You need to replace the stock/Buna oring with a Viton 75d. Issue solved.
I ordered viton orings when I ordered the buna, so I have both and will try Viton next..
Thanks.
You're welcome. I replaced mine a couple weeks ago. After removing the seal, I gave the barrel a good cleaning and seated the new one with a dab of high temp vacuum seal grease. Should be good to go for lots of shots.
Replaced the buna with Viton last night. Headed to the range this A.M. and fired almost one tin of JSB Monster Jumbo (redesigned) pellets with no disheartening issues noted.
Of interest is that groups tightened up at 25 yards. Groups with the original buna orings were 1"CTC or more (at an average 903 FPS). Today sample groups (same distance and average FPS but with worse winds) included .394", .330", .338", .439", and .530" CTC. Note that even tighter groups may have been possible by those with steadier hands than mine.
Pictures of the groups are available if anyone really, really needs to see them.
I then put a 1/10th size steel Silhouette chicken (roughly 2.5" X 2.5") at 77 meters and took aim. In gusting winds I was able to make clean hits 5 out of 10 times with out too much trouble. A better result would have been possible by anyone who would have taken the time and effort needed to better read the varying wind gusts.
Next, I need to get paper targets out at 77 meters and 100 meters and see what happens. I also need to reprogram the RW HP to increase pellet speed another 30 to 50 FPS.
Fortunately, I was able to pick up a programming device this morning when I stopped in at AoA. Unfortunately, I need to read the directions and watch the Youtube videos so I can figure out how to operate the device.
Fortunately, I used to run a software development and sales company that put out a product I designed. Unfortunately, I no longer have software engineers much, much smarter and much more skilled than me available to operate the programmer.
Fortunately, device operation looks straight forward. Unfortunately, my level of patience is indirectly proportional to my age.....and its getting worse.
Enough said on programming.
Finally, I believe that today's shooting results were as good, if not better, than those I would have gotten with the $2000 dollar .25 caliber bench rest rifle I sold recently.
Best wishes to all.
The other Mark B.