Boresighter trainer for gun

A boresighter/trainer configured for use within a gun barrel of a gun, the gun barrel with a first end having a firing chamber and a second end, the boresighter/trainer comprising:

• (a) a body having an axis, a proximal end, a distal end configured to be inserted into the second end of the gun barrel, and a seating portion between the proximal end and the distal end, the seating portion configured to form a first contact area with an inner surface of the gun barrel;
• (b) a bore adapter attached to the distal end, the bore adaptor having a variable adapter diameter and configured to form a second contact area with the inner surface of the gun barrel;
• (c) a fastener attaching the bore adapter to the distal end, the fastener configured to apply force to the bore adapter;
• (d) a light source in the housing to emit a light beam aligned with the body axis;
• (e) a power source,
• (f) a sound sensor to detect the sound of a firing pin strike of the gun, and to activate a circuit in response, wherein when the circuit is activated, the power source provides power to the light source and the light source emits light;
• and
• (g) a switch, wherein the switch has a first position in which the boresighter/trainer is in a first mode whereby it constantly emits light, and the switch has a second position in which the boresighter/trainer is in a second mode whereby it emits light for a short duration when the sensor detects the sound of the firing pin strike, wherein when in the first mode, the boresighter/trainer permits laser light to be projected along a longitudinal axis of the gun barrel in which it is portioned, for aligning a sight on gun and wherein when the boresighter/trainer is in the second mode and the firing pin activated, the sound of the firing pin is detected by the sound sensor and activates the circuit in the boresighter/trainer to cause the light source to emit light along the longitudinal axis of the gun barrel.