Why is rifle recoil so low?

Discussion in 'Weapons, Equipment & Rations' started by Bravo_Bravo, Sep 22, 2011.

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  1. Remembering Newton and his decision to make every action have an equal and opposite reaction, I've long puzzled over recoil.
    Now, hitting a target with SAA will deliver enough kinetic energy to knock a man over.

    So, plenty of KE being delivered at point of impact.

    Now, the round cannot deliver more energy than that imparted to it, which is done when the round is fired.

    Which makes me wonder - how on earth can the energy at impact be sufficient to knock a bloke over, yet the equal and opposite reaction to the round being fired will do no such thing, assuming weapon held correctly?
  2. **** knows but in 1984 when i was a 13yr old cadet firing the .303 it hurt like ****
    • Like Like x 1
  3. Because the body being struck isn't a spring like the one in the rifle used to absorb and redirect the energy imparted to drive the bolt back forward?
    • Like Like x 2
  4. Men fall down when shot they don't get knocked over..

    Get back to your ******* action flicks you throbber
    • Like Like x 7
  5. It's because of a number of things. First, Kinetic energy is derived from velocity and mass; a weapon weighs a lot more than a round so to balance both sides of the equation, the weapon can't move very fast. Weapons can also have springs behind the working parts, so that extra energy absorbed there as well. The person firing the weapon also absorbs energy from the weapon.
  6. So people just fall downwards with no backwards movement, thicko?

    What are you doing up this late on a school night?

    Why not, dunno, **** off maybe?
  7. FDW

    FDW Old-Salt

  8. Sure, but a body weighs a lot more than a round and ( unless you are as thick as thegimp) will be moved backwards on impact. Implication from your comment is that by bracing yourself while wearing Osprey, you'll only have as much KE delivered at impact as at the shoulder of the firer.

    Springs behind the working parts are not to reduce recoil but to cycle the working parts.
  9. FDW

    FDW Old-Salt

    I've hit a deer with a .308 and the ****** didn't move.

    I mean it dropped dead about 3 seconds later but physically it wasn't moved
  10. FDW

    FDW Old-Salt

    Yeah but that's going to absorb energy no matter whether thats its purpose or not.

    if you fire a sten on full auto there's very little recoil because of the big lump of a bolt sliding back and forth.
  11. Good point; went on a stalk with a telly chef last year; bagged two deer neither of which moved much, but I did see signs of cavitation and hydrostatic shock. Heavy buggers.
  12. Bravo Bravo, since when do men get knocked over when shot with small arms projectiles?

    Anyway, energy is irrelevant in this discussion, since KE is not conserved and may be transformed into other forms of energy, such as heat. Linear momentum is conserved, however measured in kg*m/s. According to wikipedia, the projectile from an SS109 round weighs 0.004g and leaves the barrel travelling at 940 m/s, giving a momentum of 3.76 kg*m/s. Were all this momentum imparted to a lightly built woman, weighing 50kg, she would be pushed back with a velocity of 0.0752 m/s. 7.2 centimetres per second. That's not very fast, never minding all the assumptions like it being a small woman and there being no drop in muzzle velocity, and momentum being instantaneously transferredd. Small arms fire does not 'knock' people over. Thankfully I have no personal experience of the matter but, hazarding a guess, being shot is painful and disorientating, which may cause the victim to fall down. A bit like being told Mo Mowlam is coming over for strip poker.

    Springs do not soften recoil by absorbing energy, they do it by increasing the time over which momentum is transferred to the firer - much like a crash helmet increases the collision time - and therefore forces on your head from rapid deceleration - by providing cushioning foam between your head and the road.

    Momentum is always conserved, you cannot get rid of the rifle's backward momentum without sending something else back. Recoilless rifles do this by having the backblast gases's backward momentum equal the projectile's forward one. Muzzle brakes on ****-off big 50cal rifles are often pointed backwards to direct some of the muzzle blast that way, at the cost of hurting people sitting next to the rifle.

  13. The principle you are grasping for is the conservation of momentum. While the round goes pinging off, some of the energy going the other way is spent in driving the working parts back and chambering a new round, but fundamentally speaking, a 5.56 round won't knock a man back/over.

    Also consider the difference between being struck by something while adopting a braced supporting position versus being caught unawares - which is more likely to make you move?
  14. Sorry, don't have a scoobies how you derived that implication?
  15. Bellend. Despite the fact that the ******* spring cycles the round, does not mean that on account of the thing moving backwards very fast carrying a lump of metal with it that it does not absorb the initial shock. Which it does.

    And people don't fly backwards superman style, they tend to fall over on account of a small and light bit of metal whacking right through them, hurting or killing them. I would expect that if they were to wear armour, that they would be more prone to be pushed over by the KE smacking into an immovable surface than if it went through them.

    Ho hum.

    PS I'm pisse so ignore me, but your tone pissed me off when the replies you had seemed fairly logical.