recoil

[cliffe]

why would say a .308 have less recoil than a 30-06 shooting the same bullet at the same speed in identical rifles, both weight and barrel length. i know the 06 is burning more powder, but how does that relate to kick if the speed is the same??? happy holidays, cliffe

 

[Akbushape]

Cliffe,
I'm no expert by any means but I can't see how the recoil
would be any different, It should be the same in both rifles.
If you push say a 180 gr bullet out at say 2800 fps the kinetic
energy required to do that is going to be a constant. With the
the two rifles weighing the same and all aspects of the rifles
the same, then the recoil would have to be the same. Seems any
percieved difference would be a figment of the imagination.
But what the hay, maybe the case size contributes some how but I
don't see how it would. Some technocrat somewhere has probably
measured it with a scale. Maybe someone will enlighten us.
Possibly even more than we care to be enlightened
Good question though.

 

[6BRonwheels]

Hi,
The basic answer to your question about recoil is that the more powder that you burn, the more recoil energy is produced. If you are using 10 more grains of the same powder to propel the bullet at the same speed, the extra thrust from the ten extra grains ends up in about 2 pounds of extra recoil,wasted energy).
In a way it is like comparing an incandescent bulb to a florescent bulb. The bulb that consumes more electricity to operate, will also creates more heat,wasted energy).

 

[Twud]

Where did you come up with 2 guns that are exactly the same?

 

[gunsandgunsmithing]

Two words--"Efficiency" and "Air"
What some people don't consider when attempting to apply Newtons law of motion to guns is "air". About 80% of felt recoil from a gun is from air. The blast from the muzzle and the resistance the air has against it generates the vast majority of the recoil. A more efficient cartridge can do the same or more with less powder, creating less muzzle blast, moving less air.
This is why a muzzle brake works so well at reducing recoil.

---Mike Ezell

 

[cliffe]

twud, i did it using mirrors seriously, say i use 2 savage 110's one a 308 and an 06, both long action and same barrel length, hows that twud, now say i shoot a 150 grain using varget the 06 uses about 3 grains more powder to go the same speed, but if it is going the same speed how can it kick more?
i understand it would kick more with a larger amount of powder that would increase speed beyond what the 308 can do... cliffe

 

[Toby Bradshaw]

Think of it this way. Without any bullet at all, which of the following will produce the most recoil? Apply Newton's third law of motion,which follows from the conservation of momentum, mass*velocity). For the sake of comparison, assume the propellant in each case is completely burned,which, in reality, it would not be unless there is a bullet to keep the pressure up) and that the gases are moving the same speed in each case.

.308 47gr H4895
.30-06 51gr H4895

Both of these loads give about 2900fps with a 150gr bullet, according to the Nosler manual.

Toby Bradshaw
baywingdb@comcast.net

 

[Cheechako]

I think it's a simple matter of ten grains more powder. A 150 grain bullet in a 308 would become a 160 grain bullet in an '06. Both the burned and unburned powder make up a 10 grain additional mass that is ejected along with the bullet. A 7% increse in bullet weight is probably noticable in felt recoil.

But, what do I know?

JMHO

Ray

 

[Toby Bradshaw]

It's not as simple as the difference in propellant weight, because the propellant gases move much faster than the bullet once the bullet leaves the muzzle. This means that a grain of powder produces more recoil than a grain of bullet weight.

Toby Bradshaw
baywingdb@comcast.net

 

[gunsandgunsmithing]

This isn't all that difficult although it's widely misunderstood. Gunsandgunsmithing has the right idea although is has nothing to do with air. Secondary recoil would also occur in a vacuum.

