It looks like "R Watt Jnr" [junior] to me.
Of course, it could have been furnished by the Brimingham trade to a jeweler or some other retailer that wasn't primarily a "gunmaker" and isn't listed anywhere as such. Since most "gunamkers" didn't actually make guns, the name often only represents who sold it. We tend to associate the B'ham trade with middle to lower quality guns but there were also makers who could rival the London trade if the market demanded it.
One of the real curiosities are B'ham made guns of London quality with fake London makers marks that were made new to be sold on the used gun market. This was because a used Manton or Mortimer would sell more readily than a new gun by an unknown maker regardless of how good he was.
By the 40s & 50s its likely that most London guns, or at least the locks and barrels, were really made in in Birmingham.