Relationship between barrel length and working pressure.

[Arash]

Hi.
As I know (in regulated pcp) if we want shorter barrel we have to increase working pressure and longer barrel can achieve that velocity with less pressure.
So what is relation between this two to get the best accuracy? If I set regulator on low pressure pellet won't accelerate enough in barrel and each vibration in gun change the direction. If I set it at high pressure after pellet leave the barrel air behind it will make the pellet to vowel.
thanks.

 

[cernunnos]

Speed of pellet say 300 meters/second; speed of sound in steel (speed of vibration) about 5 kilometers/sec; speed of sound in air about 343 m/sec. 

The pellets will never outrun the vibrations (300<5000).

Assuming the pellet skirt is even and the barrel crown is even, and flow at exit is laminar (smooth), no upsetting forces at muzzle. But just in past the muzzle, the air can over-run the pellet (343>300) and is no longer laminar. This can cause turbulence in front of the pellet. This points out the virtues of an air stripper or something that acts as such, like an ldc.

More to the point, stiffness of a uniform solid is roughly proportional to the cube of the length. So, if a barrel is twice as long, it will bend about 8 times as much under the same force. A barrel 3 times as long will bend 27 times as much. This is the real downfall of long barrels.

Barrels for accuracy are on the stout side (stiffer per unit length), and have shortened since the late 1800s. Don't sweat the loss of air effeciency.

 

[Arash]

I don't have any problem with harmonic vibration in barrel because it is not a flattering barrel. So it's pretty solid. (My gun is cricket)
When I said vibration I meant hand shake and move backward when I pull the trigger. So if the pellet leave the barrel sooner and moderator do the air stripper it can overcome both turbulent behind it and barrel movement. I don't want to hit supersonic speed.
In full length rifle I hardly noticed any movement when I was shooting but with this one when I pull the trigger the barrel turning upward.

 

[John "spysir" Blount]

Well............. ..


How about I call it " muzzle flip" , see it a lot in FT rifles with very short barrel shooting full power ( 20fpe in the U.S.).
The barrel does "flip" up when fired. Now I've heard different ideas of exactly why but........ . A good quality muzzle break - with air stripping qualities also- might be exactly what your looking for.

From a Vanquish that has "blast" - air over running pellet- inside shroud pushing the pellet around after it left the barrel, this fixed it.

I think rowen sells some strippers/breals in the ULK? 


John

 

[cernunnos]

Yeah, this sounds like muzzle flip. The root cause is that the pellet acceleration forwards accelerates the barrel backwards. The resistance to moving backward is applied at the buttpad, below the line of the barrel. The force backwards at the barrel and the force forward in line with the buttpad yield a spin force centered between the two. The resistance to spinning is from your grip and the angular inertia of the gun around the spin axis. Angular inertia is determined by mass times the distance from the center.

Some solutions:
Add weight to the ends of the gun
Make the gun longer
Bring the barrel more in line with the shoulder pad
Add an air stripper that both adds weight to the end, and catches the force of the exhausting air to partially counterballace the bullet thrust.