I found this photo on the IWM Site. 18 Pound Artillery had an effective range of three miles and a well trained crew could fire thirty rounds per minute. Guns at Carnoy Valley were within range of Guillemont and no other assaults were taking place in the area on 30th July. Therefore, it is likely these men were assisting 90th Brigade in their attack on Guillemont.
The photograph shows men in the heat of the day and it is assumed this would have been around midday, or later. As such, the support to the infantry had to be necessarily limited to the Western side of Guillemont village. The 2nd Royal Scots Fusiliers had advanced to the centre of Guillemont, alongside the 18th Manchesters. Communication with Brigade HQ in Trones Wood and 16th / 17th Manchesters to the east of the village had been broken by the German bombardment and machine guns – limiting the prospects of British bombardment without hitting their own troops. For more details see Guillemont | 17th Manchester Regiment on the Somme