Squeezing more out of my Umarex Fuel

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:

Old breech seal
Old breech seal

Let’s take a look at the new one:

New breech seal
New breech seal

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:

Seal protrusion
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.

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Author: admin

I've enjoyed shooting and hunting with airguns since my early teen years. For over ten years, I have shared my passion for airguns on this website.

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