Ah HA!! PLUS ONE to PETTIFOGGER .... almost.
Agree, the Whisper Springs from "The Smith Shop" are very nice indeed. They work very very well. SlixSprings are also Very nice indeed. They work very very well. They are a little heavier than Whisper. When running the rifle "on the clock" you won't notice the difference. Both Whisper and Slix are intended for use in a Toggle Rifle with an action job and Positive Slam Down. In a stock rifle, with straight wall cases (44, 45, 38) you may find the fouling of the carrier block will cause the carrier to "stick" and stop the rifle. Positive Slam Down will eliminate this stoppage. If your rifle is bottleneck, 32-20, 38-40 or 44-40, never mind. The bottleneck cases run clean enough there is no issue.
May the Fourth be With You
Coffinmaker
PS: Short Stroke kits have Positive Slam Down built in.