45 Colt with 19.9 and 20.7gr H110 under a 300gr XTP failed to ignite with WLP primers.
45 Colt with 20.6 to 22gr Ramshot Enforcer under 260gr SWC didn't ignite with Wolf LP primers.
357 Mag with 16.9 to 17.8gr Enforcer under 125gr SJHP did not ignite with Winchester SP primers.
Hmm, you said you had problems with w296....
I've tried 10% load reduction with W296 and had some that didn't light off with mag primers.
But of those you listed,
the 45 colt ramshot load may have been divine intervention since even 19.9gr would be over the maximum
recomended even for a ruger, the max listed by ramshot for a 225gr bullet is 23.5gr, so if you are stuffing 22gr under a 300gr bullet.....
the 357 mag load with enforcer is right in the ramshot recomended range, so I dont know what going down 10% would have to do with that one?
and the h110 45 colt load you list is below the starting load recomended by hodgdon... The rule is, start at the recomended starting load, but IF NONE IS LISTED go down 10% from max..... Going below the starting load is, in many cases, asking for trouble.