I assume that it would do so in a vacuum because of the expanding gases produced by the burning powder.
We, or I don't shoot my guns in a vacuum. And although it may not be enough difference to feel, wouldn't a gun recoil harder in cold dense air than in warmer air?---Mike Ezell

 

[gunsandgunsmithing]

Cheechako, I'm not a physicist but the gases will exit faster than the bullet. They are what is producing the accelleration of the bullet after all. Now if they totally quit making pressure before bullet exit, that'd probably be a different story. Once the bullet clears the muzzle, the gasses exit without nearly the restriction on them that the bullet makes. Ihope that helps.---Mike Ezell
p.s.--The best way for me to describe this is to just look at how effective a brake is at reducing recoil. The bullet is still holdig back the gasses to some degree as long as it is still in the brake. The gasses are exiting basically unrestricted through the holes in the brake.If air was not a factor in recoil, a brake would do nothing to reduce the recoil

 

[Toby Bradshaw]

Hi Ray. Well, quite a few things in physics are counterintuitive. Who would guess that a clock runs faster at the top of a mountain than at the bottom?

But I don't find the greater speed of escaping gas relative to bullet counterintuitive at all. The only reason the gas is going as slow as the bullet when both are in the barrel is that the bullet is getting in the way! Once the bullet is out of the way,when it exits the muzzle) the escaping gas speeds by the bullet. Collision between the escaping gas and the molecules of air outside the barrel means that the expanding gas won't "pass" the bullet for long, though.

Toby Bradshaw
baywingdb@comcast.net

 

[Cheechako]

I hit the wrong button and deleted my last post when I meant to edit it. For those that didn't see it, I said I was dubious.

Toby and Mike have convinced me that I was, uhhh, wrong. The gasses exiting the barrel do play a role in recoil. The muzzle brake example convinced me. I use a muzzle brake on a couple of my rifles and can see where re-directing the gasses before they leave the barrel does soften recoil.

Is there any way to measure the effect that, say, 10 more grains of powder would have?

Ray

 

[gunsandgunsmithing]

Maybe muzzle pressure as indicated by a Pressure TrAce or other means of checking pressure while the bullet is still in the barrel would be at least indicative. Slower powders wil generall make a brake more effective. They should also make more muzzle blast and more recoil to some degree without a brake. I put on an avg. of 175 brakes a year and also play with some wildcats to hopefully maximize cartride efficiency. That probaly opened my eyes to this as much as anything else. My 30 Major,grendel) has noticeably less recoil than a 30BR using the same weight bullet and at the same velocity.Why? A more efficient case using faster powders creating less muzzle blast,and displacing less air.:idea:---Mike Ezell

 

[gunsandgunsmithing]

We, or I don't shoot my guns in a vacuum. And although it may not be enough difference to feel, wouldn't a gun recoil harder in cold dense air than in warmer air?

The pressure in the barrel, even with 100% combustion, will still be in the thousands of PSI when the bullet exits. Atmospheric pressure, despite variations in temperature, will be very close to 15 PSI,one atmosphere, 30" of mercury, 760 millibars, however you want to represent it). The only significance air has is the 15 PSI pushing on the pointy end of the bullet in the barrel vs the combustion gases in thousands of PSI pushing on the other end.

That 15 PSI is pretty constant regardless of air temperature. It does vary slightly, less than 10%, between hurricane weather and a bright sunny day. Theoretically at least, recoil should be slightly higher in a hurricane when the barometer says 13.5 PSI. The same is true of high altitudes vs sea level. That 1.5 PSI atmospheric difference gets lost quickly when compared to the pressure on the base of the bullet which is in the thousands of PSI. I seriously doubt that it would be possible to measure the difference in recoil between a rifle fired at sea level on a sunny day and the same rifle fired atop Mt. Everest in a hurricane.

If air was not a factor in recoil, a brake would do nothing to reduce the recoil

Sorry but that's incorrect. A brake gives escaping gases an exit other than through the end of the muzzle. The more gas that gets bled off perpendicular to the barrel axis the less there is to generate thrust,secondary recoil). If you want a really effective brake, angle the ports more toward the butt of the rifle similar to those on some 50 BMG's. The force then is partly directed back from the muzzle which partially counteracts the thrust from gases exiting the muzzle. But please don't use the bench next to me.

