Quoted:
I like to increase the reliability of carbine or midlenth ARs by using:

1) A big, big gas port

This provides more BCG/buffer energy that can be used to extract, or with a stronger spring, feed.

2) A heavy, heavy buffer

This keeps the initial BCG/buffer velocity the same, so extraction timing is not changed significantly- some high school phyics can help in understanding my design - remember that kinetic energy is m v**2 / 2

3) Light loads

These ease extraction, increase barrel life, and reduce gas port erosion.



Will higher pressures inside the BCG expansion chamber lead to parts breakage? Maybe, to some extent - but see 2). BCG velocity is not increasing, so extraction is not more "violent" (to use an imoprecise term)

Could the BCG/buffer slam against the end of the receiver extension? Sure, but this is what I want - lots of excess energy.

Comments and criticism are welcome.

Quoted:

Not necessarily the best design... (a lot of what follows is going to be "in perspective.." at points we're kind splitting hairs/beating a dead horse) I mean you'd want to try to find "harmony" for lack of a better term.  I guess the question would just be, why?  Larger gas ports and heavier springs are going to cause you to have some serious heat transfer from gasses to metal surfaces.  Because the consistencies of the metal and it's components are made out of, you WILL have uneven expansion/contraction/hotspots/stress points to a further extent that is necessary.  This will augment your accuracy as the temp of the metal changes at different rates.  Not to mention your design will bear pretty harshly on the gas system.  Using these components to "increase reliability" can be arguable.  Maybe in the short term, but you will suffer some losses in accuracy and wear and tear.  lets go point by point:
1) A big, big gas port




*** to reiterate, you're allowing more gas into your system here, thereby increasing all of the following: gas velocity, thermal transfer to the weapon, carbon fouling of all major components, allowing DRASTICALLY more gas into the actual receiver of the weapon as the bolt carrier rides back.  
2) A heavy, heavy buffer




*** here you're just requiring more gas necessary to cycle/move the BCG.  The "violence" as you put it, of the bolt and carrier group moving may not change, but the energy needed to move it has increased.  That energy comes with drastically more heat from the required gasses.  Again, increased heat/fouling, etc.  Higher chamber pressures will result (not good for your jammie)
3) Light loads




*** there is no problem with shooting light loads.  You just need to take into account the rifling of your barrel.  Light loads are not a variable that pertain to your "design."
The overall goal when building a carbine for a specific purpose is to ease stresses (both mechanical and thermal) on all components of the gun.  While what you came up with may not necessarily add excessive mechanical wear (however, with a heavier spring and buffer it DOES stress the BCG from riding forward more violently.  You will see more wear on your feed ramps, the bolt it self, and your chamber.  You want to use the lightest buffer you can, the least gas you can, and a spring that manages your recoil appropriately.  "overgassing" for reliability probably isnt the most practical approach.

Quoted:

OP -



1) Try it and see what happens...



2) I'm a mech eng. but I'm going to take a non-scientific viewpoint.

The AR is a mature platform. Manufactures are motivate to produce a product that is reliable over the widest range of possible conditions and they have the resources to experiment with a lot of different parameters in a quest for a ‘better’ AR. They may have already tried the ideas you are suggesting and rejected them.



Do you see any major manufactures (DD, LMT, etc) taking this approach?

Quoted:

I have tried it and it works beautifully.

I think that the manufacturers want to stick close to mil spec. Plus they may not be strong on Phys I topics like simple harmonic motion.

Range guns don't get much foreign debris, and mil designers have other concerns, as I said.

As far as the "overthinking" phrase a few posts back, my method will work under conditions where others fail. That's the good kind of thinking, isn't it?

Of course the statndard reliability advice like using good mags is true, but why not have an energy reserve too?

Quoted:

There are plenty of guys who have had no problems with their rifles over seas during combat, in talking to them all they did was keep their rifles lubed. I have family and friends in military who saw combat often over there and none had issues with their rifles. They even swear by their rifles.

