Tuning Gamo Urban pellet probe o-ring

[DeadSilent]

Hi all, new here!
My Gamo urban's bolt/pellet probe is pretty badly chewed up maybe due to magazine issues?
I bought a viton o-ring kit from Harbor Freight upon reading another forum that they had used and I intend to attempt to replace it today.

Anyone else have this issue?

I cannot seem to find any specs on the o ring online which is hard to believe considering the Urban is a very popular starter PCP.
Thanks all, glad to be here!

 

[jarmstrong]

metric o-ring 1.5 cross section x 3mm ID
the steel face on the magazines have a punched hole that need to rounded out, the edges are rough and tear the o-rings quickly
I used the cone shaped Dremal bits then the rubberized cone shape bits for a final finish
remove the face plate to get to the inside edge of the hole, it is just a little tricky putting back together, but if I can do, you can also
a #36 o-ring from the hardware store will be darn close 3/16 ID x 5/16 OD

 

[DeadSilent]

metric o-ring 1.5 cross section x 3mm ID
the steel face on the magazines have a punched hole that need to rounded out, the edges are rough and tear the o-rings quickly
I used the cone shaped Dremal bits then the rubberized cone shape bits for a final finish
remove the face plate to get to the inside edge of the hole, it is just a little tricky putting back together, but if I can do, you can also
a #36 o-ring from the hardware store will be darn close 3/16 ID x 5/16 OD

You're the man.
I ended up finding a different o ring kit I had bought a while back and it was a perfect fit.
I'm going to add a picture for anyone who needs it for future reference.
-Top o-ring was the hardware store o-ring which I was going to replace with.
-Bottom left is obviously my old chewed up o-ring
-Bottom right is the exact fit O-ring - thanks to your help.

Also something I have noticed that upon the o-rings contact with the breech whilst pushing the bolt forward-
there is more friction if I have the bolt handle at a more upwards angle than a downwards angle.

Time to work on the mags if I get around to it today. Thanks again.