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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."
 

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This information really helps one to understand their rifle all the more, and to know what areas to examine for wear on a routine basis.

As usual: excellent explanations coupled with high def. picture-grams for clarity. Thank you, sir!

DI2
 

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Thanks Tony, Though I have heard it explained, this is the first time I have seen an actual photo display outlining the Bridge in action. Very Well Done, Clear, Concise and even understandable to old fogy as myself!
 

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Good job Tony....your usual excellent informative post. We are all proud to have you with us. MCORPS1
 

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I always use a parked firing pin, NOT chrome - less wear on the safety bridge
JD, isnt there the same wear on the metal after the parkerizing wears away? I am confused. Chrome is that much harder/durable?
 

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Thanks Tony, I hope this turns into a "sticky" !
 

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Discussion Starter · #10 ·

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I always use a parked firing pin, NOT chrome - less wear on the safety bridge
and I always use chrome because it is "slicker" and will prevent damage to the safety bridge. I also always dab a bit of grease there to help "slide it in"GITEN
 

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These type of informative post are alway appreciated.MCORPS1
 

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I am with shadow on the chrome pins and a dab of grease. Although it's harder Crome has less surface friction. Is there any hard and fast rule? I doubt it, just personal preferance
 

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Tony asked me to look at this thread and provide some information about types of firing pins and modifications.

First, I would like to mention I wrote about safety bridge problems in posts numbers 2 and 3 of another thread.. So I don't have to type that all out again, if anyone is interested, please check here:

http://www.m14tfl.com/upload/showthread.php?t=62376

I have seen firing pins that were way, WAY over modified to allow the tail of the firing pin to cam around the notch in the receiver and thus allow the rifle to fire. I do not agree that's the way to correct the problem. When you round the firing pin tail that much, you break through the hardened outer skin of the firing pin and the tail is going to wear out much faster than normal. Most of the time, you can polish a burr or sharp edge off the notch in the safety bridge to fix this problem and that's the correct way to fix it. That keeps the hardened outer surface of the firing pin intact and allows the firing pin tail to stay serviceable much, MUCH longer. When you heavily cut through the hardened outer skin of the firing pin, you are just asking for unintentional full auto firing in the not too distant future.

OK, have to think about a couple other things, so I will stop here and post this information, then go on in another post.
 

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OK, as to a non chromed firing pin supposedly not wearing as much on the receiver bridge as a chromed firing pin - got to admit in 37 years of working on M14's, that's the first time I ever heard that one. (Gee and I thought I had long ago "heard them all." Grin.) Folks, that is a question I never thought to ask the Engineers or folks at H.P. White Laboratory about.

A G.I. non chromed firing pin wears out and breaks FAR FASTER than a chromed firing pin, but the place they usually crack or break is around the center of the pin and not near the tail (same thing is true for the chromed firing pins, btw). This I did ask about and was told that's why they went with the chromed firing pins. I can also see the chrome provided better lubricitiy and that would have accounted for a little less wear on the receiver bridge. I have seen maybe 5 cracked chromed firing pins in my career out of the thousands of firing pins I've inspected.

Since G.I. receivers would go for hundreds of thousands of rounds before they wore out, even chromed firing pins cracked or wore out before the receiver was toast. This receiver life was figured with chromed firing pins, so I don't think we have to worry about chrome firing pins wearing out the saftey cam in a properly hardened civilian receiver.

I do know I will only use a non chromed firing pin in a G.I.or commercial M14 when a G.I. chrome firing pin is not available because the chrome ones last so much longer.
 

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P.S. the chrome also keeps the tip of the firing pins in much better condition for much longer and that's another reason the M14 firing pins were chromed.

After WWII, they went with flash chroming just the tips of the firing pins and the "nose" of the bullet guide to make these points wear longer. However, this was not something they demanded be done and you don't find that on the 1950's production M1 Garands of IHC, HRA or even much (if any) of SA production.
 

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From the PM to Tony: "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."

I and most folks who do a lot of work on M1 Garands have one of these gages. They were only used by the 5th Echelon Depots, so there were never many made. A whole bunch of M1 Garand Armorers in the day never saw them except for the pictures in the Technical Manuals.

However, to my knowledge they never had such a gage for an M14. It may be because the M14 only lasted so long as the standard issue service rifle and they never had to develop such a gage when more worn M14's came along.

Ted Brown brought it to my attention that in Rock Island Arsenal's rebuild standards for the M14, they actually ALLOWED the center of the receiver bridge to be cracked or even broken all the way through and be rebuilt that way. It also said bolts could be cracked or chipped. I pulled out my copy of the manual and danged if he wasn't correct! This is another case of something Rock Island "safety certified" that the Marine Corps NEVER allowed. I could see an M14 with a safety bridge broken through the middle flexing to the point it would allow the firing pin not to be engaged by the safety bridge and unintentional full auto firing be the result.
 

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and I always use chrome because it is "slicker" and will prevent damage to the safety bridge. I also always dab a bit of grease there to help "slide it in"GITEN
Didn't think of it that way, I'm a little gun shy i guess - i had a Fed Ord M14, all GI parts & shot pretty good but the receiver bridge was WELL worn & finally got to the point that i didn't feel safe firing it, i still have it & one of these days I'm going to weld up the bridge & lug it - I have a new idea for a lug design but I'm reluctant to try it on a "good" receiver until it's been tested on my beater Fed Ord!
 

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I love to read these "snowballing" informational threads.

Seems like welding up, then re-machining would be completely acceptable. Why is this not the fix? If you add a lug or two to a receiver, it's the same difference to heat treatment right?
 
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