Is my methodology to calculate the "sweet spot" right?

[charlesdias]

For unregulated PCPs I use the following methodology to find the (in)famous "sweet spot":

1 - Fill it up the tank to the maximum pressure indicated by the maker;

2 - Start shooting 10 pellets rounds through the chronography taking not of the speeds;

3 - After each round I take note of the remaining pressure in the the tank;

4 - I stop shooting around 80 BAR;

5 - I find out the best speed for the kind of shooting I intent with the gun and start substracting all other speeds from it like:

Best speed - speed 1 = spreed 1

Best speed - speed 2 = speed 2

6 - After doing that for all speed I took note I consider the "sweet spot" the interval of pressure on the tank that gave me a spreed of maximum 40 FPS.

Is this methodology right?

[Ribbonstone]

Pretty much the method I use, although usually will shoot a second string  of shots more closely centered on my suspected sweet spot (from the first tests).

I usually sty inside of 3% of the max recorded shot, but 4% will work.

So here I shot a long string while setting up a AAs200 .22 to be a 12 foot pound rifle.  First string was longer (lots of shots climbing up to normal speed) and it looked like 2400-2450psi would have been the upper sweet spot limit.  So I shot the below string with a starting pressure of 2450psi.




Looks like my 2450psi start was a little high.

So with that rifle at that setting, will normally fill to 2350psi and just refill after 50 shots (this is one of the AA tubes with a quick fill and no gauge).  No big deal, will set 50 pellets aside at the beginning and just refill the gun when those 50 pellets run out.

[cactusrat]

Easiest way is to fill the gun, start shooting over chrony recording each shot. Number of shots depends on what gun you are shooting. Stop when the fps is well below the starting (first) fps.

Now take these numbers and add them to a spread sheet. Make a graph with these numbers. Now you have a picture of your shot curve.

Lets say shot #9 is where the string started leveling out and shot #25 is the shot that was at or a little below shot #9.

That’s you peak curve. Fill the gun back up and shoot it 9 times. Take a reading of the pressure left in the gun. Shoot until shot 25 and take a pressure reading.

The next time you fill the gun, fill only until what the pressure was at shot #9. Your first will then be in the peak of the shot curve. Shoot until shot #25 before refilling the gun (again to the pressure of shot #9).

Sound like a lot of trouble, but it’s not. Best part is there is no math, well just counting.

[Ribbonstone]

Some raw data.  Just wondering how others would divide this.

.177 Pneuma being tuned for 12 foot pounds (using 8.4gr. pellets in this string). Not real efficient (yet) but am working on that.

60 shots  with pressures occasionally added in (circled) along the way.





I’ll admit, that for goofing around the 20-30yard back yard, all 60 shots will work for hammering plinking targets, paintballs, etc.

But what spot would you decide (at this current adjustments) would be “sweet”.

[cactusrat]

The whole enchilada looks sweet to me. If you must have a curve, throw out the first eight shots and the last eight shots, then you would have a double dipped in chocolate sweet shooter.

[Ribbonstone]

As a pump filler, realized that filling all the way up and shooting 60 "pretty good" shots,  is pretty much the same as TWICE as much effort as filling to 160 and shooting to 130bar TWICE.

So as i have the control, would rather fill twice and get 60 shots inside of 15fps than fill once and get 60 shots inside of 40fps.

Until I get the final setting worked out, will be filling this one to 165 BAR and refilling at 125. That's only about 30-33 shots, but it makes me feel better to know that any miss is due to ME rather than some change in velocity.