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Thread: Snow in the barrel?

  1. #1

    Snow in the barrel?

    After reading a funny story by mauser66 in the reloading forum I thought to post something which has given me cause for some consideration of late.

    Why is snow in the barrel a problem? Note that I'm not denying it is a problem, I'm just asking for someone to explain the mechanism by which snow causes your barrel to blow up.

    The way I see it as the bullet travels down the barrel it is preceeded by extremely hot gas at approx 6,000 fps and I would have imagined that this gas would easily displace snow or the occasional drop of water or oil. However, there is no question that people have barrels blow up due to water or whatever being in there. So, does anyone know how it works?

    I appreciate that if you have enough snow then the gas may not move it before some pressure builds up but I would have thought that pushing a little snow out of the barrel requires much less pressure than forcing the bullet into the rifling. Also I've seen some reports which indicate that shooting a bullet which is too big for your barrel is unlikely to cause serious problems as the pressure swages it down to fit. I would imagine, once more, that swaging a big bullet into a small hole to be much more dangerous than having a little plug of snow in the barrel, I just can't see how swaging the bullet could cause less of a pressure spike than blowing out some snow.

    So, has anyone any ideas? Please note that all experiences seem to indicate that shooting a rifle with snow in the barrel is potentially fatal and a "very bad thing" so you shouldn't do it and I'm not suggesting it is safe, I'm just interested in the processes that make it "not safe."

  2. #2
    Caorach, I would reckon on it being a chicken & egg thing, as in which comes first, the obstruction moving, or the column of expanding gas behind the bullet exceeding the pressure required to do damage.
    Last edited by finnbear270; 22-02-2010 at 15:30. Reason: brain fart!

  3. #3
    Couple of thoughts:

    1) you have a barrel well jammed in and full of snow - ie a good six / seven inches of solid snow

    2) snow is actualy a pretty good insulator and also requires a huge amount of energy to turn it inot water - try making a cup of tee using water which is just above freezing / snow / ice - it takes about five times as long.

    3) all the hot cases are behind the bullet and the bullet forms an eficent seal to the barrel

    Thus you jam your barrel in the snow and then squeeze the trigger.

    If any hot gases could get past the bullet they would only melt the snow they are in contact with. OK as air in front of bullet is compressed against the snow in will heat up. So we now have a situation where we an incomressable liquid ahead of a bulet with mounting pressure behind it and the liquid is blocked by solid snow - the only place for the pressure to go is sideways out of the sides of the barrel causing a burst.

    The best thing to do with snow is to not get your barrel blocked, keep checking that it is clear and if you are at all worried, to out a piece of insulation tape over the muzzle to keep snow out. Bullet will shoot straight trhough insulation tape.

    I also carry a flexible pocket sized cleaning rod on the hill in case you ever get a block - it does happen.

  4. #4
    I wonder if you might not have something HeymSR20, maybe it is the water left behind by the snow that causes the barrel to burst?

    I believe that hot gas goes up the barrel in front of the bullet, slow motion film shows this quite clearly, so I guess the gas gets past before the bullet seals the barrel.

    If this gas were to melt some of the snow then when the bullet hit the water at high speed you would have a problem. I suspect that a few drops of water in the barrel are not a problem with an unplugged barrel as the hot gas can blow them out of the way. But when they are trapped behind snow then the situation is different. Does that seem reasonable?

    I almost always carry the rifle with tape over the muzzle, even with the moderator on and often even on dry days. When I push through trees and undergrowth I suspect there is the chance of some pine needles or similar getting down the barrel and that can't be good. So, when I remember the tape goes on.

  5. #5
    I would put it down to basic Hydrolics. You cannot compress a liquid. Water in the barrel or snow is a problem. The bullet is a tight fit. The air in front of the bullet will only reach a low pressure even traveling at high speed. inside the barrel. The high pressure is behind the bullet. The water is plastered to the side of the barrel as the bullet passes. this delays the bullet. The pressue of the gas building up multiplies because of this delay. End of barrel.
    What does the oil do in the engine of a car. It actually prevents two moving metal surfaces touching. When the piston moves down after combustion it dous not displace the oil sufficient to allow big end to touch crankshaft. No matter how hard that bullet pushes it will not squeeze past water. The delay is only minute but barrel gives before the water,

  6. #6
    SD Regular willie_gunn's Avatar
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    Through the wonders of the Internet, check this out:

    "air pressure grows so quickly that it reaches the point of shattering the barrel before pushing out the plug"


  7. #7
    SD Regular willie_gunn's Avatar
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    Even more interesting is this article by Charles Babbage, widely recognised as the inventor of the concept of a programmable computer. In 1835 he wrote a book called "On the Economy of Machinery and Manufactures":

    If the muzzle of a gun has accidentally been stuck into the ground, so as to be stopped up with clay, or even with snow, or if it be fired with its muzzle plunged into water, the almost certain result is that it bursts.

    The ultimate cause of these apparently inconsistent effects is, that every force requires Time to produce its effect; and if the time requisite for the elastic vapour within to force out the sides of the barrel, is less than that in which the condensation of the air near the wadding is conveyed in sufficient force to drive the impediment from the muzzle, then the barrel must burst. It sometimes happens that these two forces are so nearly balanced that the barrel only swells; the obstacle giving way before the gun is actually burst.

  8. #8
    Being a daft tw#t I managed to put a bulge in the muzzle of an old .243 BSA CF2. Shooting hinds and the rifles were put in the passenger well of the Landie while we had a quick bite. I didn't think to look for mud and peat from boots in the footwell and the muzzle of my rifle must have taken a great dollop of mud into it. Anyway, I missed an easy 150 yd shot by a long way and the shot sounded very funny...more tinny than usual. I looked at the muzzle and could see mud caked around the foresight....then the penny dropped. Looking down the empty barrel from the muzzle we could see that from the first couple of inches from the muzzle were opened out. I suppose that was lucky. Anyway, had it shortened and it did the job until I broke the rifle and a Pecar scope clambering up a rocky chimney when the leather sling stud gave way - the crappy brass screw studs. Unlucky with BSAs...

  9. #9
    Anyway, had it shortened and it did the job until I broke the rifle clambering up a rocky chimney when the leather sling stud gave way - the crappy brass screw studs. Unlucky with BSAs... [/QUOTE]

    What were you doing? Waiting for Rudolph!

  10. #10
    I used to carry a curtain spring coiled up with the metal bits glued over, then I binned it in favour of taping the muzzle.
    (The Unspeakable In Pursuit Of The Uneatable.) " If I can help, I will help!." Former S.A.C.S. member!

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