A hammerless pigeon gun by Purdey will generally weigh around 7lb 8oz - 8lb in 12-bore. Some have straight-hand stocks and splinter forends but many made for the USA between the 1920s and 1950s have pistol-grips and beaver tail forends.
The pigeon gun will have a bigger, stronger action with deeper fences (often with sideclips)and bigger lumps and bolts. Actions are sometimes bolstered at the radius. some pigeon guns have no ejectors and non-automatic safeties or no safety at all are common options,.
The stocks will be set-up to shoot high, like a trap gun. The barrels will often have 'LC' or 2 3/4" chambers intended to shoot 1 1/4oz of shot. the rib will generally be a raised, matted one with a flat surface. It will have heavier barrels than a game gun.
The game gun will typically weigh 6lb 2oz to 6lb 12 oz, straight-hand stocks, lighter barrels, chambered for 2 1/2" shells and often regulated for 1 oz , 1 1/6 oz (or 1 1/8 oz in earlier guns).
The stock will be straight-hand, splinter forend, balance just forward of the hinge pin and set up to shoot to point of a impact with 60% of pattern above the mark, 40% below.
Pigeon guns absorb recoil well, are steady and suited to shooting repeatedly at a going-away targets from a fixed point with repeatable dependability. Game guns move faster, change direction quicker and are generally more 'lively'.
Typicall y pigeon guns are choked tight and a game gau will be more open - I.C / I.C or I.C / 1/2 Choke are common game chokings and Full/Full is common in pigeon guns.
