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The ability of captive-bolt equipment to deliver an effective stun is mainly dependant on the velocity of the bolt. Lack of regular maintenance can significantly reduce bolt velocity and the efficiency of stunning.

Increased friction caused by a build-up of carbon deposits and/or defects in the firing chamber are the main conditions which lead to reduced bolt velocity. A build-up of carbon deposits in the breech of a stunner can reduce the velocity of the bolt by 50 percent. If the bolt cannot retract fully into the breech the explosive pressure exerted on the piston will be reduced, due to the increased size of the expansion chamber. This can also occur if any of the recuperator sleeves are worn. Similarly, if there is excessive wear on the piston, cylinder or flange, gases will escape around the piston and the propulsive force will be reduced. Corrosion, or build-up of carbon, can also cause increased friction around the cylinder, bolt and undercut.

The biggest single cause of power-loss is the failure of the bolt-piston to return fully into the breech after the shot, whether this is done manually or automatically. Where recuperator sleeves are fitted, care must be taken to ensure that when the muzzle is screwed into position it causes the sleeves to be compressed. If this does not occur, either insufficient washers and sleeves have been fitted, or some sleeves are worn and must be replaced.

Captive-bolt stunners should be dismantled, cleaned and lubricated after use even if they are used only a few times in the day, or even less frequently (see Step-by-Step Maintenance). Back-up equipment must also be regularly serviced, even if it has not been used. The continual use of the captive-bolt, as occurs on a busy line in a slaughterhouse, causes comparatively less build-up of carbon than sporadic use for the same number of shots.

In the EU, manufacturers of stunning equipment are required by law to provide instructions for the safe and proper use and maintenance of the equipment; manufacturers' instructions must always be followed.

Daily maintenance must include:

  1. Dismantling of the stunner.
  2. Visual examination for evidence of damage and signs of excessive wear.
  3. Removal of blood and water.
  4. Removal of carbon deposits from the breech and undercut.
  5. Checks on the condition of the recuperator sleeves.
  6. Reordering of the recuperator sleeves on the bolt assembly.
  7. General lubrication.

Daily removal and cleaning of the bolt assembly reduces the chance of excessive wear on any one part of it, ensuring continued, efficient operation.

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