Your character size alters the damage dice or damage of all weapons you use.
Gnomes and Halflings (Small) therefore roll different damage dice both in melee and ranged.
The Enlarge Person spell will transform a Medium character to Large or a Small character to Medium.
The Weapons table on this wiki shows the more common Medium damage.
|Small character damage||Medium character damage||Large character damage||Huge|
|1d6 : when 2d4 reduced*||2d4||2d6||3d6|
|1d10 : when 2d6 reduced*||2d6||3d6||4d6|
* The Small column can be confusing as it shows 1d6 and 1d10 twice, so here is an example :
a Small character (Small weapon) doing 1d6 is Enlarged to 1d8, but a 2d4 Medium is reduced to 1d6. ( It could have been a simpler system.)