To my knowledge, no one has yet posted a How-To on this topic.  Here it is for anyone interested. I figured it out. I tried it. I like it.

Many DONT.   Many are utterly convinced that dropping a lightweight carrier into your AR will make your weapon explode and lead to erectile dysfunction. I might get flamed for this, but, oh well. What's the fun of posting stuff that no one has strong opinions about?

If you thought you might like to tinker in this area, but weren't sure how to proceed, this might be for you.

So, without further adieu, in the following post I present my how-to treatment on building a light weight operating system.

Enjoy...or not.

Wordmahn

HOW LOW MASS OPERATING SYSTEMS (LMOS) WORK AND HOW TO MAKE ONE

I believe a properly built lightweight operating SYSTEM can be reliable over all reasonable ammo choices on a semi-auto only weapon. The results can be fantastic --Incredibly light shooting. Before the he-men say that 5.56 is not hard recoiling, let me say that it's NOT about recoil really; It's about getting rid of muzzle jump. This is done by reducing the mass of the reciprocating components slaming around inside the rifle, reducing the gas that drives them, and cleverly redirecting the gas jetting out of the muzzle so it works for you instead of against you.

Forget gaming. A guy who can put twice as many shots on target per unit time, has a significant advantage in a gunfight, especially up close.  It can be done.

It's not dead simple to do this right, but if you're a tinkerer, the following guide should get you there. First remember that the AR works as a SYSTEM.  Make a big change to one thing and you really should change some others. The good news is that the Stoner system is incredibly forgiving and will tolerate a lot. But if you want to minimize the impact on reliability and long term wear, treat it as a system.  

HERE IS THE HOW-TO BREAKDOWN:

Bolt Carrier -- The first and easiest component to change is the bolt carrier. Aluminum bolt carriers are the ultimate but they haven't built one yet that will hold up long term. Aluminum carriers are also more "finicky".  TOO light, perhaps. I went with a V7 Ti carrier. Ti carriers are the second lightest and much more durable than aluminum. A good, skeletonized steel carrier is also a good choice. They're stronger and, some are almost as light as Ti.

Gas Length -- The length of the gas system and where it taps into the barrel changes the timing, the amplitude, and shape of the gas pressure curve that unlocks the bolt and helps drive it rearward. Genearally speaking, a shorter gas system is harsher on the shooter and the hardware.  For best results a mid-length or rifle length gas system is reccomended. For barrel lengths under 18 inches a middy is best. My 14.5 is a middy.

Adjustable gas -- This should be mandatory, though some people successfully run slightly lighter carriers without them. Most ARs are already over-gassed. If you significantly lighten the moving parts without reducing the gas that drives them, you will probably OVER drive them.  You can buy adjustable gas TUBES, adjustable gas KEYS for your carrier, adjustable gas CARRIERS, and even an adjustable gas upper RECEIVER. The most common and best solution IMO is the adjustable GAS BLOCK. One of the best and most trusted names is SLR. I went with their lightweight Ti Sentry Premium.

Buffer tube -- It is well known that a rifle length buffer system with its longer spring is the softest and smoothest shooting. If you're doing an m4-ish build, this isn't so practical unless you like a fixed rifle stock. So most go with the standard carbine length buffer tube and spring. But wait! There's a compromise solution. The Vltor A5 buffer tube (AKA receiver extension) system was developed for the Marine Corps to give rifle-like smoothness and reliability for collapsible stock carbines. Its length is in between that of the standard rifle buffer tube and the standard carbine tube. It uses a rifle length spring and a proprietary buffer. The longer A5 provides extra smoothness and some reliability insurance against the faster, more finicky cycling of a lightweight operating system. I went with a Vltor A5 and highly recommend them.

Buffers weights --  For the very best results you can reduce the buffer weights and work with different springs. Some people completely strip out the weights inside their buffers and run them hollow. I don't recconend this. Buffer weights act like a deadblow hammer to reduce bolt bounce. Retaining some deadblow effect is probably wise. It's not as important in a semi-auto as a FA gun, but still best to have IMO. There's also polymer buffers with no deadblow weights in them. Fine for a purely fun gun. Not for me. I went with Vltor's lightest buffer, 3 oz IIRC.

