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Posted: 10/21/2008 1:29:16 PM EDT
I have a couple of questions about the design of the AR15 hammer.
First, here is a picture taken from right here on arfcom, showing the "standard" modifications between these two parts.  Note that there are two primary changes. First, a "notch" has been cut in the face of the hammer. Second, the "hook" has been removed from the "tail" of the hammer. The following illustration highlights the area removed for the notch in red, and the remainder of the tail in grey.  So, here are my questions. First; what is the reason for removing the "notch". My understanding is that it is to prevent the hammer from riding the bolt down in the event that the disconnector fails, but I'm not certain. Second, why is the remainder of the tail shown in gray retained. I can understand that if you are starting with M16 parts then you might only machine off the minimum required. But if you are building a semiautomatic trigger from scratch, why keep this material? Would there be anything wrong with the third hammer I've illustrated, other than the fact that the "anti-hammer-follow" design has been compromised? |
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Posted: 10/21/2008 1:39:56 PM EDT
[#1]
The main difference is one is Auto the other is not. That rear hook is the hook that the auto sear catches as the bolt carrier group slides back. As far as the the notch in the top I have no idea but I am sure it makes it more difficult for people to convert to auto. Use of the same material? Why change when it has held up so long and is tried trued and tested
The problem I can see with your modified hamer is there is going to be a change in weight and balance which may cause light hits or even harder hits. A trigger is not really a part to mess with it can be a very dangerous test. |
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Posted: 10/21/2008 1:42:28 PM EDT
[#2]
That is correct. |
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Posted: 10/21/2008 1:45:27 PM EDT
[#3]
It was put there to produce a symptom called "collar catch". If you used a M16 firing pin with a unshrouded carrier, all you could find along time ago, the collar on the M16 firing pin would catch on that notch thus stopping the function of the weapon.
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Posted: 10/21/2008 1:47:34 PM EDT
[#4]
one reason to keep the hook as stated in the previous post is weight/mass. The amount of energy striking the firing pin is a balance between the speed of the hammer and the mass with some consideration for the distance between the point of rotation and the center of mass. You can use lighter springs to get a lighter trigger pull but with the hook, the hammer has enough mass that the springs MIGHT not produce enough velocity for reliable ignition. A fairly common modification with light springs is to cut the tail off of the hammer. The extra spur on the first hammer has something to do with automatic function with an auto sear, but I don't know enough about it to elaborate. On a 9mm build the notch is actually dangerous as it can bind on part of the bolt carrier rendering the gun inoperable and difficult to disassemble.
ETA: I chimed in a little late on the notch, please see above for better informed answers. |
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Posted: 10/21/2008 1:52:39 PM EDT
[#5]
At time's the area in grey is removed to prevent the "tail" from hitting the disconnector. And causing hammer follow. Also lighter hammer's reduce lock time. Both of these mod's are seen most often in match rifle's. Don't try this at home unless you are very good and very informed on AR15 trigger's. The only Hammer follow "Machine gun's" I have seen came from broken disconnetor's or improperly timed disconector's. Luckily none resulted in full mag dumps. Also if your rifle ever fire's when you release the trigger. Check the disconector
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Posted: 10/21/2008 1:55:15 PM EDT
[#6]
That would be almost exactly the same as JP's Speed Hammer  JP's design will not work with mil-spec pins and is made from some uber-high tech process, but is primarily just a pared down hammer for decreased lock time and increased accuracy potential due to less moving mass being flung about inside the receiver. Some have cited hard primer strikes, to the point of punctured primers in rare cases. ETA: As stated by YoteSlayer69 above, really only useful in precision/match rifles. |
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Posted: 10/21/2008 1:59:00 PM EDT
[#7]
I have a JP trigger in my carbine. With a standard AR hammer and thier tacticle spring kit.4.5 pounds break's like glass awesome trigger!
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Posted: 10/21/2008 1:59:27 PM EDT
[#8]
The answers about the mass of the hammer helped me think this through more. It seems that the "tail" serves no functional purpose other than to provide mass. That mass is not needed - if the entire trigger/hammer system has been tuned not to need the mass. Here is one "low mass" hammer I found online - it looks almost exactly like what I drew.
