Does heat affect ammo POI?

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  • Does heat affect ammo POI?

    Being fairly new to the rimfire scene I am at a bit of a loss. Recently purchased Sako Quad Varmint and Kahles 3-10x50 as a practice gun. It shoots one holers with a variety of ammo but last session I noticed groups open up to about an inch @ 60m all of a sudden. Having a think about things I realised the ammo I was using had been sitting on the tray of my ute in the sun and was a fair bit hotter than usual. Got some cooler stuff out of the cab and things settled down again. Ammo being used was Fed HV 40gn. Does heat cause this? as I am used to relying on ADI powders which I have found great when it comes to temp sensitivity.
    Thanks Jerry

  • #2
    Yeah mate, temp of the ammo can give you a massive variance to POI
    Found this link, maybe helpful

    http://rimfireshooting.com/index.php?showtopic=6758

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    • Jerry
      Jerry commented
      Editing a comment
      Interesting article, thanks for posting the link. The author basically found the opposite of what I did.
      Originally posted by FanTikkaTastic" post=5817
      Yeah mate, temp of the ammo can give you a massive variance to POI
      Found this link, maybe helpful

      http://rimfireshooting.com/index.php?showtopic=6758

  • #3
    In short, yes, heat will affect your ammunition.
    I recall reading a study years ago where the Rhodesians conducted a study on how hear affected the round in the chamber when that round was in the chamber for long periods of patrolling.

    They found that POI could be affected as much as 4 inches at 100m/yds (can't remember which).
    This was recently repeated by the Yanks in Iraq and Afghanistan and correlated.

    As you note, ADI is one of the best in the world for temperature stable propellants. I recall speaking to some US Army shooting team blokes who were a bit concerned about the increase in pressure they were experiencing with their ammunition whenever they shot down under.
    ---------------------------------------------------------------------------------------
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    Where we are, where we belong, where we should be.

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    • #4
      Not rimfire but still interesting and there must be some comparable effect on RF - In the Guns and Game Issue 79, July-September 2013 there is a very interesting article on the new ADI Outback ammunition by Briel Jackson. The author actually takes an oven to the range and heats up his ammunition and compares the POI of the heated to the non-heated rounds for the ADI and some comparable non-heat stable ammunition - the Australia stuff really did have less temperature variation. A very interesting read and well written article.

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      • Jerry
        Jerry commented
        Editing a comment
        Thanks for the replies fellas, may do some experimenting myself.
        Jerry

      • Savage
        Savage commented
        Editing a comment
        Originally posted by NewsteadVic" post=5829
        Not rimfire but still interesting and there must be some comparable effect on RF - In the Guns and Game Issue 79, July-September 2013 there is a very interesting article on the new ADI Outback ammunition by Briel Jackson. The author actually takes an oven to the range and heats up his ammunition and compares the POI of the heated to the non-heated rounds for the ADI and some comparable non-heat stable ammunition - the Australia stuff really did have less temperature variation. A very interesting read and well written article.
        AR2206 was bad for heating up on the mound and changing POI when fullbore shooting, I believe AR2206H was ADI's answer.

        For accuracy purposes I have always tried to keep ammo out of direct sunlight/heat. Especially when loading to the max as heat can sometimes tip a hot load over the edge.

    • #5
      Another issue when rimfire ammo gets hot is the wax the bullet is coated in, have a close look as it can melt off or run to one side. May not sound like much but ammo consistency is paramount in rimfire accuracy.

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      • #6
        Yes. In general, muzzle velocity will increase with temperature. So I. Theory, you will be shooting high with warmer ammo.

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        • Jerry
          Jerry commented
          Editing a comment
          All good advice, thanks. Eventually I will get the hang of the rimfire, just frustrating after handloading for 25 years not to be able roll my own. In saying that I am enjoying shooting the little thing, trying heaps of different ammo and it is definitley helping with trigger control etc. Interesting to note that after only about 20 rounds even the set trigger can feel heavy.

      • #7
        A guy asked a similiar question on an other forum but no one really knew the answer, maybe someone could help ?
        If you are shooting in a competition and you have a round in the breech and are holding off for the wind . how long do you think it would take to affect the chambered bullet or in rimfire do you think it shouldnt be an issue ?

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        • several
          several commented
          Editing a comment
          I remember seeing a story on Canadian snipers in Afghanistan, and they set a few rounds aside to warm up in the sun in case they needed to go a little further to find a target. So I assume if those guys are doing it, they're doing it for a reason.

        • danandria
          danandria commented
          Editing a comment
          Hi the Jet,
          In my Anschutz often a chambered round will drop if unfired for about a minute, I asked some very experienced shooters about this at a comp last year and they said it was due to condensation build up in the barrel. Now any round it becomes a sighter after a minute waiting.

      • #8
        Not a rimfire (obviously...) but the Soviets provided complete tables for firing the Mosin Nagant M1908 7.62x54R round in different temperatures and at various ranges.
        Basically 15° C was the standard temperature with no adjustment necessary.
        Above that, the tables indicate lower aimpoints (4cm lower at 300m at 35° C for example) while lower termperatures require higher aimpoints.
        Member of the Aunty Jack Firearm Appreciation Society - "Now be a good little Aussie and learn how to shoot or I'll rip your bloody arms off......and I will too!"

        "Have you tried unloading it then reloading it?" - Roy Trenneman on fixing firearm problems

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        • #9
          Thanks for that Dan
          I always wondered about this . Condensation I would have never thought of thats for sure.
          I will put her into the ground from now on myself as you are right come to think of it they do drop a bit never put it together though.
          I just get a bit impatient for the wind to ease sometimes and when it does want to put as many scoring shots in as possible during the condition.
          I cant remember how many I have screwed up shooting that last bullet to watch it get blown off the bull by the breeze that hasn't made to you yet at the bench or by taking my eyes off the flags to aim.
          Thats one of the challenges of benchrest shooting really , the reading of the wind and especially shooting through it as sometimes you have to do to finish in time.
          kind regards Ben

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          • #10
            Also obviously not rimfire, but have heard of IPSC shooters putting their ammo in the sun just prior to a comp to give the power factor a bit of a nudge Lol

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