All British Sovereign and Half-Sovereign coins produced from 1817 to present are 22 carat gold.
The "BF" is more likely a "BP". It is not a mintmark, it is the initials of the designer of the most commonly used "St. George and the Dragon" design, Benedetto Pistrucci. The Pistrucci design appears most commonly on the British Five Pound, Two Pound, Sovereign and Half-Sovereign gold coins since 1818. It has also appeared regularly on predecimal Crown (Five Shilling) coins since 1818.
British 1913 Halfcrown coins were minted in 92.55% silver only
A coin of 1913 cant be of Queen Victoria as she died in 1901, the veiled head was used from 1893 to her death in 1901. A coin showing St George and the dragon is 5 Shillings (A Crown) if Silver, and is either a sovereign or half sovereign (20 or 10 Shillings) if gold. The BM mark is the designer of the Monarchs head on British coins, But was only used from 1911 onwards on the coins of George V. BM stands for Bertram MacKennal. This Coin cannot be a legal tender issue, but could be some type of gaming token, as stated, Queen Victoria had died 9 years before BM showed on coins, but would be inline with a coin of 1913 but depicting king George V. A Crown of 1913 was not issued that year, so would be one of the smaller gold coins.
The Sovereign Soul - 1913 was released on: USA: 18 March 1913
There were no British Crown (Five Shilling) coins issued from 1903 to 1926.
Benedetto Pistrucci (BP), designed the original St George and the Dragon design in 1817.
Whatever British coins were being minted in 1916, were still being minted in 1918. The Half-Sovereign coin was not minted in 1917, but resumed minting in 1918. The Half-Sovereign was only periodically minted during the 20th century predecimal period, and was not minted at all from 1927 to 1936 and 1938 to 1979 inclusive. The British Third-Farthing coin ceased to be minted in 1913, although it was only minted specifically for Malta.
All Sovereigns were worth 1 Sovereign (1 Pound or 20 Shillings) when new prior to Britain coming off the "gold standard". After the "gold standard" the Sovereign was worth whatever its weight in gold represented.
What George Did - 1913 was released on: USA: 17 January 1913 UK: 6 April 1913
Who Killed George Lambert - 1913 was released on: USA: 8 September 1913
"georgivs v d g Britt omn rex f d ind imp" does not identify the coin, in very abbreviated Latin, it identifies the Monarch. All British Commonwealth countries have variations of this expression on their coins. "GEORGIVS V D G BRITT OMN REX F D IND IMP". The literal definition is - "George V by the Grace of God, King of all the British territories, Defender of the Faith, Emperor of India". If the coin has no country name on it, it is probably British. If it is gold and has a mounted St George slaying a dragon on the reverse, it will be either a Sovereign or a Half-Sovereign. Sovereigns and Half-Sovereigns are identical except for size. There should be a tiny little letter underneath the horses rear foot indicating where it was minted. None for London, C for Ottawa, M for Melbourne, P for Perth, S for Sydney. There is some value to these coins.
George Barnwell the London Apprentice - 1913 was released on: UK: February 1913 USA: 31 July 1913