sniper rifle questions.
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It does answer part of the question. I had failed to take into account the reaction from the release of the gas from the opening of the barrel as a contribution to the felt "recoil".Originally posted by Meia Gisborn:(Not Dave here, but....)
Short answer: on the AR15/M16, recoil isn't felt until the projectile exits the barrel.
Long answer: when the cartridge is ignited, the propellant combusts rapidly. The gas expands and pushes equally in all directions, but it hasn't been vented yet. When the projectile passes the gas port, some of the expanding gas is directed through the port and into the gas tube to push the bolt carrier back and begin unlocking the bolt. At this point, there is still no felt recoil as the expanding gas has not been vented out of the closed system yet. As the projectile exits the barrel, the expanding gas is vented out the muzzle and the bolt carrier, with the bolt now unlocked, is driven by gas pressure back against the recoil spring in the buffer tube. The recoil felt by the shooter is thus a combination of the expanding gas escaping at the muzzle and bolt carrier's rearward travel.
Does that answer your question?
But there is a point of contention here; you mentioned that until the round leaves the barrel, the system is considered a closed system and therefore due to the expansion of the gas pushing equally in all directions, no recoil should be felt. However, taking into account the change in mass distribution of the so called "closed-system" occurring from combustion to projectile just leaving the barrel, with the change in distribution primarily brought about by the travelling of the projectile from chamber to the mouth of the barrel, to reconcile the equation, there must exist a reaction in direct contrast with the direction of travel of the projectile, which forms the basis of my query. May I be so bold as to say that the closed system theory, in order to work, must take body of the firer into account for both sides of the equation to ....... equate.
To put it simply: if the projectile moves forward, something must be moving backwards as a reaction, and if the bolt and the bolt carrier or not moving backwards, what is? -
my understanding is the reaction is being transform to other means..... that the lock up of the rifle gives the chamber and barrel close when the roiund is fired! the reaction is that the extra gas i being channel thru the gas tube...the solid lockup thus making the path of least resistance and that is being change to hot gas pushing thru the gas tubes! the delay gives the round ample time to leave the barrel and thus not affact the accuracy..
felt recoil is usually an after-effect after the round has already leave the rifle ! the gas movement piushing the bolt carrier in this case the M16, or the gas pushing the piston on the AK of FAL!
DaveC -
That's what I initially thought too, until a member of our shooting club who was a ballistician at Federal Arms explained that, as the projectile spiraled down the bore, it was still firmly in contact with the barrel and pulling it forward, along with the rest of the firearm. This forward force cancels out the opposing reaction caused by the expanding gases pressing the base of the case against the breechface.Originally posted by crosshairs:To put it simply: if the projectile moves forward, something must be moving backwards as a reaction, and if the bolt and the bolt carrier or not moving backwards, what is? -
I've never thought of it that way before.....
But something just doesn't add up.
Let me go grind some grey matter..... -
Ok, I've done a little mental simulation of the firing sequence and I have come up with nothing.
However, going back to the basics of transfer of momentum, there has to be a recoil felt even before the round has left the barrel. In fact, it should have started the moment it left the cartridge. So somehow the force exerted on the barrel by the projectile has already been accounted for without "stealing" from the recoil.
Think about this: A mass has shifted its position. This shift has to be matched by an equal and opposite shift in terms of momentum.
Lets say the projectile weighs 10g(0.01kg), the rifle weighs 10,000g(10kg)
Let's say that the muzzel velocity at the opening of the barrel is 300m per sec
That will give us 0.01 x 300 = 3KGM/Sec
That mean the rifle must be reacting with a speed of 10/3 = 3.3M/sec
In this calculation, the barrel's forward moving component must have already been accounted for by the very speed achieved by the projectile at the end, for if the round failed to make contact with the wall of the barrel, it would have been a much higher muzzle velocity, resulting in a much higher reacting speed by the rifle.
I'm not trying to find fault with a specialist in the field of balistics but the very basics of physics suggests a discrepancy here. -
Another point to note. By the argument put forward by you that no recoil occurs before the round leaves the barrel, or that all reaction is balanced out by the contact between barrel wall and projectile, then we are left to explain one very obvious characteristic of a firearm.
Weapon Jump. When the barrel tilts upwards after firing a shot. The effect is more pronounced when a rifle is not held down firmly.
I used to shoot with a rifle sling. I compared the grouping shot with a sling to another set of grouping shot without the sling. At 300m away the difference can be as much as 2 feet.
If the weapon does not recoil when the round is in the barrel, how does one explain the 2 different groupings, a result of difference in the suppression of weapon jump? -
I'm not a ballistician and am consequently not familiar with the hard physics behind firearm recoil. However, take a look at the high-speed research videos of various firearms being shot in this website. It appears that, in all cases, there is no visible recoil or muzzle lift until the projectile has exited the barrel. There are probably other factors at work here that neither of us is aware of. I'll certainly float the question by the ballistician the next time I bump into him at the club range, as I must admit to being further intrigued by all this!
However:...for if the round failed to make contact with the wall of the barrel, it would have been a much higher muzzle velocity, resulting in a much higher reacting speed by the rifle.
Actually, the opposite is true. If a projectile is not in contact with the barrel and doesn't form a perfect gas seal within the bore, some of the expanding gases from the burning propellent will be vented around and ahead of the advancing projectile, instead of propelling the projectile. The resulting muzzle velocity will therefore be lower, not higher. Just ask any shooter who has accidentally fired a 9mm or 357Sig cartridge in a 40S&W firearm.
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I think I can answer to this if you are shoooting your M16S1! unless you re doing SAR21! THE m16s1 HAS an inherit flaw whereby your sling attachemnt is pivoting onto the barrel end ! thus when you pull with your sling tight! it actually changes the harmonics of the barrel and thus change your point of impact ! this probem is solve when we went with a free floating handguard which completely removing the delta ring and thus eliminating this issue!Originally posted by crosshairs:Another point to note. By the argument put forward by you that no recoil occurs before the round leaves the barrel, or that all reaction is balanced out by the contact between barrel wall and projectile, then we are left to explain one very obvious characteristic of a firearm.
Weapon Jump. When the barrel tilts upwards after firing a shot. The effect is more pronounced when a rifle is not held down firmly.
I used to shoot with a rifle sling. I compared the grouping shot with a sling to another set of grouping shot without the sling. At 300m away the difference can be as much as 2 feet.
If the weapon does not recoil when the round is in the barrel, how does one explain the 2 different groupings, a result of difference in the suppression of weapon jump?
DAveC