Tuning STUCK halfway thru' Seneca Aspen/Nova Freedom Pump Repair - PHOTOS

That's exactly what it is for. What it does is you don't have to pump as many times to get to a pressure where you can still shoot the rifle. The best way to keep your pump working a long time is to pump slowly up to the pressure you find is the sweet spot then after each shot give it 5-6 pumps to maintain that pressure before shooting it again. Your pump will love it and your accuracy will benefit. You are the regulator.
 
So it is more beneficial to fill the precharge section back up to 1800 PSI? Is there any advantage to leaving the front section of the air tube "discharged", like maybe more air capacity? I just invested in a compr3ssor to do most of the filling and as you mentioned just just the hand pump to top up between shots.

I curious what fps yoj are normally shooting at with the 2800-3000psi you maintain? Also do you normally leave the gun power valve on Low or High for most shots? I'm finding High gets me in the 900fps region and the low setting more 750fps. I prefer the 900fps range and impact with the .25 cal.
 
I use to keep mine around 3000 psi. As far as the poppet you might be able to get someone to make you one out of delron. I have a peek poppet in my liberty which uses the same valve as the Aspen that Duy made for me but I don't think Duy is still making them anymore. I can't remember what kind of fps I use to get at 3k as mine started leaking from the check valves about 3 years ago and it's sitting in my airgun shed in pieces.
 
Hoping someone can help me resolve/identify an issue i have recently with my seneca aspen. I recently replaced all orings in my aspen (valves, piston, seals etc) and upon a pump test all was working perfectly (no 1700psi precharge in air tube). I also got a special fill probe sent out to me thanks to soupyyy. After precharging the front of the air tube to 1700psi, as per the assembly manual I tried 60 hand pumps to see if it would reach the recommended 3000psi (+/-300). I did this in 10 pump intervals. What I was noticing was a strange "twang" sound on each pump stroke as the pressure built up, and the pump became harder to pump and almost impossible to fully extend on the outward stroke.

I released all air (front precharg too), took the pump apart and found both 2.5 x 7.5 orings on the check valve were deformed. I also found that the "shoulders" of the copper valve were broken off inside the receiver (see image below)
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My questions are:
Could this be what was causing the "twang" sound And resistance to the pump?
Can I still use the valve without the "sholders"?
If not how can I fix, or replace it?

Any help or advice would be much appreciated🙏

PS gun works fine if filled by external pump and shoots fine. Just a real pain to keep hooking it to a pump after every 2-3 shots to keep in in the sweet spot.