was granted in 1931 and it probably came into production around 1933 (ref. J Walter). A UK patent was applied for but was rejected in 1932.
The strange thing about your pistol is that the "a" at the end of DRPa means patent pending, although from the above information one would conclude the pistol wasn't in production before the full patent was granted...
Maybe the "pending" refers to the UK patent application? Or perhaps John Walter is wrong and it was made before the full patent was granted? I don't know.
Anyway the pistol was apparently on sale for the rest of the 1930s, so that gives you a ballpark date.
Values are not very high since while beautifully made, it's a simple pistol that seems to have sold in quite large numbers. In the UK a dealer might expect to sell a DRP mod 5 in good condition for around UK£120 and a private seller for perhaps £70 or £80. As always with valuations of old airguns, "condition is king".
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