Military tacticians and historians often make use of the term 'tip of the spear.' It refers to a combat force that is used to puncture the enemy's initial lines of defense, to be quickly followed by concentrated forces which destroy any remaining threat.
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bolt action, type of breech mechanism that was the key to the development of the truly effective repeating rifle. The mechanism combines the firing pin, a spring, and an extractor, all housed in a locking breechblock. The spring-loaded firing pin slides back and forth inside the bolt, which itself is the breechblock.