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Old November 22, 2012, 12:21 AM   #40
James K
Join Date: March 17, 1999
Posts: 24,160
That failure to fire sounds like too light a trigger pull, usually the result of tampering with the trigger or hammer, or too light a mainspring or trigger return spring.

What might happen is that when the trigger is pulled, the force required to release the hammer is so light that the finger does not keep the trigger back. That allows the trigger to move forward, letting the rebound slide and/or hammer block keep the hammer from falling all the way. The result is a misfire.

A comment on S&W hammer blocks. First, I don't know what a "1947" hammer block is. S&W has used three different types of hammer block safety. The last and current type was first used in December 1944 on the M&P "victory model", the only revolver in production at the time, and was installed on all post-war production. S&W has never used a transfer bar.

Originally, S&W thought the old style rebound hammer would act as a hammer block, but it was not strong enough to keep the gun from firing if dropped hard on the hammer. They then thought the rebound slide would be good enough, but finally had to install a hammer block to compete with Colt's "positive" block. But S&W's first two blocks were not positive, being spring loaded into the blocking position. Finally, Carl Hellstrom, in 1944, designed the block that is used today and is positive.

Tests have shown that under extreme blows, the rebound slilde can be crushed or the hammer stud sheared off, allowing the firing pin to reach the primer of a cartridge if there is no hammer block. Would a transfer bar do the same thing? Yes, but transfer bars have the disadvantage that they are struck a blow every time the gun fires or is dry fired and have been known to break under that stress. A hammer block is not stressed, since it is never touched by the hammer unless it is needed, after other safety systems have failed; it is the last protection, not the first.

Jim K
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