This is a spring loaded alternative to the buffers I have used for my other Gauge 1 models.
Salvage a spring from a ball-point pen and fit it to the buffer with a M2 screw.
You need to drill out the screwthreads in the bufferbeams to provide clearance for the screw when the buffer is compressed. I suggest to drill a hole ~1 mm larger than the diameter of the head of the M2 bolt.
Glue the assembled buffer to the buffer beam with CA glue.
The author marked this model as their own original creation.