Buffer weight.

[Badger52]

Ballistic Advantage 11.5" Modern Series 5.56 barrel
Gas port, (best I can measure) .076 -.078

I would not be surprised if that barrel's port was .073, although may be .076. If it matters at all you can contact BA directly & simply ask them politely. I've found them very forthcoming in answers to direct questions from customers (vs. some companies for whom everything is locked up in the double-secret proprietary probation cabinet). You are correct that your bolt carrier weight has a stake in the game; it's part of the reciprocating weight. As others said, maybe start with H2 but then shoot & evaluate.

[99HMC4]

Sometimes people tend put to much emphasis on gas port size. It’s important, yes. But there is no fix all magic number either, there’s a range that is known to work. The gas port is only one of three components in the recoil cycle. It’s not always feasible to be able to pin your gas port, know what to do with that measurement and then do something about it. Be it drilling to a new size, welding and drilling to a smaller size or barrel replacement. Where as a buffer and spring, are simply drop in parts. And “most” of the time, can be dialed in well. We’ve found that 4oz buffer was the optimal weight for the LARB recoil buffer. We exclusively use Sprinco springs and prefer a slightly stiffer than “mil spec” spring. I personally prefer a slightly stiffer spring for going back into battery and stripping rounds from the mag. Basically the stiffest spring that will give you a good ejection pattern. And I prefer to stay around 4oz...

[MistWolf]

Sometimes people tend put to much emphasis on gas port size...

Buffers and springs won't fix an over gassed barrel.

[99HMC4]

Buffers and springs won't fix an over gassed barrel.

Sure it will, but to what degree is the issue. It’s not always feasible, nor necessary to change out an “overgassed” barrel. There’s no “one” gas port size to end all, that’s why we have diffent spring rates and diffent buffer weights, to do exactly that. To “fix”, fine tune and compensate for an overgassed gun. That’s what this whole buffer weight and spring thing is with the AR platform, one component compensating for the other until the combination of all the components at work (gas port, buffer and spring in the case of recoil cycle) function correctly together as a whole. So yes, a spring and buffer comb can “fix” an overgassed barrel to a degree. Or undergassed, it another words “tuning” the ejection pattern with buffer weight and spring is literally fixing an over/undergassed gun...

[99HMC4]

You also need to define “fix” an overgassed barrel. That’s very subjective. What does “fix mean? Do you have a number in mind that the port HAS to be, or it’s wrong? What if that number (for example ONLY), is .075. Say you have an AR that has a .075 port and it works perfect. No throw a muffler on it and the brass goes from 4 O’clock to 1 O’clock. Now that gun is overgassed. But how can that be when the port is the perfect 0.75? Now take that guns 3oz Buffer our and install a 4oz buffer. Now the brass is back at 4 O’clock. Now, wouldn’t that mean the buffer “fixed” the overgassed barrel? In this current configuration? This is a very broad and vague example, but it illustrates my point. I have done a tremendous amount of R&D/T&E on this very subject. Designing, testing and building the LARB recoil buffer has thought my SO much about the recoil cycle of the AR. Another way to fix the over gassing is an adjustable gas block, probably one of my favorite choices. But again, not always doable. The overgassing also effects more than just carried velocity rearward, but also forward, going back into battery. People don’t realize that the ejection/rearward part of recoil is only about 75% of the whole recoil cycle. The carrier/buffer going forward back into battery is the othe part of the recoil cycle equation, and also very important. That forward cycle is mostly spring/buffer, no gas port. Again, try not to focus on one thing like the gas port size (unless it’s like .125 hole, then yeah, it’s wrong) but rather take every aspect into account and then find a combination of components that work within good/acceptable range. And that range is generally pretty big....

[MistWolf]

Sure it will, but to what degree is the issue. It’s not always feasible, nor necessary to change out an “overgassed” barrel. There’s no “one” gas port size to end all, that’s why we have diffent spring rates and diffent buffer weights, to do exactly that. To “fix”, fine tune and compensate for an overgassed gun. That’s what this whole buffer weight and spring thing is with the AR platform, one component compensating for the other until the combination of all the components at work (gas port, buffer and spring in the case of recoil cycle) function correctly together as a whole. So yes, a spring and buffer comb can “fix” an overgassed barrel to a degree. Or undergassed, it another words “tuning” the ejection pattern with buffer weight and spring is literally fixing an over/undergassed gun...

One reason we have so many different buffer weights and spring rates is because some manufacturers either don't know what they're about or don't care if they get it right. You can't fix an over gassed rifle just by changing the buffer weight and/or spring rate without introducing other problems, such as bolt bounce or having too much unsprung weight. In this case the unsprung weight is the reciprocating mass. Think of it like an automobile. The axles, tires & wheels are the unsprung weight. The body of the care is the sprung weight. If the ratio of unsprung weight to sprung weight is too high, the ride becomes uncomfortable. If the unsprung weight is too high in an AR, it starts pushing around the rifle more than is desired.

...Say you have an AR that has a .075 port and it works perfect. No throw a muffler on it and the brass goes from 4 O’clock to 1 O’clock. Now that gun is overgassed. But how can that be when the port is the perfect 0.75? Now take that guns 3oz Buffer our and install a 4oz buffer. Now the brass is back at 4 O’clock. Now, wouldn’t that mean the buffer “fixed” the overgassed barrel?

