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Posted: 12/31/2001 3:39:41 PM EDT
I hear these used alot. What is the difference?

Closed bolt like on a Tec, and open like on a Mini, or am I way off?
Link Posted: 12/31/2001 3:49:47 PM EDT
The terms describe the point from which the firearm is fired.

Closed Bolt: The bolt is closed on a chambered round. When you squeeze the trigger, a hammer (usually) is released to strike the firing pin, which ignites the cartridge. On a semi auto, the case is then extracted, a fresh cartridge is chambered and the bolt comes to rest, as before, on a chambered round. The AR15/M16, MP5, and a boatload of other rifles and pistols use this method.

Open Bolt: At the point of firing, the bolt is to the rear (open). When the trigger is squeezed, the bolt is released to strip a round from the magazine/belt and insert it into the chamber. As part of this same cycle, the hammer is then released to strike the firing pin and fire the round. The conclusion of the cycle is the extraction of the case and the return of the bolt rearward. A lot of belt-fed support weapons, like the M60, operate this way. This ensures that the chamber is always open prior to and after firing, so that it can cool (and so that a round cannot cook off under extreme heat). It's not the most accurate method, because the movement of the bolt can be significant.
Link Posted: 12/31/2001 3:53:44 PM EDT
Cool. Thanks. That explains it.
Link Posted: 12/31/2001 5:12:48 PM EDT
Link Posted: 12/31/2001 6:29:24 PM EDT
The bad thing is that with open bolt semi-autos is that they are easy to be converted to full-auto.
Link Posted: 12/31/2001 6:35:08 PM EDT
AR18,
Aren't semi UZIs required to be closed bolt? I remember something in the late 80s about UZI semis having open bolts, and the ATF required mods for legality?
Link Posted: 12/31/2001 7:48:17 PM EDT
All semiauto weapons are now required to be of closed bolt design. The old MAC's used to be open bolt and had to be redesigned to fire from a closed bolt.

Open bolt semis are pretty rare. The only open bolt guns I have ever seen have all been machineguns. Though I admit I might have seen a MAC or two, but didn't pay enough attention to notice.
Link Posted: 12/31/2001 8:32:35 PM EDT
The early imports of the Model A UZI are legal to own. IMI had to redesign the UZI to the Model B standard. AFT found that the Model A like the MAC can be easily modifiy for full-auto. The Model B is the more common semi-auto UZI because of the close bolt design.
Link Posted: 12/31/2001 10:07:02 PM EDT
Actually if I remember correctly the M60 and the M249 SAW do not have hammers. As the bolt closes and rotates to the locked position a fixed firing pin detonates the primer on the cartridge.
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