Don't worry, I'm not going to go hacking the tail off of my hammer. I just couldn't understand why that tail would be engineered there in the first place. |
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Posted: 10/21/2008 2:06:06 PM EDT
[#9]
Remember all AR15 part's started as M16 parts manufacture's modify them to semi auto spec's with as little labor as possible. It's when you get into custom rifle's that "MIL Spec" goes out the window and all sort's of thing's crop up to improve on the original design. Just be careful stick with known good supplier's. And when in dought ask.
 . Buy some book's and study em too!!
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Posted: 10/21/2008 2:14:33 PM EDT
[#10]
...but it only works if you are using an unshrouded bolt carrier, like the one on the right. 
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Posted: 10/21/2008 2:27:19 PM EDT
[#11]
I think the one on the left is a standard M-16 bolt, and the one on the right is a standard AR-15 bolt, but I'm not sure about the one in the middle. It can't trip a sear, but it doesn't have the hammer follow mods. What is it? |
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Posted: 10/21/2008 2:33:06 PM EDT
[#12]
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Posted: 10/21/2008 3:04:26 PM EDT
[#13]
What is the advantage of this hammer? |
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Posted: 10/21/2008 3:15:43 PM EDT
[#14]
the one on the right is a COLT half circle AR15 carrier |
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Posted: 10/21/2008 3:19:57 PM EDT
[#15]
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Posted: 10/21/2008 3:28:28 PM EDT
[#16]
The one in the middle is a semi auto carrier. Colt's unshrouded half circle carrier is the one on the right. |
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Posted: 10/21/2008 4:02:47 PM EDT
[#17]
Who made the one in the middle? I thought most SA carriers had the milling to prevent the hammer following the bolt if the disconnector failed? |
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Posted: 10/22/2008 2:35:44 PM EDT
[#18]
The one in the middle is a Bushmaster carrier. |
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Posted: 10/22/2008 2:51:06 PM EDT
[#19]
All of my semi carriers (CMT) are shrouded like that. |
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Posted: 10/25/2008 12:35:52 AM EDT
[#20]
Stag now furnishes un-notched hammers in their lower parts kits. I have been after them for a couple of years to kill of the notches.
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Posted: 10/25/2008 12:41:09 AM EDT
[#21]
Funny, I remember years ago a review of a Stag kit here, and it had a polished, un-notched hammer. By the time I got their kit (from you!) it was back to a "standard" AR hammer. Good work making them finally understand! 
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Posted: 10/25/2008 12:41:26 AM EDT
[#22]
What do you have against the notches? |
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Posted: 10/25/2008 12:49:19 AM EDT
[#23]
The notch can get hung up on an unshrouded firing pin and cause the jam from hell. Un-notched hammers are smoother operating and also weigh a tad bit more. The notch serves no purpose and creates only problems. I can only guess most companies make them with the notch because Colt started it back in the day and most of them just did it because Colt did it. Gene Stoner did not design the M16 with a notched hammer. |
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Posted: 10/25/2008 12:53:09 AM EDT
[#24]
or high shelf lowers.  
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Posted: 7/24/2009 2:54:06 PM EDT
[#25]
Good info here.
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Posted: 7/24/2009 3:19:42 PM EDT
[#26]
Primers are specified to the energy it takes to set them off. Energy is solely determined by the spring force along the arc length of the hammer, not the mass of the hammer or the polar moment of inertia of the hammer (mass distribution).
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Posted: 7/24/2009 4:55:59 PM EDT
[#27]
tag. |
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Posted: 7/24/2009 7:31:37 PM EDT
[#28]
My buddy and I both ordered the JP Rifles yellow lightweigt spring kit. I cut my hammer down to the low mass profile, he did not. My rifle functioned perfectly without a hiccup. His never fired. Appears that the weight of his full profile hammer retarded the speed enough with the light springs to prevent the primers from going off. His rifle was flawless until he changed the springs.We won't know for sure until we rework his hammer and check everthing else. We'll see...
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Posted: 7/24/2009 7:50:20 PM EDT
[#29]
Quoted:
Primers are specified to the energy it takes to set them off. Energy is solely determined by the spring force along the arc length of the hammer, not the mass of the hammer or the polar moment of inertia of the hammer (mass distribution). I think the hammer strike results in an impact load on the firing pin, this impact load does indeed depend on the mass of the stricking object ( in this case the hammer) as well as the ratio of the firing pin mass to that of the hammer. |
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Posted: 7/24/2009 8:37:19 PM EDT
[#30]
Quoted:
Stag now furnishes un-notched hammers in their lower parts kits. I have been after them for a couple of years to kill of the notches. Thank god. |
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