When was the last time you checked your breech seal? Breech seals get worn out over time and sometimes don’t even come installed in an optimal fashion. If you shoot a spring piston airgun, you will find this information to be very useful.
My Umarex Fuel seemed to shoot rather slow for a new airgun, 900 fps with regular pellets (7.9 gr.) and 750 with heavy pellets (10.5 gr.). Not much better than ten year old Gamo Shadow. I could just barely feel any protrusion of the breech seal, so I decided to try a new seal.
I found a replacement o-ring (14mm OD x 9mm ID) at a hardware store. Here’s the thickness of the old o-ring:
Let’s take a look at the new one:
The new seal is .18mm thicker, enough to feel a difference when it is installed. I decided to chronograph my airgun to see if this made any difference. Regular pellets now shoot 925 fps, and the heavies shoot at 800 fps. Not a bad increase.
I’m convinced that this airgun can do even better. I took my caliper and measured the seal protrusion:
Only 5 thousandths of an inch, it should be at least 15 thousandths for optimum power. The next step will be to construct a shim to bring this up a bit more. That will have to wait for another time, but I’ll take you all along when I get the time to tackle this project.