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Old June 12, 2010, 10:37 AM   #1
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hammer block

I would like one of you folks to tell me why the hammer block on S&W revolvers is necessary. I am unable to see how the trigger rebound spring housing would allow the hammer all the way forward without the trigger being pulled. Anyone?
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Old June 12, 2010, 12:26 PM   #2
Jim Watson
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The rebound slide can be bounced out of engagement by inertia if the gun is dropped. The key incident was in 1944 when a .38 M&P Victory Model went off when dropped on the deck of a ship and killed a sailor. S&W redesigned the hammer block - they had hammer blocks since as early as 1905 or even 1902, but not absolutely positive in action - to prevent accidental discharge.

Colt's hammer block, introduced in the 1905-1908 time frame, was always positive in action, the reason for naming guns with it "Pocket Positive" and "Police Positive." They didn't rename the New Service or New Army, though.
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Old June 12, 2010, 12:58 PM   #3
4V50 Gary
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If you examine the rebound slide, there's a small, flat step on the top of it. When the trigger isn't pressed and the hammer goes forward, the rebound slide's spring pushes the rebound slide forward much faster than the hammer can rotate forward. The rebound slide's step blocks the hammer from rotating fulling forward such that it's firing pin doesn't strike the cartridge's primer. It does this by intercepting the hammer seat (the flat surface) on the bottom of the hammer.

This feature is why I've always argued that the S&W revolver is superior internally to the Taurus. Early Taurus revolvers had this design, but eliminated it to simplify production (and costs).
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Old June 12, 2010, 03:15 PM   #4
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I knew you guys would know..Thank you.
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Old June 12, 2010, 09:37 PM   #5
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Also, due to wear or just impact, the engagement surfaces of the hammer and rebound CAN simply break or be forced, allowing the hammer to move forward.

The hammer block is a "belt and suspenders" addition to insure that no amount of force can fire it.
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Old June 12, 2010, 09:47 PM   #6
James K
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Well, not quite. If the hammer is struck hard enough, it can crush the rebound slide and/or shear the hammer pin, allowing the hammer to go forward and fire a round. The hammer block prevents the firing pin/hammer nose from reaching the primer no matter how hard the hammer is struck.

FWIW, the purpose of the rebound slide is not to act as a hammer block. It is necessary in a side swing revolver to retract the firing pin from the fired primer to allow the cylinder to open. In the S&W system, that means the hammer has to be retracted.

In the old top breaks, a rebounding hammer was not as necessary, since the opening cylinder was moving the cartridge away from the hammer.

Just to avoid some confusion, S&W did not change their hammer block system when they went to frame mounted firing pins, and the hammer block is NOT a transfer bar.

Both Taurus and Ruger use transfer bars, another way to solve the problem of a blow on the hammer. With that system, the hammer cannot reach the frame mounted firing pin until the trigger moves the transfer bar between them. The firing pin has a retracting spring, solving the problem of swinging out the cylinder without a having a rebounding hammer. I don't think either system is superior; the rebound slide is the more expensive.

Jim K
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