Abstract: One aspect of this gunite or refractories gun is a seal-clamping system that applies an essentially constant force despite variables such as wear of the seal or seals. Another aspect is a combination of hydraulic control and mechanical cams to clamp the seal(s). Ideally both aspects are used. Preferably the system also balances seal-clamping forces at different points. Chambers in a rotary feed structure carry material from a hopper at a receiving port to a delivery tube at a discharge port. Gas (usually air) flows from a pneumatic supply orifice to blow material from the feed structure into the distance port. One or more seals are used to seal the path that is formed by the pneumatic supply orifice, at least one chamber (when generally in position for discharge), the discharge port, and the delivery tube. A set of cams or other mechanical apparatus applies force to press the seal(s) against the feed structure.