Canadian Airgun Forum

Request for direction from the PCP knowledgeable.

On a regulated gun, I'm trying to understand tune adjustments for low velocity (650-ft/s) high efficiency/shot count.
Would lowering the regulator pressure and lowering hammer spring tension be the path to take?
I also read of chokers, power adjuster screw, which if I read correctly is the transfer port adjustment?
Does the power adjuster/transfer port have to be lowered as well to get low velocity or can it be achieved with regulator adjustment and hammer spring adjustment, leaving transfer port high power?

I'm new.
Am I even making sense asking questions..lol

Understanding PCP for an old guy is like home school learn on your own...
Trying to put together PCP puzzle.

If the rifle has a transfer port adjustment, a balance between hammer tension, port opening and regulator pressure will give the best shot count at low velocity.
Example, simply reducing the regulator pressure and port opening on my FX but leaving the hammer spring almost at maximum, my shot count went from 46 at maximum power to 151
at reduced speed. I did not chronograph the rifle, but it was shooting 1/8" to 1/4" groups at 50 feet, rapid fire with a variety of pellets.
Had I reduced the spring tension on the hammer, the count would have gone up again.

_________________
Best Wishes
Daryl

On my Gauntlet there is no port choke or hammer adjuster, but by lowering the reg PSI I was able to bring it down 620 fps from 820 for ratting. There was an increase in count but never tracked.

An internal reg is by far the hardest way to adjust the velocity as you need to degas the gun and remove the cap on the tube each time. Very small increments on the reg adjuster will be a major change in pressure. If you install the reg yourself then you can record the orientation of the reg upon installation and a sketch of the face or side marks to help adjust later. On a reg with front facing marks you are able to look down the tube and see the reg rotation and the hash marks.

My Crosman Icon only has the hammer spring adjuster. Only a few turns back on the adjuster will mean that the valve will not open at full pressure. To make the gun basement friendly I use an external reg tank and a remote hose.

Have a great day
Robert

Thanks Daryl.

My take is adjusting the transfer port only can give the reduced velocity but not efficiency.
I'm guessing the transfer port is slowing flow rate pushing pellet, not shot volume, possibly wasting air after pellet has exited barrel?

Yeah, I believe so...

Actually just keep a general idea in mind, less air equal to slower velocity.

Adjusting the speed is easy. Just following the instruction even just the guide from the factory can make it. And either the 3 things you can turn on the gun can do it.

Getting a good efficiency is another part. It's not complicated but need a lot of patient to do the tuning, record making, experiments...

While all done, you can have the max shot count with quietest report from muzzle then still keep the highest velocity you desired...

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[quote="YepYep"][quote="canadaman30"]

Actually just keep a general idea in mind, less air equal to slower velocity.



Thanks YepYep.

This all helps. From limited research my initial thoughts was to start with a lower regulator pressure and lowering hammer spring, for less air volume lower velocity, higher efficiency. If the transfer port choker only restricts overall flow I'm guessing using only the choker to reduce velocity will not benefit shot count efficiency, only lowering the flow to push pellet but still using expelling wasted air volume after the pellet exits muzzle?

Higher regulator pressure will be quieter and usually result in more shots per amount of air used, but you can't take the tank pressure as low so total shot count is not as high.

I'm not understanding that first part of your statement, grantmac about higher regulator pressure being quieter. Yes to the shot count as cannot run tank lower than the regulator setting.
Well, you could run it lower, but FX says damage might result.
With my FX, reducing the regulator pressure from 135 to 100 bar (+ reducing the port), increased my shot count x 3 times.
Just reducing the port, but leaving the regulator at 135, did increase the shot count but not by much = wasted air.
I tabulated all this in a thread on the FX Dreamline. Can't quite remember all the exact numbers now, except for reducing the regulator pressure and the port, increased shot count
from 46? to 151. The reduction also made it quieter as less air was discharged, I assume.

_________________
Best Wishes
Daryl

I did not know that.
Another consideration for neighbor friendly low noise backyard target shooting.
Patiently waiting for warmer weather to get out to play..

Thanks Daryl

Your information has answered and confirmed some unanswered questions. Much appreciated info I can reference from.

To me, that just doesn't make sense. Higher volume of air quantity & pressure developing higher velocity being quieter? To me, doesn't make compute.

_________________
Best Wishes
Daryl

In my experience this is only true if your hammer spring preload was excessive to begin with.

If the reg pressure is low and hammer spring is too strong then the valve open time will be very long. And this will create a obnoxious bark when the gun fires, and waste air.

Raising reg pressure will make the valve harder to open,, therefore reducing valve open period. This could help with reducing noise. I experienced this on my Steyr LP2. The gun was shooting 300fps and was unbelievably loud. It was getting 20 shots per fill. Turns out that the reg was badly adjusted (pressure much too low). Previous owner was trying to increase the pressure by increasing hammer preload.

The ideal case for low velocity and efficient airgun is relatively low reg pressure and matching low hammer preload. This will maximize air usage since your reg will keep working until lower pressure. Transfer port size also affects power and shot counts: smaller TP = lower velocity and higher shot counts. Although I don't really know the relationship between efficiency and transfer port size.

I'm saying if you drop the velocity by either reducing hammer spring and/or reducing TP size the rifle will be quieter compared to the same rifle at that velocity with a lower reg pressure.
This is because the valve is open for a much shorter amount of time.

My experience across several platforms anyway.

Doesn't make sense to me either... Barrel length, yes. Sleeved barrel, yes. Lower velocity, yes...

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OP, think of a PCP as a carburetor.
- You want more HP/speed, you'll need more air (or gas).

Your hammer spring/valves and other adjustments, are you carb jets, needles and air-fuel adjustments...
- You need to find the right balance.

The regulator, that's like your fuel pump. Your air tank can be filled to +200 bars
- If you're into higher speed (for heavier pellets), 85 bars probably won't cut it, you might want something that will constantly deliver 100 bars or 110 bars of pressure... Just just a 4psi fuel pump won't cut when feeding a high performance engine

I'm kinda seeing it, but not totally. Makes my old head hurt.

_________________
Best Wishes
Daryl