8fpe is plenty with proper placement but I think in practice you are likely to become frustrated with the number of fly-aways. A few key things at play here:
1. Accurate ranging (holdover/holdunder) is critical when starting at a very modest muzzle velocity of ~620fps. Very loopy trajectory.
2. CO2 is sensitive to temperature swings, making the holdover/holdunder subject to even greater error. I’ve read some of your posts so I know you’re well aware of that, so I will assume you’ve done everything within reason to mitigate its impact. But the reality is, it will always be there to a greater extent than if it were HPA.
3. This last one involves a bit of conjecture but the terminal velocity for your 35yd example is going to be somewhere in the vicinity of 500fps (14.3gr @ 500fps = 8fpe). At low velocity, a pellet is more easily deflected by thick layers of feathers or a bone…if only a little. Depends on the angles. The quarry’s elevation relative to you, the angle it presents to you (frontal, broadside, quartering), and the location of the POI. All of them will influence the extent to which the pellet’s path through the quarry is affected, and sometimes the difference between a clean kill and a flyaway is the 1/8” it missed the vitals. A faster moving pellet would be affected less.
I really don’t mean for this to come across negatively, I just hope it gives some perspective and presents some factors for further consideration.
For example, a while back I posted a scope cam clip here showing a squirrel at 30yds with a .177 wadcutter at ~4.6fpe terminal energy. It was an instant lights out but it was done in pretty much ideal conditions…known distance, good support, no wind, etc. Definitely not a good choice were any of those factors altered.
