BCG weight and dependability

[King Chicken]

Heyo. After spending weeks reading about BCG weight and dependability, buffers, adjustable gas blocks I'm stuck. Im building an AR .556 and am just getting parts list together...
Can anyone spell out for me (as you would a toddler) if I can have a lighter BCG (either lightweight or much lighter than usual) , use buffer and adjustable block...and have the same reliability (changing ammo, shooting dirty) that I would have using BCMs bcg or something like that.
I've read apocalypse guns should use heavy bcgs for dependability but also read you can tune the gas to not make this a problem. Tuning for weakest ammo while dirty and heaviest ammo while clean kind of thing...

My goal is less weight for recoil and to combat the heavy barrel adding weight.

Spanks for the jam

 

[smokey]

m-16 carriers, adjustable gas blocks, and a flat wire spring. The mass of a heavier carrier is better for slamming forward through grit or a round that doesn't want to strip from the mag for whatever reason. Rifles built for reliability also tend to be heavier with gas to chug through if they're crudded up.

Lightweight carriers CAN be reliable with one specific load, but are less so if the ammo you feed them changes. They're less forgiving outside of their happy operational range. They are cool for running with less recoil and a faster overall action. There's also gas lengths/barrel lengths that come in to play. For instance, a mid-length system has advantages for a 16" and even 14.5" barrels now. A carbine gas system will likely be more sensitive to tuning issues.

These are all generalities though. It's best to go with a reputable manufacturer that has properly built and tested all components if reliability is what you're after. Picking up an upper from aero isn't too expensive for the peace of mind you get. Grabbing one from BCM is even better for some more loot.

Also, if you want less weight overall, a carrier is a bad place to look to cut it. Just get a fluted barrel and look for lighter weight handguards/stocks/optics.

 

[atblis]

Truth is somewhere in the middle. Lightweight carrier with a normal weight buffer out of a 16” mid length is still pretty reliable. Could probably take a little out of the buffer, and still be okay.

 

[alucard0822]

You have to understand the balance of things, and the tradeoffs with gas and mass tuning. As soon as the bullet passes the port in the barrel, gas feeds into the system, it stops soon after the bullet exits the muzzle. During that time(aka dwell) a certain volume of gas at a certain pressure is fed into the carrier through the key, it forces the bolt forward, the carrier is pushed back, this unlocks the bolt from the extension for a tiny distance of powered movement, gas then is exhausted from the side of the BCG out the ejection port. Inertia alone keeps moving the carrier and buffer rearward against the recoil spring until it ejects and reached the rear of the buffer tube. The spring alone then forces the BCG and buffer forward, stripping a round from the mag, feeding it into the chamber, latching the bolt to the extension, and engaging the extractor over the case rim.

Dwell or how long the gas is available is fixed by the distance between the port and muzzle. Pressure is regulated by the gas port size, the location(shorter gas systems have higher pressure available), and potentially by a restriction in an adjustable gas block. The volume of gas is a function of pressure and dwell, aka how long gas is fed, and at what pressure. This is gas tuning, you need enough gas to cycle, but too much can push the carrier too hard, can increase recoil, reduce reliability or increase noise and gas blowing in your face. The adjustment of this at any point, either by restricting or leaking gas contributes to the "gas tuning". Leak too much gas, and a rifle won't function, too large a gas port, and it can be overgassed etc.

Mass tuning is simpler, the more mass aka bolt and buffer weight that resists the gas force, the more consistent it's speed, and the more gas that can be fed without adverse overgassing. There is fixed weight, aka the BCG and buffer body, and floating weight, the weights inside the buffer. All of the mass resists the rearward movement, and helps increase momentum to plow through a dry or dirty action, but floating weight smooths recoil and resists bolt bounce.

Some things happen as you change gas pressure and fixed/floating weight. The heavier the weight, especially floating weight, the more consistent BCG speed is over a wider range of conditions, the more gas you can run, and the more reliable a rifle will be when dirty. This is why for a rifle that will be used defensively, or even a range rifle, you want a M16 profile carrier and heavy buffer. Often times with a 16" with mid-length gas you can run an H-H2(3.8-4.6oz) and have an ideal setup that will be reliable without an adjustable gas block. Some shorter builds can benefit from an H3(5.4oz) buffer, and may even run well with the added pressure/dwell from a suppressor, although that is where the ability to reduce pressure with an adjustable gas block can be useful. Recoil can be soft and mild as the bolt is moving at a comfortable speed, but the sheer mass can move sights around on target a little more.