ETA: in 99% of cases the military should not be firing their rifles in full auto, thats generally considered a no-no. Thats what happened at Wanat, to much spray and pray auto and not enough accurate aimed semi auto firing.

Quoted:



What makes you believe and overgassed AR will work when others fail? Last time i checked the AR is working in the worst environments possible.

Quoted:



Are you saying that foreign debris hasn't caused stoppages?

Consider the case where the bolt just barely fails to pick up the next round due to foreign debris friction (maybe combined with other things) during the first part of the cycle. A 15% larger BCG energy will move the bolt back further, the round will be picked up, and there will be no stoppage.

I'm not disrespecting the AR, it's my rifle. But if I can enhance reliability and will accept the trade offs (which the mil and big manufacturers may not be willing to accept), the rifle is even better.

Quoted:
But your not enhancing reliability.
If anythig you are puttig extra strain on the parts in the rifle shortening their life span.
A lubricated M4 will run even covered in moon dust, im sure wolf can attest to this

Quoted:


   Like I said, I'm willing to accept the extra fouling and heat transfer, and higher BCG chamber pressure, but my idea shouldn't put extra tension impact on the bolt, since intial BCG velocity doesn't change. The stronger spring may increase the impact at the end of the cycle, but this means there is an energy reserve for feeding. This seems like a good trade off.

If a lubricated M4 will run even covered in moon dust, they're sure wasting a lot of time cleaning unfired guns in Afghanistan. The dust on the outside doesn't concern me, it's the stuff that works its way into everything over time. Note which state I'm from.

Quoted:



You need to view this thread, thats about as big of debris as youll get in the AR and his ran fine as does everyone elses.





Why i like my lmt

Quoted:


   Thanks for the link - great thread. Food for thought.

This guy says he didn't clean his rifle, but he seems to keep it extremely well lubed. Again, I'd prefer to be less dependent on this.
 

Quoted:





The AR require lube, thats just how it is.

Quoted:


 

    My setup doesn't, for quite a while anyway - that's one of the points.

Sure, enough fouling and enough dust will stop one of my carbines. But if there is a shortage of time and resources, mine will run dustier and dryer for longer than the usual setup. This kind of robustness seems important in a weapon.

Again, thanks for the lube recipe.
 

Quoted:


Keep in mind that most of the ARs on the market are already overgassed as it is.

My LMT carbines all use a .071 port and are extremely reliable. I do match the buffer to the loads, a carbine buffer for low powered .223wolf and whatnot and a H-H2 for larger (75,77)5.56 loads.

Quoted:





Maybe i just dont understand your mind set here.



Unless your going to be pouring in pounds of stand into the receiver and dont plan to clean for 10,000 rounds what your doing is dumb.



If you clean your rifle every 300-500 rounds you may be able toget by bone dry, still seems stupid to me. I mean we will never have a shortage of lubricants. Even if the world ended tomorrow there is enough quarts of motor oil on shelves that you can easily steal a few and have enough lube for your life time.



I mean 4 drop of lube will get you by for 500-1000 rounds, i just dont understand what your trying to accomplish

Quoted:



Thanks for the data.





I've been using a .076 gas port with a 14.5 barrel carbine, an H3 buffer and the red Sprinco spring. I'm going to go with at least a .076 port on a 16" next.





As I said, most of my shooting is at .223 pressure levels. This setup gives me several hundred trouble free rounds in the desert with no cleaning and no lube. I do use a Ni-Bor BCG.


 

Quoted:


  I see your point, but the guy in the thread you linked used a lot more than 4 drops. You can see it thick on everything. And there's not always time and energy and lube to take care of things.

Camping in the desert, everything gets dusty, including the tip of your lube vial, patches (the wind came up when you left the pouch open), the shirtail you use when the patches run out, etc.

I'm trying to make the weapon a little more robust in this area.

I really like the PMAG mag covers, because fine dust on the ammo gets into the chamber, and then you'll need all of the energy reserve you can get.


