Reduced Power Buffer Spring. We collaborated with two prominent commercial ammunition manufacturers and two prominent gunsmiths to arrive at the design for the Yellow spring. It’s approximately 20% lighter than the White spring, and was the consensus choice out of 4 different evaluation samples provided to all parties. They all added in their final evaluations that if a particular gun needed a lighter spring, that the gas port should be enlarged for overall reliability. The Yellow spring is also appropriate for with low power SRTA training or SIMS Rounds for training operations. Color coded YELLOW.