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Posted: 4/25/2006 5:36:14 PM EDT
I know that ARs fire from a closed bolt, but what exactly is the difference in operating principles between the two? What are the advantages and disadvantages of each? Thanks.
Link Posted: 4/25/2006 5:53:39 PM EDT
[Last Edit: 4/25/2006 5:54:06 PM EDT by CK1]
Quick and dirty explanation:

Closed bolt is more accurate, less moving parts as the bullet is fired, more consistent lock up, will contain high pressure loads very well.

Open bolt is hella simply and fast to cool, very easy to modify into full auto, thus the ATF will ream your ass sore for it. More commonly seen in blowback sub machineguns.
Link Posted: 4/25/2006 6:05:28 PM EDT
Closed bolt: When you pull trigger, the hammer hits the firing pin, causing the primer to ignite (ar-15, etc)
Open bolt: Pulling trigger results in the bolt going foward. The firing pin goes foward automatically when the bolt is all the way foward. (m60, etc)
Link Posted: 4/25/2006 6:10:36 PM EDT
full auto's are sometimes open bolt, SAWs M240s M60s and one particular model of the Thompson SMG (though I don't recall which) are all open bolt fired weapons.
Link Posted: 4/25/2006 6:12:04 PM EDT
[Last Edit: 4/25/2006 6:13:36 PM EDT by olds442tyguy]
Open bolt has a fixed firing pin, where as closed bolt is hammer struck.

Say you had an open bolt handgun. When you fired a round off, the slide would lock back as if you had just shot the last round. When you pulled the trigger, the slide would release and the fixed firing pin would strike the primer as the slide came forward.
Link Posted: 4/25/2006 6:33:47 PM EDT
As I recall, the primary reason for an open-bolt action on sub- and machine guns is so that when you let go of the trigger, the chamber is empty & the bolt back; that way, after firing for extended periods, the risk of ammo "cook-off" is greatly reduced.

/TCP
Link Posted: 4/25/2006 6:36:34 PM EDT
Open bolts designs are most common with Sub machine guns and Belt feed weapons due to their Cyclic rate and the heat generated by the rate of fire. Open bolt designs keep a round out of the chamber until the firing sequence is intitated thus reducing the chance of a chambered round from cooking off in a hot barrel/Chamber

The Only Large Caliber MG that fires from a closed bolt is the M2 BMG.
Link Posted: 4/25/2006 7:10:18 PM EDT
The Thompson M1921/28 series and M1/M1A1 series of submachine guns all fired from the open bolt.
Link Posted: 4/25/2006 7:21:30 PM EDT
[Last Edit: 4/25/2006 7:31:31 PM EDT by bigbore]
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