|
Basically firing open bolt - MAC10 or 11 full auto, Sten, etc is ready to fire with the bolt locked open. Pulling the trigger releases the bolt, as the bolt moves forward it strips a round out of the mag, chambers and fires it just as it comes into battery. Most that function this way have a fixed firing pin. When the trigger is released the bolt catches on the sear as it is blown back after the last round fired.
Firing closed bolt - most semi auto or select fire rifles, carbines, semi auto pistols, etc. have a floating or seperate firing pin that the hammer strikes to drive forward to pop the primer. The bolt has to be fully closed (in battery) to fire. Most have a disconnect that prevents the hammer from releasing until the bolt is fully locked in battery. The select fire rifles have a forward or secondary disconnect that releases the hammer just before the bolt is in battery - the timing is such that the hammer is released before the bolt is actually locked but in the millisecond(s) that it takes for the hammer to move forward to contact the firing pin the bolt has also the time to lock in battery. In other words in a select fire weapon, if semi is selected the sear catches the hammer each round - just like any semi auto firearm, and you have to release the trigger to allow the disconnect to reset and pull the trigger again for the next round. In auto the bolt basically releases the hammer each time until you release the trigger and allow the sear to reset.
And it's about as simple as that!
Advantages/disadvantages? That's an engineering discussion really? In my opinion open bolt mechanisms, especially some of the older ones can be of marginal safety. The Stens are a great example of what I mean about that. If you look around and research the history of the Sten's use by the British military, you can find numerous accounts and stories about them running out a full mag with no control and no stopping. According to a lot of the prints I seen of their trigger group and simplistic construction there doesn't seem to be much in the way of basic safety features. The MAC10/11 design seems to be more stable but I've never seen much in the way of prints or parts of their inner workings. I've had opportunity to fire MAC style subs several times over the years and never had anything wierd happen. Mechanically I think that closed bolt operating systems are safer. Also, I don't know of any open bolt mechanism semi auto (non class III) firearms.
__________________
The Second Amendment, it ain't about DUCK HUNTING!
I feel more like I do now that I did when I first got here!
| 
