Thank you very much for such detailed replies. I think the problem may have been such low powered loads used at the start that obturation failed and by the 16th shot leading had or was occurring. Secondly I have inconsistent cylinder throats ranging from .357 to .35575.
My friend and gunsmith has read all your comments and has decided to ream all throats to .357 and use .357 projectiles with 2.7 Vihtavouri 310 about the same or slightly faster than 2.8 Bullseye. All this into a .3545 barrel with a nice throat. I am also using various HBWC with a range of hardness.
Going to the range for some serious testing Thursday and Friday. Lets hope the weather holds. Well, after all, it is England