From time to time, you will hear "The Experts" talk about the safety bridge. To a new M14/M1A owner, the safety bridge can be a bit of a mystery. Here is an explanation of what it is:
Just above the magazine latch, there is a groove in the area of metal just below the bolt that we call the "Safety Bridge". The M1 Garand and the M14 designs use a free-floating firing pin inside the bolt. If the firing pin channel is clogged or dirty, the firing pin may jam up, protruding from the face of the bolt.
If there is no safety bridge, then there lies a possibility that when the rifle chambers a new round, it can ignite the round before the bolt is fully locked. This will result in an "out of battery explosion" (not to be confused with a slam-fire). If the locking lugs of the bolt are not engaged into the locking recesses of the receiver, there will be nothing holding the bolt in place if there is an out of battery explosion.
The bolt will, in essence, act as a high speed battering ram and slam into the heel of the receiver. This can typically result in the catastrophic disassembly of the receiver, automatic magazine and trigger guard removal and shearing of the bolt roller and operating rod at one or more stress points. Considering the close proximity of the shooter's face to the heel of the receiver, it is highly recommended that you ensure that your safety bridge is functioning properly.
This is the safety bridge...
This photo has been deleted at the request of (former member with an apparent attitude) Tonyben
When the bolt is fully engaged into the bolt lug recesses, the firing pin will line up with the slot in the safety bridge allowing the firing pin to move forward and ignite the cartridge.
This photo has been deleted at the request of (former member with an apparent attitude) Tonyben
If the bolt is not fully engaged, the firing pin will be blocked by the safety bridge and prevent a premature detonation of the unchambered cartridge.
This photo has been deleted at the request of (former member with an apparent attitude) Tonyben
Over time, the tail of the firing pin may begin to deform and it may begin to advance sooner than a new firing pin.
If you have any questions, please feel free to ask here or post a question in the general forum and I am sure an expert will be along to help answer questions.
Edit: Here is a commentary sent to me via PM...
"When the M1a first came out, not Devine's as I recall, but the people after Elmer, many of the receivers, maybe all of them, had the firing pin cam cut in the wrong place. The pin would catch and fail to go fully into battery. At that time, it was common practice to round off the matching area on the Firing pin.
It was not unusual to see rifles where the cam area was gouged out from this misalignment. Other Brand receiver's had the same problem only worse.
It was suggested that a non chrome pin should be used thus transferring the wear to the pin only. I think this helped. I did see several rifles that fired on going into battery from worn cam areas. There was NO correction for this situation short of a new receiver.
There is a special gauge to check another situation, called Bridge advancement, this was during the M1 days. The bridge can and has advanced over years that produces slam fires. Ted Brown has the only gauge that I know about."
Just above the magazine latch, there is a groove in the area of metal just below the bolt that we call the "Safety Bridge". The M1 Garand and the M14 designs use a free-floating firing pin inside the bolt. If the firing pin channel is clogged or dirty, the firing pin may jam up, protruding from the face of the bolt.
If there is no safety bridge, then there lies a possibility that when the rifle chambers a new round, it can ignite the round before the bolt is fully locked. This will result in an "out of battery explosion" (not to be confused with a slam-fire). If the locking lugs of the bolt are not engaged into the locking recesses of the receiver, there will be nothing holding the bolt in place if there is an out of battery explosion.
The bolt will, in essence, act as a high speed battering ram and slam into the heel of the receiver. This can typically result in the catastrophic disassembly of the receiver, automatic magazine and trigger guard removal and shearing of the bolt roller and operating rod at one or more stress points. Considering the close proximity of the shooter's face to the heel of the receiver, it is highly recommended that you ensure that your safety bridge is functioning properly.
This is the safety bridge...
This photo has been deleted at the request of (former member with an apparent attitude) Tonyben
When the bolt is fully engaged into the bolt lug recesses, the firing pin will line up with the slot in the safety bridge allowing the firing pin to move forward and ignite the cartridge.
This photo has been deleted at the request of (former member with an apparent attitude) Tonyben
If the bolt is not fully engaged, the firing pin will be blocked by the safety bridge and prevent a premature detonation of the unchambered cartridge.
This photo has been deleted at the request of (former member with an apparent attitude) Tonyben
Over time, the tail of the firing pin may begin to deform and it may begin to advance sooner than a new firing pin.
If you have any questions, please feel free to ask here or post a question in the general forum and I am sure an expert will be along to help answer questions.
Edit: Here is a commentary sent to me via PM...
"When the M1a first came out, not Devine's as I recall, but the people after Elmer, many of the receivers, maybe all of them, had the firing pin cam cut in the wrong place. The pin would catch and fail to go fully into battery. At that time, it was common practice to round off the matching area on the Firing pin.
It was not unusual to see rifles where the cam area was gouged out from this misalignment. Other Brand receiver's had the same problem only worse.
It was suggested that a non chrome pin should be used thus transferring the wear to the pin only. I think this helped. I did see several rifles that fired on going into battery from worn cam areas. There was NO correction for this situation short of a new receiver.
There is a special gauge to check another situation, called Bridge advancement, this was during the M1 days. The bridge can and has advanced over years that produces slam fires. Ted Brown has the only gauge that I know about."