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Posted: 1/21/2012 8:16:40 PM EDT
| What is the purpose of the spring on the bolt? I have seen other piston uppers' bolt carriers that the bolt did not have the spring on such as LMT. Do I have to keep it? What purpose does it serve? |
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Answered your post in the DI section
On a DI the gas pressure slightly moves the bolt forward, releasing pressure on the locking lugs as the bolt starts to unlock. On a piston system there is no gas pressure to do this, so the little spring is supposed to gently push the bolt forward so the there isnt such a jarring force applied to the locking lugs. My CMMG has one too. Oh edit for your second question, leave it in there it is serving a purpose. enjoy not cleaning your new AR 
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What is the purpose of the spring on the bolt? I have seen other piston uppers' bolt carriers that the bolt did not have the spring on such as LMT. Do I have to keep it? What purpose does it serve? Useless gimmick. Let me explain why: On DI you got the following: http://img263.imageshack.us/img263/9726/85878231.jpg Where Fb: Backward Force applied Fg: Gas Expansion Force When the ammo ignites, it apply force in every direction inside the case, the barrel contain most of this forces, the bullet get push forward by the forward force, and the bolt locked in the barrel extension contains the backward force. Then when the gas is redirected into the BCG Fg is applied again in every direction (as the gas expand inside), the bcg can only go rearward as the bolt cannot go any further, Fg is also applied forward pushing the bolt trying to counteract Fb. On Gas Piston you got the following: http://img39.imageshack.us/img39/5557/36787120.jpg (Yeah I know it's DI diagram, but try to think that the gas tube is the op rod and the gas key is the strike plate, and there is a bolt spring there) Where: Fb: Backward Force applied Fop: Op Rod Force applied Fs: Spring Force, trying to return to it's initial state. When the ammo ignites, it apply force in every direction inside the case, the barrel contain most of this forces, the bullet get push forward by the forward force, and the bolt locked in the barrel extension contains the backward force. Then when the gas expands inside the piston, it push the op rod rearward, which in time, hit the strike plate, making the BCG go rearward, The Bolt Spring is there, pushing in both direction, but it's small accumulated force, cannot counteract Fb and only push the BCG rear from the bolt. The thing is Fb >>>>>>>>>>>>> Fs, you can really say that Fs is insignificant compared to Fb, almost near 0; as opposed on DI where Fg pushing the bolt is a considerable percentage of Fb. So, if you are trying to reduce the force applied on the locking lugs hence reducing the wear on the locking lugs, you are just wasting your time and money, as the locking lugs will see no different force applied with the Bolt Spring added. That's why I said It's a "Useless gimmick" |
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What this seemingly innocuous little spring does is to retard the disconnect time long enough to reduce backpressure in the system. It also helps your bolt disengage from the barrel extension cleanly instead of being ripped out by the sudden rearward travel of the BCG as it’s pushed by the rod assembly. In essence the spring mimics the more smoothly running gas systems of old without all the fouling that gets shot back into the upper. The one-piece BCG system also eliminates cam pin drag. The spring makes the mating surfaces between the carrier, bolt, and cam pin float smoothly past each other. The bolt is so well balanced with the spring inserted that if you take it and place it bolt down on a tabletop, it’ll actually support the entire weight of the carrier above it but will flex downward at the slightest push. It also makes inserting it into your upper an easier task all around. No longer do you have to swing the BCG out to get the bolt to lock in an extended position; it’s always that way from the positive pressure of the spring.
