I received my Pro 800 few days ago, and I am getting to know the new machine. Coming from a Breville Dual Boiler.

I am trying to run it as a volumetric machine since it looks like I can actually pull a perfect 23-25 gr espresso lungo (with no residual water going into the drip tray).
Taking the idea from another discussion, I reduced the flow rate by setting the screw that regulates the flow from the boiler at 3/4 of a turn from the zero. Boiler temperature is set at 242F. I pull the lever and I raise it immediately. The preinfusion is kept to the minimum if any, and I can get exactly 23-25 gr each time. I am including two videos with the last two shots I made.
I am using 7.5 gr of coffee, single dosing with a Niche Zero, Buongiorno Primavera. The result is consistently excellent. I really like it, I would say 90% satisfied just because I know improvement are always possible. The temperature of the group seems to be reasonably stable as well, even after few shots in sequence. Maybe that is due to the lesser amount ow water that flows trough it. The pressure in the boiler seems to be at about 0.8 bars, and I can still get enough steam for the milk. As I mentioned I am also not getting any residual water in the drip tray, and that is an additional big benefit.

I have a few of questions, since I am planning on using the machine mostly in this way if it shows to be as consistent as I have seen it so far.

First, I assume there are no problems in operating the level in this way. The machine seems to be very solid. However I thought it was better to ask if that can bring any premature wear to any of the components.

Second, judging by taste, I don't feel that the coffee is under extracted. However I also think that since I am not filling the chamber completely, the springs begin to compress the water when the piston has already reached a lower position if compared to when the chamber is instead completely full. I assume that in this way the initial pressure is not the full 12 bars. Again, I am satisfied with the initial results but I am planning on checking the pressure at the portafilter as soon as I receive a new gauge (the one I have is broken). Has anybody tested the pressure in this conditions. Probably not but ...

Finally, not that I am planning on doing it right now, but does anybody know if the two springs can be replaced with different ones of different strength?

Any other comment or advice is welcome.

In both videos I did not start the timer promptly at the first drop, however it still gives an idea of the flow rate.

I have a different machine with the same group.

That is an interesting way to use it. I have not tried that before but I think I will.

If you carefully look at the lever position where the water starts/stops flowing and the position where it reaches full flow you may be able to accomplish the same thing with less lever travel. You can also fine-tune the time the water is flowing to control the volume. By adjusting the speed of the water flow rate using the screw you could determine the duration of the lever movement you need.

That will probably be a low pressure shot.At what clocktime does the lever engage?
Do what tastes good to you.

Yes. As I mentioned I expected the pressure to be lower. The position of the lever is definitely an indication, thank you for pointing it out. The other one is that if I do a six seconds preinfusion (allowing the full amount ow water in the chamber) in order to get a similar flow rate I have to turn the Niche Zero two notches down. That is why I mentioned the possibility to change springs with stronger ones. Again, not that I am going to do it now. I have received new coffee and I will see what happens with a different blend. I like the result with Primavera, but maybe it's just that coffee.

Here is a picture that shows the position of the lever at : (blue) when the lever engages after 6 seconds preinfusion, (green) when it engages with no preinfusion; and (red) rest position. Still with the valve at 3/4 of a turn from zero.
Difficult for me to translate it in actual pressure. There is a chart that I found in a discussion that shows the infusion pressure for the Profitec 800, but it's a function of time not position of the lever. However based on that diagram I would say that if the pressure at "full forceI" is really only 9 bars as shown in that chart (I thought it was 12bars), running the machine in this way the pressure is not higher than 8, maybe 7 bars. If instead in normal condition it starts at 12 bar, maybe in this case the pressure is not higher than 9 or 10 bars. I'll check the time it takes to get from "blue" to "green" and then to "red", in order to see if I can come with a more reliable number number, still based on that diagram.

I tried this method with two more blends.
The first one was Belton's Bonsai Blend. I did not get the same good results as with Primavera. Good enough espresso but not at the level of when I make a normal pull with "full" preinfusion. The chocolate aftertaste that I like so much with this blend was not showing up. Again, good espresso, but it was like a different blend. Goin instead on the complete opposite direction, prenfusion until the first drop and then 30 seconds extraction, gives me the best espresso I can wish for.
The second one, still playing with it, is Buongiorno Banco Gotiti. Terrible results, for my taste, too much acidity, while my wife prefers it like that. She drinks it as a cappuccino.
So far I would say 1.5 out of 3 .