Air has nothing to do with how a muzzle brake works. A muzzle brake would work just fine in a vacuum,I know, you don't shoot your gun in a vacuum but many physics examples use a vacuum as a standard reference - then things like air temperature don't confuse people). Plus, you wouldn't be able to hear the ungodly noise since sound waves require a medium to travel through.

Sorry gunamonth, while I respect your opinions, you are the one who is wrong this time. First of all, the pointy end of the bullet has virtually zero to do with this whatsoever and the same can be said for atmospheric pressure. It's the expanding gasses that propel the bullet down the bore and the don't come to an abrupt halt when the bullet leaves the muzzle. They continue to push forward against the air. This in turn makes for a substantial percentage of the guns rearward movement. Are you saying that the same forces that propel the bullet down the barrel don't push the air out in front of the gun?
As to the muzzle brake...the gasses are simply being redirected....instead of pushing the gun rearward due to the resistance of the air...the gasses are forced laterally in equal and opposing directions thereby greatly reducing the amount of propelling gasses forward...against air. That's all that there is for them to push against once the bullet clears the muzzle! As to the vacuum....I don't know but I doubt that when smokeless powder is used as the propellant, the expanding of the gasses from the burning powder whould have to affect that "vacuum status". You just created thousands of psi in pressure in an instant. I won't argue the vacuum thing much because I simply don't know, but air is a significant factor in recoil and recoil control---Mike Ezell

 

[Toby Bradshaw]

Got to side with gunamonth on this one. You're right that the propellant gases are pushing against the air, but all that does is raise the temp of the air,makes the air molecules move faster from collisions with propellant molecules). As gunamonth says, pushing against the air doesn't do a thing to increase recoil.

Think of the propellant gases as rocket exhaust. Does a rocket motor produce more thrust in air than in space? No. A rocket motor doesn't work by pushing against air -- it works by throwing mass out the nozzle at high velocity, and conservation of momentum means that momentum of the rocket body is equal and opposite to the momentum of the exhaust.

A muzzle brake works by redirecting the velocity vector of the propellant gases,momentum is a vector quantity). As mentioned, if you turn the gases around 180 degrees,with no loss of energy), pointing them back towards the shooter, you could eliminate the recoil produced by the gases and offset some of the recoil produced by the bullet. Basically you'd be making your rifle into a rocket trying to fly away from you,even in a vacuum), while the recoil from the bullet is pushing in the other direction.

Toby Bradshaw
baywingdb@comcast.net

 

[gunsandgunsmithing]

Got to side with gunamonth on this one. You're right that the propellant gases are pushing against the air, but all that does is raise the temp of the air,makes the air molecules move faster from collisions with propellant molecules). As gunamonth says, pushing against the air doesn't do a thing to increase recoil.

Think of the propellant gases as rocket exhaust. Does a rocket motor produce more thrust in air than in space? No. A rocket motor doesn't work by pushing against air -- it works by throwing mass out the nozzle at high velocity, and conservation of momentum means that momentum of the rocket body is equal and opposite to the momentum of the exhaust.

A muzzle brake works by redirecting the velocity vector of the propellant gases,momentum is a vector quantity). As mentioned, if you turn the gases around 180 degrees,with no loss of energy), pointing them back towards the shooter, you could eliminate the recoil produced by the gases and offset some of the recoil produced by the bullet. Basically you'd be making your rifle into a rocket trying to fly away from you,even in a vacuum), while the recoil from the bullet is pushing in the other direction.

Toby Bradshaw
baywingdb@comcast.net

O.k. This is getting pretty techhy but I want to see what I'm missing here,so here goes...

You're right that the propellant gases are pushing against the air, but all that does is raise the temp of the air,makes the air molecules move faster from collisions with propellant molecules). As gunamonth says, pushing against the air doesn't do a thing to increase recoil.

Think of the propellant gases as rocket exhaust. Does a rocket motor produce more thrust in air than in space? No. A rocket motor doesn't work by pushing against air -- it works by throwing mass out the nozzle at high velocity, and conservation of momentum means that momentum of the rocket body is equal and opposite to the momentum of the exhaust.