Reducing mass requires less gas as it takes less force to push the lighter carrier/buffer back. While a standard M16 BCG weighs about 11.6oz, and usually runs with a 4.6oz H2 buffer, some BCGs can weight 8oz or less, and using just a buffer body with aluminum weights at 1.5oz can reduce the force of the carrier moving around SUBSTANTIALLY. add on an effective muzzle brake, reduce gas just enough to power it, and the sight moves very little when fired, and there is practically no recoil. This is ideal for competition, but the gas must be tuned just right as any small changes, even in weather or temp can push that BCG too fast, or too slow and jam. As greater mass makes the BCG more consistent over a range of conditions, lighter mass makes it less consistent and tuning it frequently becomes critical to be reliable. It's a different purpose, different strategy, and does have some benefits and drawbacks.

 

[Alea Jacta Est]

Paging the guru…Lord Chad please weigh in.

 

[SkiPatrolDude]

Proper mass is essential in ensuring sufficient momentum to keep the system reliable.

When you start messing with mass, after a point, no matter what the gas-efficiency of your rifle is, you will have problems.

Competition guns will sacrifice reliability and run ultra lightweight buffer/BCG set ups because those guns are only run squeeky-clean and with relatively low round counts and underpowered ammo.

 

[trickg]

Wow. You're way overthinking it compared to how I've done my builds. I get all basic level stuff - standard weight FA BCG, basic non-adjustable gas block, etc.

Regarding recoil, that's not something to worry too much about IMO - the AR15 is pretty kind where recoil is concerned because of it being gas operated and with the way the buffer tube is set up. You'd probably have more of an effect on muzzle control and recoil by using a muzzle device designed for that. With that said, don't take my word for it - I use cheapo A2 birdcages on all of mine. They seem to get the job done.

 

[RRomig]

Walking for hours with a 14lb rifle I’m also looking to shave weight. I started with a lighter scope , suppressor and barrel. I’ll try that for a bit to see where I’m at but I have been looking at skeletizing the receiver and bolt carrier.

 

[SkiPatrolDude]

Walking for hours with a 14lb rifle I’m also looking to shave weight. I started with a lighter scope , suppressor and barrel. I’ll try that for a bit to see where I’m at but I have been looking at skeletizing the receiver and bolt carrier.

Pretty hard to hit 14lb with a modern AR... no matter what's on it.

I could prob do it with an HBAR and a DD RisII rail and a massive scope, flashlight, backup irons, etc, but I would have to actively try to get something, even md compliant, that heavy.

 

[King Chicken]

m-16 carriers, adjustable gas blocks, and a flat wire spring. The mass of a heavier carrier is better for slamming forward through grit or a round that doesn't want to strip from the mag for whatever reason. Rifles built for reliability also tend to be heavier with gas to chug through if they're crudded up.

Lightweight carriers CAN be reliable with one specific load, but are less so if the ammo you feed them changes. They're less forgiving outside of their happy operational range. They are cool for running with less recoil and a faster overall action. There's also gas lengths/barrel lengths that come in to play. For instance, a mid-length system has advantages for a 16" and even 14.5" barrels now. A carbine gas system will likely be more sensitive to tuning issues.

These are all generalities though. It's best to go with a reputable manufacturer that has properly built and tested all components if reliability is what you're after. Picking up an upper from aero isn't too expensive for the peace of mind you get. Grabbing one from BCM is even better for some more loot.

Also, if you want less weight overall, a carrier is a bad place to look to cut it. Just get a fluted barrel and look for lighter weight handguards/stocks/optics.

You have to understand the balance of things, and the tradeoffs with gas and mass tuning. As soon as the bullet passes the port in the barrel, gas feeds into the system, it stops soon after the bullet exits the muzzle. During that time(aka dwell) a certain volume of gas at a certain pressure is fed into the carrier through the key, it forces the bolt forward, the carrier is pushed back, this unlocks the bolt from the extension for a tiny distance of powered movement, gas then is exhausted from the side of the BCG out the ejection port. Inertia alone keeps moving the carrier and buffer rearward against the recoil spring until it ejects and reached the rear of the buffer tube. The spring alone then forces the BCG and buffer forward, stripping a round from the mag, feeding it into the chamber, latching the bolt to the extension, and engaging the extractor over the case rim.

Dwell or how long the gas is available is fixed by the distance between the port and muzzle. Pressure is regulated by the gas port size, the location(shorter gas systems have higher pressure available), and potentially by a restriction in an adjustable gas block. The volume of gas is a function of pressure and dwell, aka how long gas is fed, and at what pressure. This is gas tuning, you need enough gas to cycle, but too much can push the carrier too hard, can increase recoil, reduce reliability or increase noise and gas blowing in your face. The adjustment of this at any point, either by restricting or leaking gas contributes to the "gas tuning". Leak too much gas, and a rifle won't function, too large a gas port, and it can be overgassed etc.

