Abstract: A hydraulic breech mechanism uses a sealed reservoir of fluid to rigidly support the bolt 6 against barrel 2 resisting pressure generated by discharging a cartridge in chamber 3. Recoil forces cause the high pressure cylinder 7 and barrel assembly 2 and 4 to move relative to the sleeve valve 8 opening communication between reservoirs 9 and 11. This and subsequent bolt travel displace floating piston 12 compressing spring 13. During bolt opening any cartridge in chamber 3 will be ejected. With the firing load removed from the bolt 6 the floating piston 12 under influence of spring 13 will pump fluid into the high pressure reservoir 9, closing the bolt and chambering any round in the loading port. Continued load from spring 13 now returns the high pressure cylinder 7 and barrel assembly 2 and 4 to the original position relative to the sleeve valve locking bolt 6 ready for the next cycle.

Abstract: By providing an annular chamber 7 and a vent 11 to the radial gap between bolt 10 and high pressure cylinder 3, located between a seal 8 and a body of fluid 13 the operating range of the seal 8 cannot be exceeded. The flow rate of fluid from reservoir 13 into annular chamber 7 is restricted by the radial gap between bolt 10 and high pressure cylinder 3. The cross sectional area of both annular chamber 7 and vent 11 are greater than that of the radial gap between bolt 10 and high pressure cylinder 3 therefore fluid cannot enter annular chamber 7 at sufficient rate to cause a pressure rise in annular chamber 7 thus seal 8 is isolated from fluid at pressures above its safe operating range. Similar protection may be applied to any seal in the mechanism.

Abstract: A hydraulic breech mechanism uses a sealed reservoir of fluid to rigidly support the bolt 6 against barrel 2 resisting pressure generated by discharging a cartridge in chamber 3. Recoil forces cause the high pressure cylinder 7 and barrel assembly 2 and 4 to move relative to the sleeve valve 8 opening communication between reservoirs 9 and 11. This and subsequent bolt travel displace floating piston 12 compressing spring 13. During bolt opening any cartridge in chamber 3 will be ejected. With the firing load removed from the bolt 6 the floating piston 12 under influence of spring 13 will pump fluid into the high pressure reservoir 9, closing the bolt and chambering any round in the loading port. Continued load from spring 13 now returns the high pressure cylinder 7 and barrel assembly 2 and 4 to the original position relative to the sleeve valve locking bolt 6 ready for the next cycle.