A muzzle brake works by redirecting the velocity vector of the propellant gases,momentum is a vector quantity). As mentioned, if you turn the gases around 180 degrees,with no loss of energy), pointing them back towards the shooter, you could eliminate the recoil produced by the gases and offset some of the recoil produced by the bullet. Basically you'd be making your rifle into a rocket trying to fly away from you,even in a vacuum), while the recoil from the bullet is pushing in the other direction.

So by heating the air molecules you create thrust? That being the case, I can see where the gun would still thrust rearward in a vacuum. How is that different than taking the hose from your air compressor and blasting air from it into the atmosphere? It creates thrust as well. Idon't really care that the thrust is from heated molecules or not. The gun does come backward due to thrust created by a forceful blast of gasses or air forward...Mass against mass.Correct?---Mike Ezell

 

[Toby Bradshaw]

Hi Mike. You aren't producing thrust by heating air molecules outside the barrel with the gases from the burning propellant -- that heat is just wasted energy,"wasted" because it doesn't make the bullet go faster).

Thrust is produced by ejecting mass with some velocity. If you stood on a flatbed railcar covered with rocks and started throwing the rocks as hard as you could off the back end, you would produce thrust that moved the railcar forward,assuming negligible friction on the rails, etc.). To produce more thrust you could throw more rocks per unit time, throw them harder,more velocity), or throw bigger rocks,more mass) at the same speed. In any case, the momentum of the rocks,mass * velocity) is pointed in the negative direction,behind you), and the railcar,with you on it) moves with an equal and opposite momentum -- forward. As far as the railcar momentum is concerned, it doesn't matter whether you're throwing the rocks in air or in a vacuum. If in air, the friction between the rocks and air raises the temperature of the air and robs the rock of its velocity -- momentum is transferred from the rocks to the air molecules, but total sytem momentum is still conserved. In a vacuum the rocks go a lot farther before transferring their momentum to the ground, but the effect on the railcar momentum is the same as in air.

A rifle produces thrust in two ways -- by throwing a bullet out the end of the barrel, and by throwing a mass of hot propellant gas out the end of the barrel. You feel the thrust as recoil. Momentum is conserved -- the mass*velocity of the bullet+gas is exactly matched by the mass*velocity of the rifle as it recoils. Just before the bullet leaves the muzzle you can fairly easily calculate the momentum of the bullet and gas -- multiply their weight by their speed,and assume that the gas is moving the same speed as the bullet). Once the bullet leaves the muzzle the gas can accelerate to a greater speed, and this additional momentum produces secondary recoil,which you don't really notice because it happens so quickly after primary recoil).

We don't want to change the direction of the bullet -- we want it to go downrange, so some thrust,recoil) is unavoidable. But the thrust from the propellant gas can be diverted,by a muzzle brake) so that it doesn't go downrange -- it's momentum vector is some direction other than straight away, and any direction other than straight away reduces momentum in the direction of your shoulder,though total momentum must be conserved). The most effective recoil-reducing direction,and, unfortunately, the one that produces the most noise) is to turn the gases right back at you.

That's why cartridges with big powder charges behind light bullets benefit most when a muzzle brake is used -- the more thrust produced by the propellant, and the less thrust produced by the bullet, the more effective,in terms of percent recoil reduction) the brake can be.

Toby Bradshaw
baywingdb@comcast.net

 

[gunsandgunsmithing]

Alright. I stand corrected. If I understand this right, the whole point of argument here was that it is the propulsion gases alone,not air or it's resistance) that are creating the rearward thrust of the gun.,conservation momentum). And a brake is simply redirecting said gasses..Is that what I have been missing all along?---Mike Ezell

 

[Toby Bradshaw]

..Is that what I have been missing all along?---Mike Ezell

Yep. Glad it makes sense now.

Toby Bradshaw
baywingdb@comcast.net