Bobbing an ar hammer (make speed hammer)

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  • REDLINE83

    AURIBUS TENERE LUPUM
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    33   0   0
    Sep 9, 2015
    879
    18
    Northshore
    Who has done it? Putting lower springs instead of mil spec and want to maintain reliability. Can you do it to a nickel boron coated hammer?
     

    991GT3

    Well-Known Member
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    0   0   0
    Jan 27, 2015
    264
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    Baton Rouge, LA
    Why not purchase a Geissele SSA and have a SAFE, RELIABLE trigger?

    If you don't want to spend $200 then look into ALG DEFENSE (Bill Geissele's wife's company). I think their trigger is $65.

    Mil spec triggers are MIM which means once you grind away the surface it's relatively soft. I'd not recommend it.


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    noob

    enthusiast
    Silver Member
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    41   0   0
    Mar 18, 2008
    4,284
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    New Orleans
    the super 3 gun and CMC's single stage are very quick triggers. They hyperfire company has had a bunch of sales on their triggers (for ~90 bucks) but haven't been around long enough for me to want to test out their products. I have triggers from geissele, larue and CMC and like them all, and each one of them have their perks as to why to use them
     

    Magdump

    Don’t troll me bro!
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    163   0   0
    Dec 31, 2013
    9,396
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    Hammond, Louisiana
    As to the question, sure, you can chop off some metal, but you may run into some problems. When modding the mil spec fire control group, there are things that help and things that probably make it less reliable. I've never had issue with the JP 3.5lb spring set (yellow) on a mil spec group. I've used that setup on 5.56, .300AAC and 9mm. I hone and polish them and use the right grease. The hammer needs a certain amount of weight to strike the firing pin hard enough, especially when using lighter weight springs. It's called inertia. The mil spec group has been greatly improved on over the years, but such drastic mods are better left to the pros.
    There's nothing especially fast about a mil spec group. The pull is long compared to many aftermarket triggers and the reset is nothing extraordinary. But they work. Honed, polished and fine tuned, they can be pleasant enough for the cost. Unless I'm building a precision rifle for some long range accuracy, I find anything else unnecessary.

    But ya know what? As cheap as those sets are, try it and see. I might even have a couple hammers I can donate. I never wanna stand in the way of innovation, as long as it don't turn into disaster, lol.
     

    John_

    Shooter
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    21   0   0
    Nov 23, 2013
    3,451
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    Hammond, LA
    ^^^ listen to the man above. Whatever fractional reduction in lock time you gain by significantly bobbing the AR 15 hammer, you lose in inertia energy transferred via the firing pin, and onto the primer itself.

    Hammer mass + spring tension = stored energy
     

    Saw

    Well-Known Member
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    18   0   0
    Oct 6, 2008
    388
    16
    New Orleans
    Kinetic energy = 1/2 mv^2

    Less mass and greater velocity (same spring pressure right?) could actually give you slightly greater kinetic energy. The Brownells' bobbed hammer claims 50% less lock time that would translate to considerable increase in final velocity^2. This all would assume bobbed hammer compared to stock hammer (heavier) with same springs.

    The real question is whether that setup (lighter spring/lighter hammer)has enough KE compared to stock for reliable ignition. The interwebz suggest yes, so it may be worth 500-1000 rds to see. I'm thinking about doing it with my 300 BLK to see what is the best you can get a stock trigger with a $6 spring, polish, lube, etc. Range toys and whatnot.

    I haven't done it yet, but a Drexel, file, sandpaper, and some cold blue should be a 20 minute project. Reversible with a new ~$10 hammer.
     
    Last edited:

    John_

    Shooter
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    21   0   0
    Nov 23, 2013
    3,451
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    Hammond, LA
    And I agree, this would be a cheap experiment only costing at worst a hammer or two and your time. But the biggest obstacle I see is how does the average enthusiast measure lock time accurately on an AR 15? Surely you would need to measure and record stock or baseline lock time. Then do ur mods and in the end re-measure lock time to establish a change. And we're talking about milliseconds. How would even a gunsmith/small shop accurately measure lock time in a modern smokeless propellant firearm? You would need precision machinery to correlate the trigger breaking to the report of the round, or exiting the muzzle.

    Without a baseline or a method to precisely measure a specific weapon's lock time its pretty much a crap shoot. Sure you can grind on the hammer incrementally until you experience light strikes/failure to detonate the primer. Then go back a bit on a second hammer, but how do you really know what impact you have made on lock time? How do you really know if you have executed anything worthwhile?

    And I'm not trying to be argumentative on this topic, I just don't see how the average guy can measure and quantify a change concerning lock time. Best left to the trigger mechanism manufacturing professionals imo, and then many times I really wonder about their claims. "speed hammer" or substantial or meaningful lock time improvements. But it does sell aftermarket parts.
     

    Saw

    Well-Known Member
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    18   0   0
    Oct 6, 2008
    388
    16
    New Orleans
    I agree that it would be nearly impossible for the average joe to measure lock time. I don't think it matters. I think you buy the lighter spring set in hopes to decrease trigger pull weight (along with polish, lube, etc.). I think you bob the hammer to look like every other speed hammer in hopes of creating a system that gets enough energy to the primer every time for 100% reliable ignition. Build it and try it out for a few hundred rounds of your ammo (really primer right?) of choice and call it a win for a few $.

    That is my plan for my 300 BLK with stock mil spec trigger group.
     

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