 

Quoted:







I failed to mention that these are 10.5" barrels with a carbine length gas system. Big difference there. .076 on a 14.5 is HUGE. Colt specs a .063 for 14.5 and 16" which I find overgassed. Colt specs a .093 on their 10.3 and as I posted my LMTs do great at .071, never had a single failure on 3 different firearms.

 

Quoted:





Its an amazement our guys in combat days on end can do it. You have been here since 2006 yet say stuff like energy reserve?



My mind is blown.

Quoted:


  Uh, "energy reserve " is a fairly common mechanical engineering phrase. This is the discipline that came up with the AR design, right?

Some times our guys do it and sometimes they don't, especially if they have been out for a few nights. Or so I've read.


 

Quoted:

I like to increase the reliability of carbine or midlenth ARs by using:

1) A big, big gas port

This provides more BCG/buffer energy that can be used to extract, or with a stronger spring, feed.

2) A heavy, heavy buffer

This keeps the initial BCG/buffer velocity the same, so extraction timing is not changed significantly- some high school physics can help in understanding my design - remember that kinetic energy is m v**2 / 2

3) Light loads

These ease extraction, increase barrel life, and reduce gas port erosion.


Will higher pressures inside the BCG expansion chamber lead to parts breakage? Maybe, to some extent - but see 2). BCG velocity is not increasing, so extraction is not more "violent" (to use an imprecise term)

Could the BCG/buffer slam against the end of the receiver extension? Sure, but this is what I want - lots of excess energy.

Comments and criticism are welcome.  

Quoted:


Maybe read this thread  ––>  http://www.ar15.com/forums/t_2_138/196990_Filthy_14_is_now_over_40_000_rounds.html



Pat Rogers has been using a undergassed middy with very little cleaning for quite some time, and I believe he only allows 5.56 loads to be used.

I believe you are on the wrong path, but it is yours to take and do with what you want.

I see other engineers create a solution that creates a worse problem than the origional problem.

Go for it if you want, it seems to me you are taking energy away from the projectile and projecting this on the carrier, kinda defeating the need for a reliable weapon.

Energy projected on target would allow time to lube.

Different strokes

Quoted:
For what it's worth the only time I've had an AR jam was an M16A2 that had a couple magazines full of mud/silt covered ammo shot through it. My D.I. had me clearing double feeds and forcing rounds into the chamber using the forward assist until I ran out of ammo

Quoted:


was that during active duty? its a good example of how magazines lead to 90% of all stoppages in the system

Quoted:

me thinks op doesn't know how the AR system really works.



you realize that if your system runs at the normal 700rpm then the bolt carrier is moving at the same average extracting velocity as everyone else. there is no "extra energy reserve."



the gas system is self regulating after a point. once the carrier key moves back the half inch or so, gas is no longer supplied. IF your slowing down the cyclic rate to a normal 700rpm with a heavy spring and heavy buffer the only think your doing is increasing bcg pressure. you are getting no "energy reserve", it doesn't work like that.

Quoted:


Again, point by point,


The heavier buffer means more kinetic energy at the same cyclic rate, and thus an energy reserve. See point 2). That's how kinetic energy works.

The bullet is long gone by the time the carrier moves back 1/2 inch. Try multiplying a typical BCG initial velocity (15 feet/sec) by the dwell time ( a fraction of a millsecond) to see how far back the BCG moves.

A heavy spring doesn't slow down the cyclic rate, it speeds it up, unless the reciprocating mass increases proportionally, in which case the cyclic rate will stay about the same.


You say I don't understand the system?

Quoted:

I dont think you do undertand the system.



A heavier buffer and spring reduce cyclic rate, ...



A heavier buffer and a heavier spring can cancel each other, so that cyclic rate doesn't increase. In engineering terms, the frequency of a simple harmonic oscillator is proportional to the square root of the spring constant divided by the mass. If both increase proportionally, the frequency is unchanged. Our system is not quite a simple harmonic oscillator, but you get the idea.



In layman's terms, the heavier buffer slows the cycle down, the stronger spring speeds the cycle up.









