preference so I know I always have consistant ignition.

            I think it would have to be heaps of free space to make any real difference.

            My 168gr Amax load is 46.4gr of 2208 & they are pretty much stuffed full, I have to tap the cases to settle the powder before seating but Damn..they shoot!

            Mick.
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