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1/25/2018 7:38:29 AM
Posted: 9/19/2002 12:32:14 PM EST
A friend and myself were having a disscussion on open and closed bolt weapons and how they fire. What we came up with is that a open bolt "slam fires" the round, now I have always heard this is dangerous, so how does it work? I have heard tons of people talk of how there semi when FA by the firing pin sticking or the disconnect not working right and the hammer following the bolt back.
If memory serves me right most SMG's are open bolt.
I was at the range the other day and decided to rent a MAC-10 FA (let me just tell you that thing cycles like a bat out of hell!!) and we compared the FA vs Semi(open bolt) and they are almost identical(buddy is range master).
Just thought I could get everyone elses opinion.
Link Posted: 9/19/2002 1:30:39 PM EST
I would explain it but I would probably get another email telling me not to be so descriptive.
Link Posted: 9/19/2002 4:10:05 PM EST
I'm NOT talking about anything illegal here, I just didn't know how a open bolt weapon fired and found it interesting that the same way it works is a design that could be dangerous if the round were to fire out of battery. Whats to say that as the round is picked up from the mag that some how the primer is struck from the protruding firing pin.
Link Posted: 9/19/2002 4:13:56 PM EST

Originally Posted By ZMan:
What we came up with is that a open bolt "slam fires" the round, now I have always heard this is dangerous, so how does it work?

The blowback operated submachine guns you mention are designed to 'slam fire'. It fires from an open bolt. The firing pin is a bump on the bolt, there is not separate firing pin as such.

When the bolt slams shut the round fires. Since the bolt is not locked, the impulse from firing the round 'blows back' the bolt. The reason its safe is that the mass of the bolt is designed to be heavy enough that by the time it can move back, the bullet is already out the barrel and the pressure is at a safe level.

A rifle like the AR15 has much higher pressures in it than a 9mm submachine gun, so the bolt on an AR15 locks before a separate firing pin can set off the round. It would be theoretically possible to design a blowback system for the 223 but the bolt would have to be MUCH heavier than it currently is. The resulting rifle would be too heavy.

(Warning...I'm not a real gun designer..but I did stay in a Holiday Express once)

Hope this helps....ECS
Link Posted: 9/20/2002 10:50:18 AM EST
[Last Edit: 9/20/2002 10:51:59 AM EST by TonyWilliams]
This may be a bit OT, but certain other military weapons (apart from SMGs) were designed ONLY to "slam fire". The reason for this is that they fired as the bolt was still moving forward, so the recoil first had to stop the bolt before it could start pushing it back again (this allowed a much lighter bolt and faster cyclic rate). They were known as "advanced primer ignition blowbacks" and included all of the WW2 Oerlikon 20mm cannon and anti-tank rifles, and the German WW2 20mm MG-FF and 30mm MK 108 aircraft cannon.

Oh yes, the WW1 Lewis LMG was also a "slam-fire" weapon, which is why it couldn't be synchronised to fire through the propeller disk - the lock time was too long.

Tony Williams
Military gun and ammunition website: http://www.quarry.nildram.co.uk
Discussion forum at: http://forums.delphiforums.com/autogun/messages/
Link Posted: 9/20/2002 2:38:20 PM EST
Link Posted: 9/21/2002 7:27:12 PM EST
Scarey !!!

It would seem that more KB would happen with the AR15. Scarey to think that if the firing pin jams in the protruded position from sand, or other junk, that one's AR15 would self-disassemble in a quick fashion.

And, I use Federal primers (aka, soft primers). Perhaps I should think about switching to CCI primers.
Link Posted: 9/21/2002 8:55:58 PM EST
Link Posted: 9/21/2002 9:19:05 PM EST

Originally Posted By dennysguns:
Chamber a round in your AR/M16 next time you are at the range and then unload that round. You will see a mark on the primer where the firing pin bounced.

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