Source: http://www.tactical-life.com/online/guns-and-weapons/adams-arms-pdw-556mm/ |
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What is the purpose of the spring on the bolt? I have seen other piston uppers' bolt carriers that the bolt did not have the spring on such as LMT. Do I have to keep it? What purpose does it serve? Useless gimmick. That's why I said It's a "Useless gimmick" Sorry but you are wrong here. The POF system uses a specialized roller pin cam bolt to accomplish the same thing as the spring. The Spring provides enough counter pressure on the bolt to prevent it from moving to rear while the bolt carrier is moving the first few critical mm's to the rear. As the bolt carrier starts to move back, the bolt and cam pin have enough friction that they stay locked in place until the cam pin strikes something on the interior of the upper receiver, which forces the cam pin to follow the cam path in the carrier. The roller pin that POF offers lowers the friction in this critical area but the spring offers enough energy to counteract the friction completely. Wes |
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Sorry but you are wrong here. The POF system uses a specialized roller pin cam bolt to accomplish the same thing as the spring. The Spring provides enough counter pressure on the bolt to prevent it from moving to rear while the bolt carrier is moving the first few critical mm's to the rear. As the bolt carrier starts to move back, the bolt and cam pin have enough friction that they stay locked in place until the cam pin strikes something on the interior of the upper receiver, which forces the cam pin to follow the cam path in the carrier. The roller pin that POF offers lowers the friction in this critical area but the spring offers enough energy to counteract the friction completely. Wes The POF Roller Cam Pin, is not in question, on the contrary, the Roller Cam Pin is something really useful you can see the link below why: http://www.youtube.com/watch?v=6JmIQXkoog8 However the BOLT Spring is just gimmick, with the bolt spring, you are adding a new constant when it is not needed, on DI that force is present just on the extraction, but the spring is THERE ALL THE TIME, not just for the extraction, it's also in the feeding and locking, exactly where you don't need any opposite force been applied. |
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Carnage, that was a very well thought out reply, with interesting diagrams. However, I believe you are mistaken.
In a DI system, as the gas builds in the BCG behind the bolt, it pushes the bolt forward (keeping it in place) as the BCG begins moving aft, until the cam can rotate and unlock the bolt. In a piston system, the BCG moves back earlier and more abruptly from the transfer from the op rod, and since is is a kinetic blow to the strike face, there is no countering pressure to delay the bolt moving to the rear (or trying to), so there is a greater pressure against the locking lugs when the cam unlocks the bolt. The spring does not provide a large force in comparison with the pressures created during firing, but it does not have to. It is not directly countering those forces. It is simply there to delay the bolt for a fraction of time until the BCG has moved far enough back to unlock the bolt. ETA: remember, by the time the BCG has started moving, the detonation force of the round is gone. Also, I think a better 'marketing gimmick' would be to state that "MY piston system doesn't need any silly bolt spring to oprate! Less parts; Less to go wrong!" if anything, the adoption of the bolt spring by so many different piston kit makers is more of a clue as to how effective it is. Posted Via AR15.Com Mobile |
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Carnage, that was a very well thought out reply, with interesting diagrams. However, I believe you are mistaken. In a DI system, as the gas builds in the BCG behind the bolt, it pushes the bolt forward (keeping it in place) as the BCG begins moving aft, until the cam can rotate and unlock the bolt. In a piston system, the BCG moves back earlier and more abruptly from the transfer from the op rod, and since is is a kinetic blow to the strike face, there is no countering pressure to delay the bolt moving to the rear (or trying to), so there is a greater pressure against the locking lugs when the cam unlocks the bolt. The spring does not provide a large force in comparison with the pressures created during firing, but it does not have to. It is not directly countering those forces. It is simply there to delay the bolt for a fraction of time until the BCG has moved far enough back to unlock the bolt. ETA: remember, by the time the BCG has started moving, the detonation force of the round is gone. Also, I think a better 'marketing gimmick' would be to state that "MY piston system doesn't need any silly bolt spring to oprate! Less parts; Less to go wrong!" if anything, the adoption of the bolt spring by so many different piston kit makers is more of a clue as to how effective it is. Imortal: You are right, maybe I'm a bit biased as I assume that the POF roller cam pin is a must for piston operated gun, as it smoothen the action and makes to bolt not to follow the bolt carrier while is moving the first few critical millimeters to the rear, and In that case the bolt spring is useless, however installing a bolt spring as is may induce other problems, as you are adding a new constant to the feeding and the locking. Remember that at the last few millimeters of the feeding/locking the bolt carrier has to overcome the power of both the extractor and ejector spring and now of the new bolt spring, or you will get a failure to lock, that could happen with either weak ammo, or weak/wear buffer spring. If you add a stronger buffer spring to overcome this, you could also induce the weapon to short-stroke and then everything start to turn into a nightmare. With all this risk induced by a simple spring, I recommend not to use a bolt spring (unless the weapons was designed to) use the roller cam pin, and you will get better results. Sorry again if I'm a bit biased, but in my country the most available 5.56 ammo is the dirtiest, cheapest, weakest FAMAE's stuff, it works great on Galils but a nightmare on ARs |
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Carnage, you raise a good point with the lockup perhaps being a problem. Not one I have experienced, but I will admit to the potential. My AR will lock up just fine, but some very well used rifles may have weaker buffer springs and have issues. It is. LT a problem I expect to have, but others may have other considerations in mind.
