pellet weight vs effiency

[Whatsquirrel]

When it comes to pellet weight is there any advantage in using lighter pellets or heavier pellet to increase efficiency? This just for punching paper. Trying to get the most shot count out of my new syn rod .177. I was thinking if there was a difference I could tune it to the fps range with the pellet that would be more efficient. Say cphp vs cpum.

[PakProtector]

within reason, heavier is both more efficient, and has higher BC to buck the wind better. If that more efficient pellet is happy with the barrel is quite another story.
cheers,
Douglas

[SpiralGroove]

Hey Whatsquirrel,
Pellet weight by definition does not determine PCP efficiency.  At a given velocity, heavier pellets transfer more energy downrange, creating more FPE vs. lighter pellets.  PCP efficiency is increased by optimizing valve airflow given a pellets weight and desired pellet velocity.

Method:
Grab some JSB pellets in 8.4, 10.34 and 13.4 grain.  Find the pellet which shoots best at your desired velocity.  Then tune the gun for max. efficiency given the pellet choice and velocity.  Efficiency without accuracy is a waste of time.

In my example, for punching paper you probably will use either the 8.4 or 10.34 grain.

My Two Cents...........

[rsterne]

Accuracy is everything, so use the pellets that produce the tightest groups.... Generally, without any adjustments to the gun, heavier pellets are more efficient as they create more energy from a given amount of air released by the valve.... However, for punching paper you don't need much energy, so you can detune the gun to use lighter pellets (assuming they are accurate in your gun).... Since overall, the less FPE you generate the less air you should use, you should be able to tune the gun for a greater shot count with lighter pellets....

So, heavier pellets should be the most "efficient".... but lighter pellets should allow you (with proper tuning) to get the highest shot count for a given velocity....

Bob

[SpiralGroove]

Hey Doug & Bob,
My (limited) perspective of PCP efficiency was "not wasting air" (blowing it out the barrel or leaving gaps for unwanted air expansion within the valve) at a given pellet weight & velocity.  However, your assuming this is a "Given" and looking at the bigger picture of basic energy transfer - Right?

Kirk

[rsterne]

Correct.... PCP efficiency, at the primary level, is governed by how far down the barrel the pellet is when the valve closes.... The length of time the valve is open (dwell) at a given pressure is governed by the hammer strike.... If the valve is open too long, you waste air.... With heavier pellets, they accelerate slower, so for a given valve dwell (air pressure / hammer strike combination) the valve closes before the pellet has moved as far, and efficiency (in terms of FPE/CI of air used) is higher....

If you use a lighter pellet and then reduce the hammer strike so that the muzzle velocity is the same as it was with a heavier pellet, the valve now closes at the same point in the barrel as with the heavier pellet, roughly matching the efficiency (in FPE/CI).... However, since the FPE of the lighter pellet is less, that means you use less air per shot (because you have reduced the valve dwell).... This will give you more shots per fill....

Bob

[SpiralGroove]

Bob,
Thanks for breaking it down to the basics
Now I Know how my daughter feels when I help her on Algebra homework
Kirk