Jon,
I'm surprised to read that you have 30mm mortises in 75 mm timbers. We generally keep our mortises to 1/3-1/4 the width of the timber, and wouldn't make a mortise in a 75mm timber any wider than 20-25mm. Mortises do more damage than any advantage a thicker tenon provides. Maybe that thicker tenon and thin mortise walls is a cause of the blow-out you mention. In my opinion you should try to always have mortise walls on both sides of the tenon (and pin penetration on both sides) equal or more than tenon thickness.
By the way, I learned the 1/3 maximum rule of thumb from compagnons in France.
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Will
www.heartwoodschool.com