Plea for information about grandfather's medal

Sir--My grandfather, Mr David Kirbyson, was awarded the Military Medal in 1916. 38191.

Pte Kirbyson D. Served in the RAMC. After WW1 he lived in Mexborough at 70 Victoria road The London Gazette dated 21.12.16 stated that the award was given "for bravery in the field" but no specific action was mentioned.

I'm trying to find if there are any records or copy of the citation as to how he earned the medal.

Jack Wilson, High Bank, Chetwynd, Aston Newport, Shropshire.