I still maintain, however, that the benifit of having it owtweighs the hazards of having it or the effects of not having it. Posted Via AR15.Com Mobile |
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Someone needs to manufacture those springs. Adams Arms wants $20.00 for them... $5.00 for the spring and $15.00 to ship em. What a rip off..  It looks to be a fairly common spring, look around and you will probably find it but I bet you will have to buy in quantity. Spring for AA Bolt: 4.75 coils 0.022" wire dia. from calipers. 0.302"O.D. x 0.63"L from calipers 0.105" Solid length from calipers 4 to 6 lb/in spring rate (est.) Close to 5/16" x 5/8" x 0.022" |
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Someone needs to manufacture those springs. Adams Arms wants $20.00 for them... $5.00 for the spring and $15.00 to ship em. What a rip off.. CMMG's springs are a little bit cheaper and they are cheaper on the shipping. http://cmmginc.secure-mall.com/item/Piston-Carrier-Bolt-Spring-1468 They also carry a wider range of products you might be interested in buying as well so you could combine ship. Wes |
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Someone needs to manufacture those springs. Adams Arms wants $20.00 for them... $5.00 for the spring and $15.00 to ship em. What a rip off.. Not trying to start anything, but why would you only buy one? Buy a dozen of them, then you don't have to worry about the $15 shipping for awhile. They aren't going to go bad from sitting. I keep a spare with the spare bolt in my MOE+, and the rest are in my spare parts bin. |
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Someone needs to manufacture those springs. Adams Arms wants $20.00 for them... $5.00 for the spring and $15.00 to ship em. What a rip off.. Not trying to start anything, but why would you only buy one? Buy a dozen of them, then you don't have to worry about the $15 shipping for awhile. They aren't going to go bad from sitting. I keep a spare with the spare bolt in my MOE+, and the rest are in my spare parts bin. I understand what your saying. That spring will last forever. Even if it broke you could run without it. It burns me up when retailers crank up there shipping charges. I guess they would call it "handling" charges.. CMMG beat them out by $2.00 dollars plus $1.00 cheaper. I guess I could buy a few and sell them on the EE here for half price shipped and off set the cost a little bit... |
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Someone needs to manufacture those springs. Adams Arms wants $20.00 for them... $5.00 for the spring and $15.00 to ship em. What a rip off.. CMMG's springs are a little bit cheaper and they are cheaper on the shipping. http://cmmginc.secure-mall.com/item/Piston-Carrier-Bolt-Spring-1468 They also carry a wider range of products you might be interested in buying as well so you could combine ship. Wes Thanks for the link. I'll use it.. 
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Someone needs to manufacture those springs. Adams Arms wants $20.00 for them... $5.00 for the spring and $15.00 to ship em. What a rip off.. CMMG's springs are a little bit cheaper and they are cheaper on the shipping. http://cmmginc.secure-mall.com/item/Piston-Carrier-Bolt-Spring-1468 They also carry a wider range of products you might be interested in buying as well so you could combine ship. Wes Thanks for the link. I'll use it..
If you take a look at this thread: http://www.ar15.com/forums/t_2_145/214281_Shipping_on_small_parts___.html You'll see CMMG is willing to ship for less if you call them. Wes |
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