You're kidding me, right? If a rifle is properly gassed unsuppressed with a .075" gas port and the shooter screws on a suppressor, no one is ignorant enough to think it will still be properly gassed. No one is ignorant to think that the proper gas port diameter for a rifle length gas system will be the proper gas port diameter for a carbine gas system. If you're gonna shoot an AR fitted with a 16 inch barrel using a middy gas system and no suppressor, you're gonna want a barrel with a larger gas port than if it were to be shot exclusively suppressed. If you want bot to work, you're gonna have to find a port diameter somewhere in between and and figure out what compromises you're gonna need to make.

While you can get a general idea of how well an AR is functioning by it's ejection pattern, it's not reliable enough to fine tune the system, especially if you don't start with a brand new in spec ejector, extractor and especially springs.

Gas port diameter is important- or more specifically, gas drive. If it's excessive, too much reciprocating mass will be needed to keep the rifle from battering itself and the shooter. Too little and the reciprocating mass might have to be reduced to the point that carrier speeds will be excessive to make up for the loss of mass. Reliable feeding requires a certain amount of momentum. Take away mass and speed will have to be increased.

The whole system requires balance between gas drive, spring rate and reciprocating mass. Gas drive controls gas pressure and flow. Pressure is affected by ammo type and port location. Flow is determined by pressure and port diameter. An over-gassed system is out of balance. Throwing a heavier buffer/spring rate at it doesn't restore the balance.

[99HMC4]

We’re kinda say the same thing, but with different emphasis. I agree about the unbalanced system, totally. But you have to realize that the buffer/spring combo is just as much (if not more in some cases) than the port in this system. As to your point, you can have a “correct” gas port, and throw in the wrong spring and buffer and unbalance the system the same. Also, you have to realize that in most cases, tuning the carrier velocity (which is where we get the “proper” ejection patterns as a guide, can be done with buffer/spring. Many cases, buffer only. Does that make it “wrong”? If you get the bolt velocity right, (witch is different in every platform) by way of mass, ie buffer, that’s okay. And it’s typically the cheapest and easiest. And again, that’s okay too.

[MistWolf]

We’re kinda say the same thing, but with different emphasis. I agree about the unbalanced system, totally. But you have to realize that the buffer/spring combo is just as much (if not more in some cases) than the port in this system. As to your point, you can have a “correct” gas port, and throw in the wrong spring and buffer and unbalance the system the same. Also, you have to realize that in most cases, tuning the carrier velocity (which is where we get the “proper” ejection patterns as a guide, can be done with buffer/spring. Many cases, buffer only. Does that make it “wrong”? If you get the bolt velocity right, (witch is different in every platform) by way of mass, ie buffer, that’s okay. And it’s typically the cheapest and easiest. And again, that’s okay too.

I agree, I don't think we're too far off.

I find that the buffer weight & spring are good for fine tuning. Using the AGB, I turned the gas down until the AR would eject, but not lock back. Then I'd open the gas block one click (SLR AGB) and the AR would eject and lock back. One click more would give it a little more oomph to plow through any schmootz build up or other variable, although I've not needed to do so, even suppressed.

Experimenting with the gas block showed that the AR used the same gas block setting whether I used a CAR, H or H2 buffer. Sometimes it needed to be opened a click when switching to the A5H2. There was a difference in felt recoil. With the CAR buffer, recoil felt sharp. It was smoother with the H buffer. It was even smoother with the H2 buffer and cycling was a little slower. Smoothest was the A5H2, but it felt even slower. I thought maybe too slow, but it still worked when firing fast.

Changing the buffer & spring may be cheapest, but until I got the gas drive dialed in, a heavier buffer/spring rate did little good. The over-gassed AR was reliable with the heavier buffer, but recoil was unnecessarily excessive.

When I first started with ARs, a friend had an AGB on a new AR and wanted to tune it. We tried using the ejection pattern, but it wasn't consistent enough to get a good read. Later, I realized I was having a complete brain fart. After all, I've tuned several FALs using the AGB. To tune a FAL, keep opening the Gas block (it's a bleed off style) until it ejects but doesn't lock back. Then close it until it ejects and locks back, then open it a click or three more. Done. Of course, it's difficult, if not impossible, to use the lock back check with a fixed gas port. But experiments with the AGB gave me an idea what an well tuned AR feels like.

I'd like to clarify about buffer weights. I think CAR buffers are too light and for carbine REs, the H and H2 are about right. If an H3 is needed, an A5 RE or rifle RE is better. I consider the H, H2 & A5H2/Rifle buffer to be normal weights, not heavy weights.

I also think that if something heavier than a H3/rifle buffer is needed, the gas drive must be scaled back. This is for 5.56/223 caliber ARs I don't have enough experience tuning ARs in other calibers to even venture a guess.

[99HMC4]

�� I’ve had customers want me to send them our A5 buffer with all tungsten weights. Imagine our stainless buffer, in an A5 length full of tungsten?! That’s like a half a pound buffer. Yeah, somethings wrong there.

[Tokarev]

�� I’ve had customers want me to send them our A5 buffer with all tungsten weights. Imagine our stainless buffer, in an A5 length full of tungsten?! That’s like a half a pound buffer. Yeah, somethings wrong there.

Can the LARB 2 be ordered with all tungsten? I'd like to try one in my DPMS G2 Recon.