Mass tuning is simpler, the more mass aka bolt and buffer weight that resists the gas force, the more consistent it's speed, and the more gas that can be fed without adverse overgassing. There is fixed weight, aka the BCG and buffer body, and floating weight, the weights inside the buffer. All of the mass resists the rearward movement, and helps increase momentum to plow through a dry or dirty action, but floating weight smooths recoil and resists bolt bounce.

Some things happen as you change gas pressure and fixed/floating weight. The heavier the weight, especially floating weight, the more consistent BCG speed is over a wider range of conditions, the more gas you can run, and the more reliable a rifle will be when dirty. This is why for a rifle that will be used defensively, or even a range rifle, you want a M16 profile carrier and heavy buffer. Often times with a 16" with mid-length gas you can run an H-H2(3.8-4.6oz) and have an ideal setup that will be reliable without an adjustable gas block. Some shorter builds can benefit from an H3(5.4oz) buffer, and may even run well with the added pressure/dwell from a suppressor, although that is where the ability to reduce pressure with an adjustable gas block can be useful. Recoil can be soft and mild as the bolt is moving at a comfortable speed, but the sheer mass can move sights around on target a little more.

Reducing mass requires less gas as it takes less force to push the lighter carrier/buffer back. While a standard M16 BCG weighs about 11.6oz, and usually runs with a 4.6oz H2 buffer, some BCGs can weight 8oz or less, and using just a buffer body with aluminum weights at 1.5oz can reduce the force of the carrier moving around SUBSTANTIALLY. add on an effective muzzle brake, reduce gas just enough to power it, and the sight moves very little when fired, and there is practically no recoil. This is ideal for competition, but the gas must be tuned just right as any small changes, even in weather or temp can push that BCG too fast, or too slow and jam. As greater mass makes the BCG more consistent over a range of conditions, lighter mass makes it less consistent and tuning it frequently becomes critical to be reliable. It's a different purpose, different strategy, and does have some benefits and drawbacks.

Thanks for the extensive article. It really helps. The consensus I'm getting is that you cannot have warfare dependability with the fast competition style setups.

I had read that an adjustable gas block w/lite bcg allows to tune to fire/cycle the smallest round charge and the heaviest round...but over gassing seems to be vital for dependability.

Any recommendations to lessen the load of the MD hbar requirements? Who makes the lightest hbars 14"&16". Nooby here.

Thank you again!

 

[King Chicken]

Walking for hours with a 14lb rifle I’m also looking to shave weight. I started with a lighter scope , suppressor and barrel. I’ll try that for a bit to see where I’m at but I have been looking at skeletizing the receiver and bolt carrier.

I used to have to carry lots of weapons and weight in the desert. My rifle was generally not where the weight suffering came from thanks to my 2-3pt. rifle sling. I'd check some out. Slings ...thicker the straps/ the less weight per sq.in. on your body, durability, strength. Thickest of straps are harder to take off, hotter. I used thin. You get the collarbone bruise maybe but much faster/maneuverable.

Very heavy rifle though. Start a thread on lowering your rifle weight!

 

[alucard0822]

Thanks for the extensive article. It really helps. The consensus I'm getting is that you cannot have warfare dependability with the fast competition style setups.

I had read that an adjustable gas block w/lite bcg allows to tune to fire/cycle the smallest round charge and the heaviest round...but over gassing seems to be vital for dependability.

Any recommendations to lessen the load of the hbar requirements? Who makes the lightest hbars 14"&16".

Thank you again!

I have built plenty of both. My 3 gun builds have maybe 10oz at most between the BCG and buffer. I tune for 55gr FMJ and 69gr match handloads with adjustable gas, can run whatever power load I want provided I tune for it. Have run them in 500rd matches over a couple days, and they are reliable within that window, and run pretty well when filthy, provided I add a little oil every few hundred rounds. Essentially 0 recoil, and I can put pairs of shots within an inch or two pretty quick with the 1.5# Calvin Elite triggers I run. Problem is I have to adjust based on temp, and there is maybe a 4 click range on that gas block it runs well in. Meanwhile my defensive builds have run as many rounds as reliably, but pretty much never need to be adjusted if they are adjustable at all. You have to do everything right with either build type to be reliable or at least so they still run when a lot goes wrong. Comparing a comp build with a big obnoxious brake to a defensive build with a can or minimalist flash hider, the defensive has more recoil, but is still pretty smooth and handles well. For those I have adjustable blocks on, adjustments are less dramatic, and might run fine within 10 or more clicks, including wide open.