Increasing the gas port only makes the rifle unlock more violently. Not with a heavier buffer. The more massive buffer keeps the BCG initial velocity the same, even though there's more gas. This is why I said in 2) in the original post that initial BCG velocity won't chase, so extraction will not be more violent.





Now if you offset that with a H3 buffer you will get the same results you would get with a proper ported rifle using a H buffer, but now you have no options of changing when and how your rifle unlocks



The results won't be the same because I now have a more massive BCG/buffer which gives more energy to overcome friction, and to transfer more energy to the spring for more robust feedibng - the point. And I do have the option to change the unlock time, because there are much heavier buffers than H3 out there.

Quoted:
Why not just run a VLTOR A5 system with the heaviest buffer you can with a standard gas port?

This will get the results you want without dicking up your rifles gas port.

Your whole logic behind this makes no sense. You want the ability to power through crud when chamberig a round? Well you can do this with the A5(which has been found to be more reliable than the A2 Rifle system according to Marines)

Quoted:

Why not just run a VLTOR A5 system with the heaviest buffer you can with a standard gas port?



This will get the results you want without dicking up your rifles gas port.



Your whole logic behind this makes no sense.I've demonstrated problems with all of your objections, and my logic doesn't make sense? You want the ability to power through crud when chamberig a round? Well you can do this with the A5(which has been found to be more reliable than the A2 Rifle system according to Marines) The A5 on an overgassed system (the VLTOR page says that piston systems are usually overgassed) is just what I am doing, but with the DI system.

Quoted:

Quoted:

There are tons of thread here about over gassed rifles. What you are trying to do with the heavier buffer and spring are effort folks do to try and FIX ie. bring things back in to equilibrium when they happened to have a rifle that is defective/over gassed.



In my experience with an over gassed rifle:



Over sized port + standard buffer and spring = beat up buffer, substantially reduced buffer spring life and distracting/higher recoil impulse.



Over port + heavy buffer = substantially reduced buffer spring life and distracting/higher recoil impulse Over sized port + heavy buffer + heavy buffer spring = Back to equilibrium if your lucky, if not see "distracting/higher recoil impulse"



Back to equilibrium at a higher BCG/buffer energy, which is the point. Have you read the thread? And if there is a significant reduction in spring life (which I doubt there is with Cr-Si springs), it's because the bolt is going back further. This is what I want.



You have a point about recoil, but the impulse won't be greater (conservation of momentum) , it may just be differently distributed due to the BCG hitting the end of the receiver extension. I'm not saying that this is a plus.







What you are doing is at the very least canceling out the over gassing = factory spec rifle. Creating it and then canceling it to increase BCG/buffer energy.







It sounds like you have the engineering concept. But you also need to introduce in to that concept "you can't get sumthin for nothin". See the previous posts about the trade-offs



Now, with a properly gassed in spec rifle, again in my experience:



Heavier buffer = Less recoil impulse and expectation of slight decrease in reliability with low powered ammo(decreased reliability is theoretical because I have not experienced it)



Standard buffer + heavier buffer spring = increased reliability with dirty and or damaged ammo and expectation of slight decrease in reliability with low powered ammo(decreased reliability is theoretical because I have not experienced it)



Heavy buffer + heavy spring = Reduced reliability with standard, in spec ammo.





Again in my experience: The fine dust/sand particles you are worried about attracting and or introducing with your lube make not a good God Damn to an in spec rifle. It just dont matter. Fine sand anywhere near the chamber will matter several God Damns. Fine sand other places may not matter to a lubed rifle, but that's not what I'm trying to optimize. And I never said that lube attracts sand, just that wind blows it. Again, see the previous posts.



No lube = rifle chokes EVENTUALLY, noticeable increased wear on cam pin and gas rings. Well, I'm not claiming my system will run forever, just be more robust under the circumstances I mention. And does lube stay on the gas rings? I would think that the temperature in the BCG chamber would be too high. I'd like to know more about this.





Different strokes for different folks, but I think you could go on EE and place a Want To Buy Over Gassed Rifle and you will get some great deals on rifles already modified with heavier springs and buffers. It's so easy to ream my gas port. Bigger, that is