Sevens, what is your load recipe for the 158gr bullets?
I've run a handful of different loads, but generally speaking, these have worked for me with 158gr bullets:
13.5 to 14.0 grains of 2400
8.3gr Hodgdon Longshot
16.0 to 18.0gr Hodgdon Lil'Gun
6.3 grains of Universal, a much lighter & middle of the road .357 Mag load would not run the Coonan.
I tend to run more 125 and 130 grain slugs lately, because I got a very good deal on them so I have a large supply on hand. I've also been playing a bit with cast lead 180gr slugs with fantastic results.