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Posted: 8/6/2013 10:58:28 PM EDT
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Gentlemen,
I have a real world project To avoid COMPLETELY starting from scratch and just staring at an M16 until I can visualize the mech manipulation, let us start at what I do know or have been advised on to date. The piston/operating rod designed types leave the BCG and chamber cooler and cleaner. [b]Okay, but if it were the answer or solution LWRC would not have developed their own version of the open bolt M4/b] The stress on the pins of the lower receiver is quite significant and will destroy the normal alloy of the AR lower. The lower must be done in a stronger alloy, steel or reinforced areas around the steel. Colt attempted this decades ago and to know just why their own was not practical would not hurt either. So, what are the basics behind a good open bolt design? I know a couple of you here can bring me into the light. |
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The OB designs don't destroy the lower, but they can be tougher on it. Colt has two open bolt systems out there with stock aluminum lowers (Colt LMG and M231 FPW), and several other OB designs have been implemented (LWRC's, I guess? and the AR-57, that I know of).
The fact that the US Military didn't adopt any of the M16 open bolt designs other than the M231 FPW don't mean they were impractical in themselves, but that the solution they offered didn't fit any role better than an existing alternative, so there was no reason to change. OB is desirable in a sustained-fire-role machinegun, because OB won't cook off as easily, and the airflow through the chamber and barrel aid in cooling. OB is detrimental in that there is more moving mass between touching off the trigger, and the round being fired and exiting the bore. In an area-denial and fire-superiority weapon like a sustained-fire machinegun, pinpoint accuracy is not necessary, so the open bolt detriments are not large in comparison to their benefits for cooling and reducing cookoffs. Not to mention that support weapons are heavier, and tend to have mounts of some sort - at least a bipod - that minimize the detrimental effects of that moving mass. In an infantry rifle which is occasionally called upon for precise and accurate long-range engagement of targets, the detriments of an open bolt system are felt more keenly, the rifle is lighter and has less support/mounts to minimize those effects, and the sustained rate of fire doesn't need to be so great that an open bolt system is fundamentally safer and more useful in that role. The basics of a good open bolt design are that the bolt strips, chambers and fires the round in a single cycle. How that is achieved depends a LOT on the operating system, the cartridge, the construction of the firearm, etc. First define your role and your cartridge, and you can then work on the how to do an open bolt system for it, and from there decide if it's worthwhile to implement it. |
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To clarify
I am looking to TRY and have an open-bolt for full auto fire on an AR platform. I am really not wanting to debate why or if I even have business trying. Some of you can answer the basic questions on how to do this and I would appreciate hearing from you. Thank You |
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Quoted:
To clarify I am looking to TRY and have an open-bolt for full auto fire on an AR platform. I am really not wanting to debate why or if I even have business trying. Some of you can answer the basic questions on how to do this and I would appreciate hearing from you. Thank You Study the Colt LMG open bolt system and the M231FPW system, then. The LMG achieves open bolt operation by using the hammer to hold the carrier back until the trigger is pressed, at which point the regular M16 auto sear design is used to fire the cartridge when the bolt has closed. The FPW system links the trigger to an internal carrier stop, and has a weighted striker to fire the cartridge when the bolt has closed. |
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Quoted:
Study the Colt LMG open bolt system and the M231FPW system, then. The LMG achieves open bolt operation by using the hammer to hold the carrier back until the trigger is pressed, at which point the regular M16 auto sear design is used to fire the cartridge when the bolt has closed. The FPW system links the trigger to an internal carrier stop, and has a weighted striker to fire the cartridge when the bolt has closed. Quoted:
Quoted:
To clarify I am looking to TRY and have an open-bolt for full auto fire on an AR platform. I am really not wanting to debate why or if I even have business trying. Some of you can answer the basic questions on how to do this and I would appreciate hearing from you. Thank You Study the Colt LMG open bolt system and the M231FPW system, then. The LMG achieves open bolt operation by using the hammer to hold the carrier back until the trigger is pressed, at which point the regular M16 auto sear design is used to fire the cartridge when the bolt has closed. The FPW system links the trigger to an internal carrier stop, and has a weighted striker to fire the cartridge when the bolt has closed. Colt's patent for the open-bolt LMG design is Patent Number 4,433,610. It's available at patent search sites. If you check the images of the patent itself, there are many line drawings of how it works, and how it differs from closed-bolt designs. Colt received the patent on Feb. 28, 1984, and has been making and selling LMGs (and the current product-improved LSW version) for decades. It is standard issue in the Canadian military. There is also a wealth of good info about the LMG/LSW here: Mongo's M16A3 LMG/LSW Page When correctly built and configured (hydraulic buffer, green spring, etc.) and fired with milspec ammo, the Colt open-bolt system puts little or no additional stress on the alloy lower receiver. While I've never seen service-life numbers, I doubt it would be in general issue if that number were significantly lower than closed-bolt alternatives. FYI, several companies have, over the years, prototyped fire-control systems that are Safe/Closed-bolt Semi/Open-bolt Full Auto. They demo well, but AFAIK no one has done any production runs. HTH. |
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