Thanks Mike. I reduced my regulator setting a tiny amount today and seem to have fixed my "first shot lower velocity" issue. With a max'd out hammer spring. I need to shoot this some and confirm I really did fix the first shot. Velocity increased about 10 fps. I might be happy with where the gun is but, if not, a small reduction in the poppet diameter seems worth a try. I do not have a lathe but do have a drill press and fine sandpaper. And a dremel but I do not envision using that. I looked at a bunch of your posts on GTA tonight. I will probably go through Jason's tomorrow. Thanks for generously sharing your knowledge.
Jim, I've enjoyed following your journey with the platform. I wrote a lot about the p15 over a few years, but keep mind it was a LOT of trial and error.....so i would recommend giving the later posts more weight than early posts. Really I didn't begin to fully understand the platform (and PCP function in general) until I converted it from
22 to .25 using an Mrod barrel. The early .22 posts were mostly learning what NOT to do, lol.
I recommend careful study of the relationships between poppet travel, valve seat/carrier and hammer travel before making any changes. It is easiest to do this with these pieces removed from the gun.
This is a very tight space and tiny changes can affect other aspects of neighboring function/operation
For example...
Reducing poppet od will result in the poppet sitting deeper in the funnel-shaped valve seat. In turn this will cause more stem protrusion....in turn this reduces hammer travel, reducing hammer strike capability in an already marginal syste.
Measure stem protrusion, at minimum do not exceed the OEM measurement. Also recognize that any protrusion greater than half the throat ID may be considered as surplus, and candidate for reduction/shortening. This will actually increase hammer strike capability due to increasing hammer travel.
There is a very fine line here where you can significantly increase hammer strike by increasing hammer travel. Hammer travel can be maximized by both reducing stem protrusion as well as one can machine of a mm or so of the hammer face, shortening its length, increasing travel in the process. In this application the increase in travel far outweighs the slight reduction in hammer mass...too much stem protrusion= too short of hammer travel...too little stem protrusion and the hammer will bounce off the valve, reducing dwell and of course velocity. Optimization of this area can yield performance previously unattainable.
With this platform in particular, as one is working towards a goal of >45fpe with good efficiency at lower reg settings/higher shot count, step 1 should be to get the porting to 75- 80% of caliber. After that is achieved, fine adjustments around the valve and hammer system like I described above will make achieving the goal much easier. A 2mm stemmed, minimum diameter peek poppet will make exceeding 60fpe at 140bar or less a relatively easy task........45fpe will come at less than 130 bar, likely as low as 110-115bar.
It is a very capable platform, my learnings here made it relatively straight forward to achieve my desired goals when shifting over to the Gen 1 Taipan Veteran. Other than the differences in quality/precision/robustness, the Veteran has slightly more hammer strike capability than the p15, with a couple more mm of available hammer travel, a couple more grams of hammer mass, and a much more powerful hammer spring system. In comparison, my veteran Long is a >60fpe .22 slug shooter at 135bar, or a >85fpe .25 slug shooter at 145bar depending on which barrel I am using. The key change in the Veteran was increasing throat area to 85%or so of bore area by reducing stem diameter.....IMO this is the missing link for many who experienced hitting a "wall" in their journey towards higher energy slug shooting with their OG Veteran.
I hope you proceed in optimizing the valve and hammer system, this will make your .25 P35 really perform. Some of this may apply to the smaller calibers as well, but I have no relative experience to share. .177 and .22 slugs likely require a slightly different recipe.