Diana 5 Breech Seal

[Motorman]

I recently acquired a 1960-ish Diana Model 5. No breech seal. Bought one from Umarex and it came with a thin steel washer as well as the anticipated rubber O-ring. I presume the steel washer goes under the rubber O-ring? How can I tell if there's already one in there? What purpose does the steel washer serve?

Thanks for your help!

Motorman
St. Louis, MO

[Roadworthy]

I guess if you want to know if there's a steel washer under your breech seal you'll have to pull the existing breech seal.

The washer probably serves as a shim or spacer to raise the breech seal a bit higher.

[WD Feese]

The washer is a shim which you may not need.  If velocity is low then shim.  Might try a pick in the seal grove to an old shim.