Buffer springs -- The next to last piece of the hardware end of the puzzle is the lowly buffer spring. Here's where it becomes almost black magic with people proclaiming this or that spring to be the hot deal. They sell reduced power springs, extra power springs, and standard power springs. Some people even clip coils. JP Enterprises sells a unique "Silent Captured Spring" setup with special springs and weights, all tunable for weight and spring rates. They say it makes your AR cycle extremely quiet and smooth. Confused yet? Too little stiffness in your buffer spring and your bufffer will slam against the end of your buffer tube, and you might not have enough return force to strip the next round and chamber it. Too stiff a spring might cause short-stroking or excessive bolt bounce, or make your carrier return stroke so fast that it fails to strip the next round from the mag. I found this part of the puzzle to be the trickiest, but there IS an easy solution, so don't despair.  The easy solution is the more-or-less, one-size-fits-all, CS flat wire springs. They smooth up the action, have better compression characteristics, and last forever. I went with the very popular Tubbs.  It's working like a champ for me. Maybe I'll get brave someday and try clipping some coils.

Muzzle Device -- I probably should have listed this as the first item. Everyone knows that a muzzle device can dramatically reduce recoil and muzzle jump. In fact, this part can probably have as much effect as all the rest put together. For fun guns and competition rigs there's tons of good "comps." The most effective ones are obnoxiously loud, flashy, "blasty". They redirect the expanding gasses exiting the muzzle to push the gun away from you and partially cancel recoil,  which can dramatically reduce muzzle jump. Recoil mitigation by as much as almost 80% according to TTAG's superb testing (Which should be required reading. Google it.).  For guns that might be used for social purposes, flash suppression is needed. But few, pure, flash suppressors provide any recoil compensation. This is where the "combo" devices come in -- muzzle devices that are SUPPOSED to provide BOTH flash suppression AND compensation. Despite their bold claims, most combo devices fail badly at one or both functions. Again, see TTAG to get the scoop. One of the few combo devices that does a fair job at both flash suppression AND recoil reduction is the Precision Armament AFAB. It was my choice hands down.

Setting the Gas Block -- This last critical step must be mentioned. Some gamers dial their gas block down to the razor's edge with JUST enough gas to run the action on their chosen load.  This gives them the very smoothest shooting and the lowest muzzle jump for the fastest split times.  This is a bad idea for anything you might use in a defensive role.

A big key to more robust reliability with a LMOS is to set your adjustable gas as follows:

1, Find the wimpiest .223 load you can ever imagine using and load one round in the mag.
2. Chamber and fire it while intentionally  *limpwristing* the gun one-handed (To create a relatively worst case for cycling.).
3. If the bolt locks back as it should, turn the gas down one notch and repeat.
4. When the bolt finally fails to lock back, turn the gas UP two notches. You should be good. Go three if you're really concerned, but it won't be as soft.
5. Now run a full mag of the wimpy stuff *limpwristed* just to be sure everything works.
6. Run hot, 5.56 mil pressure 77 grain loads and check for function.
7. Run your chosen load and check for function.
8. Train with it, and get it hot and dirty. If all is well, you should be GTG.

* Note:  One important variable is temperature. If you shoot in an area where temperatures plummet, do the wimpy ammo test on the coldest possible day with the weapon cold. Cold ammo doesn't create as much energy to cycle the action and cold lube creates more drag.  Leave the weapon AND the ammo out in the cold for hours before you run the procedure.

** If you change any component in the operating system, you should repeat the gas setting process above. I once tried a different muzzle device and discovered that the change in back pressure caused weak loads to not lock the bolt. Remember, it's a system.

CONCLUSION

It's a lot to do but the reward is an almost unbelievably soft and fast shooting weapon. By avoiding the extremes and using good parts, I have a system that  I feel I could trust with my life.  It's been 100% for me so far. There's no doubt that a standard, over-gassed, heavy operating system AR will be more reliable. So would a bolt action. It's about how far you're willing to go to have a faster, smoother, higher-volume weapon. The very highest reliability or a higher effective rate of fire. It's your choice.

But sometimes quantity really does have a quality all its own.

Wordmahn

Thanks!!

Oops. I see that I forgot to mention the muzzle device. I'll edit that bit in,

Wordmahn - like PursuitSS said, well done.  Good rationale for your component selections.  Your tuning is oriented to reliability rather than getting the flatest shooter, but good regimen.  Thanks for taking the time to write it up.  It will help as a reference for newbies to LW ARs.

Thanks a bunch, Linc.

I provided my choices as an example, not to imply that they were necessarily the best for everyone. But you probably know that. And I was intentionally conservative in everything as this is for my SHTF gun, rather than a game or play gun. Many would say only go milspec heavy on any defensive piece. I hear it over and over. I think it's safe to go LMOS if one is conservative, uses quality components, and does not tune to the razor's edge.  For a game gun I wouldn't hesitate to push the envelope further.

