General PCP tune question

[Franklink]

I think I understand some of the variables in a PCP tune (striker length vs spring strength vs port size vs fill pressure). I can only get about 30 good shots before velocity drops rapidly.  From 200 bar to 150 bar, or from 148 bar to 100 bar after I reduced the hammer length, it still will only give me those 30 good shots.  It has about a 200cc air tube (I think).  The 200 bar to 150 bar was about 30 shots right under 20 fpe.  The 148 bar to 100 bar is 30 shots right under 17 fpe. 

The 30, 17fpe shots from 148 bar to 100 bar is about the fpe I'm looking for.  I don't want to go down much less in power than that.  I assumed going from 20 fpe to 17 fpe would give me more shots but I drop off that plateau very fast at shot #31.  With the current tune I also can't fill it any higher than 148 bar or my starting fps is too low. So, I'm hedged in at that usable pressure.

The gun is very accurate for those 30 shots with consistent fps.

How can I get a longer shot string?

I'd like to get more shots for how big of an air tube it has (I'm used to playing with a Disco and a Hipac'ed 2400 so I expected more shots out of a larger tube). 

I think this is a general PCP tuning question but if it helps with an answer, it is a .177 Brocock Concept Elite that likes 10.5CPH.  I've also tried 7.9 gr and 8.64 gr pellets with a few less good shots per fill and decreased accuracy over the heavier pellets.

[nervoustrigger]

Running your numbers, the efficiency calculates out to about 0.88 fpe/ci so yes it should be possible to improve your shot count by at least 50%.  Every gun responds differently and unfortunately I'm not familiar with the internals of the Brocock Concept Elite but I would suggest looking into a SSG or a TSS to prevent air-wasting hammer bounce. 

Another approach is to use a bstaley O-ring buffer.  In my experience, the process of tuning requires more trial and error than a SSG or TSS but for most folks it will be easier to get started because all you need are some O-rings that are a snug fit to the inside diameter of the air tube and perhaps some washers or shims to fine tune the stack.  A few I've tuned have responded really well to this mod, yielding in the vicinity of twice as many shots as before.  It works particularly well when downtuning a bit.  Going from 20fpe to 17fpe isn't a significant downtune but I think you could get good results with some experimentation.