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Posted: 8/6/2004 5:15:05 PM EDT
| My current understanding of AR firing pins is that they are "free-floating." How do they work without a spring to return them to the rearward position? Wouldn't the addition of a spring make them "safer?" Is there a way to add a spring? I'm a complete noob, and since I've got a bunch of AR parts on the way for my September 13th build (I can build on the 13th, correct?), I'm starting to ask questions about why and how things work. Thanks! |
Colt No. 1 design had one in an attempt to solve the slam fire problem early on. They investigated the firing pin energy and primer sensitivity. Later they concluded that all that was needed was 'harder' primers. |
I've fired a pre-ban AR before, and didn't have any problems with it. However, that was on a range. How well does an AR hold up out and about with a round in the chamber? I assume that once the bolt's down and the safety's on, that pin doesn't have enough energy to fire a round off. I was just curious as to how the firing pin returns to it's rearward position without a pin to compress. 
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I can't say for certain due to lack of X-Ray vision durring operation but it would seem that it might return to the rear or it might not depending on the position of the rifle, and the bounce it makes off the chambering primer strike. The design is that the pin doesn't have enough energy to touch off the primer on it's own when the bolt slams forward. It has to get whacked by the hammer to do that. Forward or rearward the hammer hitting the FP will cause the primer to fire and so the spring is not nessisary, Personally I'd prefer it had one. I still don't like the dings on the primers of chambered rounds but in over 2000 rounds I have never had a slam fire and I never use anything else than just popping the bolt-catch. I'd still feel better with a spring. |
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I've seen the early colt spring design, and I think changing it to free floating was the way to go, despite the superficial primer dings of a ff pin. If you consider the location of the spring on the early pin(somebody have a pic?) and the AR/M16/M4 direct gas impingement system, a large portion of carbon and crud gets blown into that exact location where the spring sat in the early pin. Now picture all that rock carbon getting caked in between the spaces of the spring, and constant compressing and decompressing untill it's finally caked to the back causing a faliure to fire, or caked forward possibly causing a slam fire? |
It doesn't return anywhere, it floats. All the way forward, all the way back or somewhere in between it doesn't matter. The hammer smacks it and then and only then will it hit the primer (assuming a properly seated and proper primer) hard enough to cause it to fire. |
It strikes the primer (not moving fast enought to cause ignition). Since the pin doesn't have enough inertia, it doesn't 'resist' changing direction well enough to fire the round, and is pushed back into the carrier.... |
Armalite AR10s do have a spring loaded firing pin. Why? Because the firing pin is larger, has more mass, and might have enough inertia supplied energy to set the primer off when the bolt slams into battery. |
Sorry, missed the whole AR10 line in this thread. 
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Actually, the Ti firing pins are LESS likely to cause a slam fire because of their lower mass. F=MA. Force = Mass x Acceleration Less mass = less force = less likely to detonate primer. A firing pin can go no faster than the bolt/carrier. Both standard and Ti firing pins would attain the same velocity during firing. The problem with the Ti pins is they are brittle and prone to breakage. Definitely NOT recommended. In any event, slam fire in AR-15's is a non-issue. |
I know! The 10s is part of the system. The fact that the 10 has the spring loaded pin also helps illustrate why the 15 doesn't. |
Thanks for the input. I never understood how the pin returned rearward, but it seems like common sense. 
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