Firing from the open bolt?

skeetgunner

skeetgunner

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What effect does fireing from the open bolt have on accuracy and trigger pull? I imagine that the trigger pull would be heavy, and the sudden shift in mass would be detremental to all but mounted guns.

Am I right?
 
The only weapons that I've fired from the open bolt would be the C9 and the C6 and because they are machineguns intended to cover an area with fire, any accuracy lost is negligable and inconsequential (even just with a bipod). The same can probably be said of the older subguns, they were designed to be fired full auto from close quarters and even with an open bolt are quite suited for this application.
 
It depends on the specific model; in some firearms, there's a very noticeable (and sort of disconcerting) pause between pulling the trigger and cartridge ignition, during which you can actually feel the whole firearm "slump" forward. I'd put the Sterling/C1, the Sten, and especially the M3/M3A1 in that class. With others, it's barely noticeable, like the UZI; with the 3rd-generation-style bolt that overhangs the barrel, you don't really notice much of a shift in balance.
 
The bolt and bolt carrier assembly in my Bren probably weighs 2-3 pounds. When you pull the trigger there is a delay as the mechanism slams forward, a la flintlock. Even though it weighs 24 lbs (aprx) and is on a bipod, you can definitely notice the gun moving before ignition. I actually offset my front sight a bit, to make up for the movement of the Bren.
 
@SDC: I agree with you. Uzi isn't all that bad, but you still can feel the movement of the bolt pretty good. More of a problem is the delay between pulling the trigger and ignition, it takes a while to get used to it.

Trigger pull isn't that bad though. Same goes for the Sterling.

SMG with a closed bolt (FAMAE, MP5 and the like) are just way more comfortable to shoot.
 
Keep in mind with pistol caliber SMG's the bolt travel is not that long as well - one the UZI it is over the balance point as well.

The longer the travel of the bolt the more the weight shift and cause a greater loss in accuracy
 
Also, as stated, most weapons that fire from the Open Bolt are mid to heavy MGs, they are used to cover or engage 'area targets' vs the more accurate fire required for 'point targets'.
 
The only weapons that I've fired from the open bolt would be the C9 and the C6 and because they are machineguns intended to cover an area with fire, any accuracy lost is negligable and inconsequential (even just with a bipod
Click to expand...
Excuse me the I thought the C6/C9 weapons systemes fired from a Closed bolt position :? . I have fired a Browning 1919 BAR in FA it uses a open bolt it was able to get a good group at 100m if using good trigger control on RnR it opened up quite a bit
 
Nope; both the C9/Minimi/M249 and the C6/FN MAG/M240 fire from the open bolt position, to allow more chance of cooling the bore when not actually firing. They don't have a fixed firing-pin, the way most open-bolt SMGs do, but when you flip the top-cover up and lay a belt in the feed way, the bolt will stay back (held by the sear) until you pull the trigger. Internally, the C6 works like a belt-fed Bren, where the hammer/op-rod cams the bolt into the locked position before it actually fires the chambered round, while the C9 is closer to the AR-15/M16, with a rotating bolt-head.
 
The C6 and C9 both fire from an open bolt, this prevents cook-offs.
On the C9, when the trigger is pressed, the piston assy moves forward under pressure of the return spring, carrying the bolt and bolt carrier assy forward. the feed horn on the bolt strips the cartridge from the link and forces the round into the chamber. The bolt and carrier continue forward until the bolt lugs contact the rear face of the breech, stopping forward motion of the bolt. The bolt carrier assy continues forward, and the cam slot on the carrier contacts the cam lug on the bolt, rotating and locking the bolt lugs in the locking lug recesses. Only after the lugs are fully locked, does the forward motion of the carrier bring the firing pin forword to strike the primer of the chambered cartridge.
This concludes this part of the theory of operation for the C9A1 LMG. Smoke break. Be back in class in 10 minutes. :)
Pat
 
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