If you have trouble with mast chips spitting out. Check your mast pivot bottom for sharp areas. If you feel any, clean them up with a file. Also you can cut 4 small darts in the teflon chip 90 degrees apart. This will help the chip form the cup shape.

Avoid very thick mast chips because it lifts the mast up so that the mast stops barely hit which I think causes them to wear quicker.

cheers
Bill J