AR15.Com Archives
 3 Round burst
xmission  [Team Member]
5/27/2010 6:36:45 AM EST
I can see how full auto works, but how does 3 round burst work in military rifles?

Is there some sort of cog that advanced with each shot, and then it resets at the end of the burst?

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freeflow  [Team Member]
5/27/2010 3:39:26 AM EST

Originally Posted By xmission:
I can see how full auto works, but how does 3 round burst work in military rifles?

Is there some sort of cog that advanced with each shot, and then it resets at the end of the burst?


trap.
Hector45  [Team Member]
5/27/2010 3:44:16 AM EST
I too always wondered this.
timpryor  [Team Member]
5/27/2010 3:51:16 AM EST
Magic

but seriously
Arfcom knows all
manual_c0cker  [Member]
5/27/2010 3:51:28 AM EST
Here you go
osprey21  [Team Member]
5/27/2010 3:52:19 AM EST
http://www.ar15.com/content/guides/function/burst/


1saxman  [Member]
5/27/2010 4:18:28 AM EST
Originally Posted By xmission:
I can see how full auto works, but how does 3 round burst work in military rifles?

Is there some sort of cog that advanced with each shot, and then it resets at the end of the burst?



Yes.

CONKLE73  [Team Member]
5/27/2010 4:29:29 AM EST
Part number (3) in the figure below is the burst cam.
It allows the hammer to fall 3 times before it is held for reset when the trigger is held to the rear.



kcolg30  [Team Member]
5/27/2010 7:20:34 AM EST
Originally Posted By xmission:
I can see how full auto works, but how does 3 round burst work in military rifles?

Is there some sort of cog that advanced with each shot, and then it resets at the end of the burst?



Cozmo or Spacely
CAR-AR-M16  [Team Member]
5/27/2010 9:19:59 AM EST
Originally Posted By kcolg30:
Originally Posted By xmission:
I can see how full auto works, but how does 3 round burst work in military rifles?

Is there some sort of cog that advanced with each shot, and then it resets at the end of the burst?



Cozmo or Spacely


Cozmo made cogs, Spacely made sprockets.

F14ADC  [Member]
5/27/2010 10:35:16 AM EST
Originally Posted By CAR-AR-M16:
Originally Posted By kcolg30:
Originally Posted By xmission:
I can see how full auto works, but how does 3 round burst work in military rifles?

Is there some sort of cog that advanced with each shot, and then it resets at the end of the burst?



Cozmo or Spacely


Cozmo made cogs, Spacely made sprockets.



Actually it was Cogswell that made cogs.
ETA: Cosmo was Spacely's first name.
regards,
Ralph
USMCRONIN  [Member]
5/27/2010 11:19:51 AM EST
some NATO 3-rd burst equiped rifles would reset each time the trigger was pulled so each burst was 3-shots (provided that ammo was there)
US 3-shot bursts do not, if you release the trigger before 3-shots are fired then the next trigger pull the remaining # of 3 is fired.
they are sort of like a rachet, each bolt cycle turns the "cam" one position, then after 3 it resets.
xmission  [Team Member]
5/28/2010 10:49:32 AM EST
Thanks guys. Your answers tell all.

I wondered how it could work simply, without adding a whole lot of stuff in that little hole.
xmission  [Team Member]
5/28/2010 10:51:55 AM EST

Originally Posted By USMCRONIN:
some NATO 3-rd burst equiped rifles would reset each time the trigger was pulled so each burst was 3-shots (provided that ammo was there)
US 3-shot bursts do not, if you release the trigger before 3-shots are fired then the next trigger pull the remaining # of 3 is fired.
they are sort of like a rachet, each bolt cycle turns the "cam" one position, then after 3 it resets.

On the US stuff, does turning the selector to semi reset the cam, or does it fire the remaining number when you go back to auto again?


Circuits  [Team Member]
5/28/2010 11:13:42 AM EST
Originally Posted By xmission:
On the US stuff, does turning the selector to semi reset the cam, or does it fire the remaining number when you go back to auto again?


It's the burst disconnector which drags the burst cam to each new position, and a standard 3rb FCG engages the burst cam on each cycle regardless of the position of the selector, so a 3rb group is constantly advancing. It might or might not end up starting on a 3-count. Example: you fire 2 of 3 rounds in a burst, then switch to semi for two shots, then back to burst... Your next shot will be 2 rounds.

The 4pos groups operate differently, in that the burst hook doesn't contact the burst cam in auto, but does in semi and burst. If you switched from burst to semi, it would work like the 3rb group does, but switching burst to auto and back would not change the cam's position at all. Fire 2 of 3 in burst, switch to auto for any number of rounds, then back to burst, and you'll get the remaining 1 shot of the original burst next time you fire.
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