What is a 3-gun?
Usually called 2-Gun or 3-Gun depending on the type of the replicas. It’s a kind of shoot competition in which each steps needs a competitor with a rifle, a fun, a pump-action gun or other types of replicas.
Multi-Gun has a lot of common things with the IPSC/USPSA: a shooting path in which the shooter has to pass different steps and attack the objectives with various different positions.
IPSC (International Practical Shooting Confederation) is a modality of the target shooting.