 

[outrider58]

In short, I would go with a 16" barrel with mid length gas, standard full mass BCG. H1 buffer with a "Whitehot" Springco buffer spring.

If you don't intend on shooting suppressed, there is little need for adjustable gas as long as you go with a middie barrel. It will be a softer shooting gun with great reliability.

 

[RRomig]

Pretty hard to hit 14lb with a modern AR... no matter what's on it.

I could prob do it with an HBAR and a DD RisII rail and a massive scope, flashlight, backup irons, etc, but I would have to actively try to get something, even md compliant, that heavy.

I used to have to carry lots of weapons and weight in the desert. My rifle was generally not where the weight suffering came from thanks to my 2-3pt. rifle sling. I'd check some out. Slings ...thicker the straps/ the less weight per sq.in. on your body, durability, strength. Thickest of straps are harder to take off, hotter. I used thin. You get the collarbone bruise maybe but much faster/maneuverable.

Very heavy rifle though. Start a thread on lowering your rifle weight!

AR10 platform
Heavy profile 6.5 20” barrel
ATN with range finder
Big stainless can
Came in at a fuzz over 14lbs
You are 100% correct a proper sling helps a lot.
I didn’t want to mess with that gun because it shoots unbelievable so I’ll probably sell it.
Instead I decided to dismantle another 308 I had and start over. I would’ve stayed with 308 to save that little weight but I have a ton of 6.5. Also a mag full would probably negate bigger hole in barrel.

 

[trickg]

Walking for hours with a 14lb rifle I’m also looking to shave weight. I started with a lighter scope , suppressor and barrel. I’ll try that for a bit to see where I’m at but I have been looking at skeletizing the receiver and bolt carrier.

I doubt that this rifle, once it's built, will be 14 lbs, and it's a 26" varmint contour barrel - it's a freaking barbell!

 

[GunBum]

If you have cash in surplus, you can have a heavy profile barrel that weighs much less…

AR-Type Barrels

Our AR-type barrels are designed with the goal of improving performance and reliability in the AR platform.

proofresearch.com

 

[smokey]

If you have cash in surplus, you can have a heavy profile barrel that weighs much less…

AR-Type Barrels

Our AR-type barrels are designed with the goal of improving performance and reliability in the AR platform.

proofresearch.com

Or just go for something like 300blk or 6.5 grendel/6ARC and not worry about the whole hbar thing.

 

[Magnumite]

Great post, alucard. Brief and to the point.

FWIW, if is a range arm...a compensator of some type will get to smoother shooting. My first 300 BO I assembled gave more recoil than I thought it would. Not a problem but not fast, if that would be what one is looking for. I sold it, the wow was gone. Enter another build. The used barrel came with a linear, forward gas propelling compensator. It works, reliabliity stayed 100%, too.

I then got a Miculek comp for the middy 16" 5.56. Very sweet. The comp may be the short answer to a recreational arm.

 

[King Chicken]

If you have cash in surplus, you can have a heavy profile barrel that weighs much less…

AR-Type Barrels

Our AR-type barrels are designed with the goal of improving performance and reliability in the AR platform.

proofresearch.com

Do you know if it's hard to find 14" .556 heavy profile but not actually high In weight. Nothing fancy(ceramic)...chromoly? Ty I am noob

 

[smokey]

Great post, alucard. Brief and to the point.

FWIW, if is a range arm...a compensator of some type will get to smoother shooting. My first 300 BO I assembled gave more recoil than I thought it would. Not a problem but not fast, if that would be what one is looking for. I sold it, the wow was gone. Enter another build. The used barrel came with a linear, forward gas propelling compensator. It works, reliabliity stayed 100%, too.

I then got a Miculek comp for the middy 16" 5.56. Very sweet. The comp may be the short answer to a recreational arm.

I have a strike industries jcomp on my 16" middy 5.56. It's cheap and awesome. It does a great job with reducing recoil, but directs gas far enough away from you that you don't really get blasted in the face like you do with a miculek type brake. It also does reasonably well at flash reduction for what it is.

5.56 Muzzle Brake / Comp / Flash Hider Shootout!

Testing 35 muzzle devices for the AR-15. A recoil-measuring test rig was created, and a recoil reduction winner has been declared! TTAG muzzle brake comparo

www.thetruthaboutguns.com

Annnd here's me with it in 3gun...