I hope they will keep it up as a reference for newbies. I spent many, many hours reading and experimenting to figure it all out. I've got some boxes of spare parts to prove it. Ha. If anyone knows better ways or better stuff, I hope they'll chime in.  

Thanks again, Brother.

ONE MORE THING --

Here's another point about obtaining super flat (least muzzle jump), fast shooting. I didn't include it in my how-to because this part is mostly about shooting technique rather than equipment. It's something that most gamers and top tier operators know about, but I did not find out about till later.  Here's how I discovered it:

After I completed my lightweight stick with the low mass operating system, I found that it indeed had less muzzle movement and could shoot faster strings. But I wasn't getting the .22-long-rifle-like experience that I kept hearing about from others. This frustrated me. I had done and tried almost EVERYTHING to get there. I chalked it up to the fact that my stick was really light and would therefore probably never be able to get me to the smoothest shooting. I was wrong.

One day as I was shooting with my son and my nephew, a thought popped into my head that I'd read somewhere: Someone said that for less muzzle jump, shift the butt of the rifle down and over toward the center of the chest. More on your pec muscle. So, on an impulse, I did that and fired. Result: NO movement of the gun. None!  I pulled up the rifle and looked at it in wide-eyed disbelief. I had HEARD the shot, but I couldn't believe that it had gone off!  It had. Immediately a big silly smile broke over my face, and I fired several more rounds. Same result. FINALLY! I had discovered the last key.

The thing is that this shooting position is not comfortable under normal circumstances. It forces one to hunch down and crane the neck to get behind the optic. I partly solved this by installing a riser under my optic and pushing it forward. It's still a little bit "hunchy" but I can rip off shot strings like I'm shooting a 10-22.  Even using full power, 77 grain,  5.56 loads. Amazing.

For longer shots, I usually pull the butt back into the pocket and assume a more comfortable, traditional position. But for ripping off quick shot strings CQB style, the other position rocks.  If you've seen images of SOCOM guys shooting, you might remember how kinda hunched up they look. It's a bit awkward, but worth it in order to pop shot after shot on target with no delay or loss of sight picture. If you were blazing away at short range at another guy blazing away at you, first one to hit would almost certainly win. This technique could give you a BIG advantage.  

If you haven't already done so, just try it.

Wordmahn

Excellent write up!

Thanks, freqlord.  I REALLY appreciate that.

I hope it helps someone get there easier than it was for me.

Good write up, thanks for posting!

OST

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Old School Tag

Well done OP

Oh. I learned something new. Ha!  Thanks, LastRites.  

Nice post wordmahn. There's a lot of overlap with my post here, you should give it a read:

http://www.ar15.com/forums/t_3_128/716328_The-Physics-of-AR-15-Recoil-Reduction.html

Thanks, pebble. I just read your posts on the subject. A lot of great info! You went into a lot of the WHYS, while I attempted to mostly outline the WHATS, just to keep it short.

The WHYS are very interesting to engineering geeks like me.  In my research I was initially confused by the conflicting claims of heavier buffers and BCGs vs lighter. Very confusing. There's a lot going on in there and it gets even more complex when one starts considering how it all plays out in PERCEIVED recoil vs actual recoil.

I think it would require even more explanation than your quite detailed treatment gave, to fully explain it all, but you made a good contribution. Not sure that my physics fu would be sufficient to do much better than you did. The why part is definitely not as simple as it seems. I ultimately sided with the light side. If I were setting up for a two year deployment in the sandbox, I would probably rethink everything.

Thanks for your input. I'm glad that you linked your article with mine. It would be great if they'd collect all this in one place and keep it easily available for reference.

Cheers!

I'm interested in the vltor a5. Couple of questions. With reciprocating mass being factor in recoil, is it best to go with lightweight buffer on this or the rifle weight buffer?  I also have a tubbs wire for my current setup, did you do the standard length one or rifle length spring because I know the tubbs standard is a lot longer than normal carbine. Lastly would the taccom rifle buffer work I assume in this?

Something else to keep in mind when taming muzzle rise, it's affected by overall weight of the rifle.

If you focus on building a lightweight rifle, you will experience increased recoil/muzzle jump.

I'm not saying I would add weight to a game gun, but I might not avoid it as much as I would with a rifle I planned to carry up a mountain.

When your using a lightweight carrier, you don't need as much reciprocating mass to tame bolt bounce.  I would go with an A5H0 buffer.

The taccom buffer won't fit an A5 tube, you would need to build a special spacer to prevent the gas key from impacting the receiver and still allow use of a rifle spring.

Good to know on lighter weight buffer. Taccom I believe makes a 2 piece rifle length buffer now so was curious about that in this setup.

I think you could cut the rifle version down so it would work.