What causes recoil on a pcp ?

[ackuric]

"Also, the longer the barrel, the more length/time acceleration of said pellet can affect the gun/you"

That sounds logic. My impact has the 700mm barrel, and the pellet will probably spend longer time in the barrel, as it is also traveling slower, than a .22 rim fire in comparison. So the "push" will last longer.

Valve dwell in part is determined by barrel length. Most pcp's shoot efficiently using 33% or so of their barrel length prior to closing the valve. So a 12" barrel using only 4" of barrel shooting 700 fps will definitely have a shorter duration of recoil than a 24" barrel using 8" of barrel shooting 900 fps. But theres two factors there, Shock factor, and duration factor....shock factor is how much energy is released in that time frame, duration factor is the time frame. So a shorter barrel COULD have a much higher 'shock factor' or recoil, but it would be of shorter duration... Hope this makes sense.

 

[tor47]

Well thanks for the answers, it is not that I need to know, but is is interesting to know

 

[JungleShooter]

Well, thanks, this helps me understand why my PCP pistol at currently 14.5 FPE seems to have more recoil than the bullpup at 31FPE....

Matthias

 

[Eaglebeak]

Well thanks for the answers, it is not that I need to know, but is is interesting to know

I suppose that when you ask a question like that, you are bound to get answers like those above. Another thing that will affect the perceived recoil is simply the weight or mass of the guns concerned. 

 

[mtnGhost]

My Raptor crowned me in the eye about a week ago. I had the reg turned up somewhere around 200bar, and was shooting 66gr ammo. Luckily the SideShot eyepiece was rubberized, but it was a wake up call to its recoil with fat lead in the pipe.

 

[markT]

Try this. Shoot of those cleaning patches that are compressed fiber that weigh little. 

Then fire one of your lead pellets 

Let’s us know what your finding are. 

 

[markT]

Newtons Second Law states that acceleration is produced when a force acts on a mass. The greater the mass (of the object being accelerated), the greater the amount of force needed to accelerate the object (bullet in our case). Everyone inherently knows that heavier objects require more force to move the same distance as lighter objects. The acceleration of our bullets is directly proportional to the amount of force (burning powder) being applied to them and inversely proportional to the mass of the bullet. This means that how fast your gun and bullet accelerate are going to depend directly on the amount of force applied to it, and the weight of the gun or bullet. We now see a clear relationship between force, mass, and acceleration. It is familiarly expressed as Force = Mass x Acceleration, or F=ma.

 

[ackuric]

The formula for recoil energy is E=1/2 MV Squared, with "M" being mass of the gun and "V" being the recoil velocity.





Let us take : M= mass of gun, m = mass of bullet and propellant, speed of gun before firing, u1 = 0, speed of bullet before firing, u2 =0, speed of gun after firing = V and speed of bullet after firing = v.

Applying momentum conservation principle, Mu1 + mu2 =MV +mv

0= MV + mv

V (recoil velocity) = - mv/M


Gun mass, projectile mass (with the mass of air released with it..), and projectile exit velocity are the primary variables which determine recoil velocity, which then allow you to compute recoil energy. HTH

 

[ackuric]

Oh, you want me to formulate?



V = -mv/M

where m = (33.95gr + 12gr) converted to KG is 0.002977

where v = 860 fps converted to M/s is 262.128

where M = 7 lbs converted to KG is 3.175 KG

-0.002977 * 262.128 = -0.780

-.780/3.17 = -.245 M/s or -.8 FPS (Recoil velocity...the negative just shows the direction is opposite of the projectile being fired)



E = 1/2 MV^2

.5 * 3.175 = 1.587

1.587 * -.245 M/S^2 = .09 Joules or .066 ft-lb

So basically, less than .1 FPE is being pushed against my shoulder when I fire my rifle...which makes sense, because its certainly not bruising me up if I fire it 10,000 times.



Calculating recoil impulse or duration however is another formula all together..and IMO using pellet dwell and adding roughly 1ms for the remaining air to expel is a great approach to a simple answer that may not be as exact as the above approach, but 'good enough'. (you would need to know the velocity of air at the muzzles pressure which is quite a complex formula). Using 2/3rd of your terminal velocity such as mine at 860 * .66 = 567. 567 fps / 1000 * 12 = 6.8 inches per ms. My barrel length is 19.5 so 19.5 / 6.8 = 2.8~ ms of pellet dwell inside the barrel (this is extremely approximate) so the pulse duration of my recoil should be roughly ~4ms...



Combining the two formulas above, moving at .8 fps for 4ms would make for roughly .04" of movement..



But there are other formulas you technically have to add to get the total movement of the gun and overall perceived energy felt from recoil, such as the jet energy (residual muzzle pressure leaving barrel, as inefficient shots will have much more 'jet' than efficient)..thats why muzzle brakes help tame recoil in very large bores or powder burners.