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Posted: 10/15/2006 2:20:56 PM EDT
| I can't seem to find detailed info on how roller locking is different than roller delayed except that the rollers on the mg3 lock into the barrel extension. I understand roller delayed, but how does roller locking work? Anyone have any good information about the MG3 locking system? |
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They work pretty much the same. The difference between the MG3 (which is the MG42 in 7.62NATO) and the G3 are that the MG3 stays locked during the begining of travel. The barrel and extension recoil with the bolt and the locking lugs stay out and locked during the peak pressure. Once the assembly travels far enough back, the rollers cam in and the rest is pretty much like the HK. All any "locking" systems do anyway is actually "delay". Otherwise the gun would never work because it would stay "locked". So even a locking system like the Browning 1911 simply delays unlocking until the slide moves far enough back. Some people will argue semantics, but they are really all "delays". I suppose the MG42/1/3, etc. are considered "locked" because they stay locked during actual recoil and initial movement of the bolt. The HK simply gets pushed on hard enough to eventually push the rollers back in and allow the bolt to move. |
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Roller locking is a method of locking the bolt to the barrel/extension, and relies on recoil or a gas piston to unlock and cycle the action. Similar to rotating or tipping bolts, or the dropping/camming barrels in browning type autopistols. Roller delay is a method of delaying the opening of the bolt via a mechanical disadvantage. The force of the cartridge case pressing against the boltface immediatley after firing opens and cycles the action. Similar to "straight" blowback except instead of inertia delaying the cycle, it is the mechanical disadvantage. |
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I don't think they're the same. Roller locked, like in an MG-42 machine gun or CZ-52 pistol mean it's locked. The breahface does not move relative to the chamber until a certain point. On both guns, the breach and barrel assembly moves rearward to a pre-determined point and which point the rollers are retracted and the two are allowed to seperate, allowing the breach to move away from the barrel, extracting and ejecting the case. On a roller delayed gun, the barrel is stationary and the the breach face is allowed to begin movement as soon the powder creates pressure. It takes a massive amount of force to unlock completely, but it's still a delayed basic blowback. It's never "100% locked" like a roller locked gun is. |
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How are they the same? On a roller locked gun the bolt face is locked to the chamber and does not move reletive to the chamber until the locked bolt/barrel assembly recoils together to a certain point in the gun's frame or receiver. Again, think of an MG-42 or a CZ-52. In a roller delayed gun, the bolt is never really locked. It's simply at an enormous mechanical disadvantage, as the above poster stated. The barrel is rigidly mounted to the gun's receiver. These are HKs and Cetmes. |
Not sure about this last statement, I read that the H&K rollers actually "bind" up due to the initial high back pressure and only when the pressure dies down to a "safe" level do they unlock/disengage and allow the bolt to move back. Kind of works like Chinese hand cuffs the harder you pull the tighter it gets. This is why the fluted chamber is necessary it creates channels for the gasses to float or un-stick the brass case which aids in extraction. Just what I’ve read |
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Ross' description is the most accurate. While the two systems are not technically identical, they are still siblings. The architecture is the same: a roller is used as the motion transfer medium between opposing, angular surfaces. The rate of this transfer is controlled by the rate of the angles. In the MG3 / MG42 the barrel extension and bolt head are "held" together via the force of the recoil spring - after firing the barrel moves rearward under recoil until the surfaces of the bolt's two locking rollers contact the unlock ramps in the receiver. In the G3 / MP5 / CETME Ameli the barrel extension is replaced by the trunnion, which is fixed in the receiver - the primary difference is that the force is transferred (via the rollers) directly from the bolt head to the trunnion to the locking piece - there is no primary delay due to barrel movement. In either example, the bolt carrier will begin to accelerate rearward faster than the bolt head, due to the principle of operation. This is also what provides for a margin of safety between primary ignition and unlocking. Complete details are covered here: www.hkpro.com/technical.htm To put it another way: the angles of the locking piece (on the bolt carrier) push the rollers out of the bolt head to lock it into the trunnion (G3) or barrel extension (MG42). The angles of the trunnion or barrel extension push the rollers back into the bolt head to unlock the carrier. The carrier will move rearward faster than the bolt head (the delay in roller-delayed), and during this event the chamber pressure drops to a level safe enough for extraction to occur. Hope this helps, Clint |
Now I understand it.
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