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Hello everyone 6.8 newbie here. I'm currently working on a 6.8 build and want to go with the vltor buffer system. Has anyone here used the DD 18" midlength barrel with a vltor buffer system? I was thinking of going with a5h1 and sprinco green but not really sure and came here for help! Thanks!
71958
 

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Anyone for the A5 system?
After much reading I have stuck with good ole carbine length tubes.
 

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Discussion Starter · #3 ·
Anyone for the A5 system?
After much reading I have stuck with good ole carbine length tubes.
From everything I read I saw quite a few people who loved the vltor system on the 68. However I wasn't sure how the gas port size aligned with others. The few I saw mentioned were .07xx or .08xx. I may just go with the carbine buffer system and call it a day.
 

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It's a shaw custom 350 legend barrel 1:16 carbine gas. I didn't have a pic of the DD barrel by itself. I had been looking for one for 6 months when I finally came across a descent barrel at OP. I'm slowly building up my ar hunting calibers. So far I have 6.5 Grendel, .224 Valkyrie, 300 BO, 350 Legend, and working on 6.8 SPC now. Going to do a 6mm ARC next.
 

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Hello everyone 6.8 newbie here. I'm currently working on a 6.8 build and want to go with the vltor buffer system. Has anyone here used the DD 18" midlength barrel with a vltor buffer system? I was thinking of going with a5h1 and sprinco green but not really sure and came here for help! Thanks! View attachment 71958
Welcome to 68.

We have 2 6.8s w/Vltor A5s on Aeros w/20' ARPs. Adjustable blocks are the Superlatives. Supercomp .30 Brakes. Very sweet to shoot.
 

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Thanks. What spring and buffer weight? And what are the gas port sizes?
They are stock A5 Vltor, never had to mess with them, and the gas is rifle length and whatever ARP's port diameter is. Again never had a problem. The Superlatives adjust from the front easy peasey. We tweaked them to just past 3:00, not quite 3:30 is how I would put it. Seems to be enough dwell to get the bullet out before the BCG rebounds. We set them up with S&B 110gr. If we need to change for AA2200 and CCBs we will. Takes two seconds with the Superlatives. They also vent to the front, another plus for me. If we had to size the port it wouldn't have been an issue either.
 

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I spoke with Daniels on their port sizing as a reference starting point for my last upper I built using their 16" S2W 1:11 5R barrel. They said they ported their barrels to run on full powered 6.8 SPC loads with a 3 o'clock ejection using a standard mass carrier an H1 buffer with a carbine spring which is pretty standard overall. Typical carbine gas system will eject closer to 2 with a similar buffer / bcg mass using full power or NATO spec loads.

They simply slow the carrier speed a bit by using an H1 buffer to keep a tighter velocity window by using more mass (mass regulation results in less drastic variations in BCG velocity shot to shot and the higher momentum conserves energy better for reliable cycling under heavy fouling, but at the expense of recoil impulse).

I run a lower mass BCG (8.5oz vs. 11oz standard) with my JP SCS configured for H2 weight, so total weight is about 1oz lighter than a typical carbine setup, but with more dead below from the buffer. I've found this configuration to be a really good balance between recoil impulse and reliability, it's more of an optimization on the standard carbine setup vs. something revolutionary.

Also, by using one piece gas rings and a NiB carrier, I need inherently less momentum for reliability because there's lower overall friction losses in the system. So I can achieve "standard carbine like" reliability that most tactical guys tout as the gold standard with less recoil from the action.

Neither traditional 3 piece gas rings nor traditional phosphate carriers are low friction by any means and the added mass (and energy) is required to overcome them to reliably go back into battery. That means more energy in the recoil impulse from the BCG that with modern optimizations isn't necessary any longer.

I'm only running the black 85% buffer spring (default spring weight for the SCS) and ejection is about 3 o'clock when standing. It locks back on last round even when not shouldering the butt stock. Gas setting is 9 from fully closed on the SLR Sentry 7.

Average velocity using 110gr Hornady OTM is 2584 FPS. over a 7 shot string, just a tad above the factory listing of 2570 FPS for this load.
 

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Send that DD back looks like its a 20" with a carbine length gas setup. Get yourself a ARP with a Mid-Length gas setup, If not in stock wait for one they are the best barrels for the 6.8 out there....
 

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I spoke with Daniels on their port sizing as a reference starting point for my last upper I built using their 16" S2W 1:11 5R barrel. They said they ported their barrels to run on full powered 6.8 SPC loads with a 3 o'clock ejection using a standard mass carrier an H1 buffer with a carbine spring which is pretty standard overall. Typical carbine gas system will eject closer to 2 with a similar buffer / bcg mass using full power or NATO spec loads.

They simply slow the carrier speed a bit by using an H1 buffer to keep a tighter velocity window by using more mass (mass regulation results in less drastic variations in BCG velocity shot to shot and the higher momentum conserves energy better for reliable cycling under heavy fouling, but at the expense of recoil impulse).

I run a lower mass BCG (8.5oz vs. 11oz standard) with my JP SCS configured for H2 weight, so total weight is about 1oz lighter than a typical carbine setup, but with more dead below from the buffer. I've found this configuration to be a really good balance between recoil impulse and reliability, it's more of an optimization on the standard carbine setup vs. something revolutionary.

Also, by using one piece gas rings and a NiB carrier, I need inherently less momentum for reliability because there's lower overall friction losses in the system. So I can achieve "standard carbine like" reliability that most tactical guys tout as the gold standard with less recoil from the action.

Neither traditional 3 piece gas rings nor traditional phosphate carriers are low friction by any means and the added mass (and energy) is required to overcome them to reliably go back into battery. That means more energy in the recoil impulse from the BCG that with modern optimizations isn't necessary any longer.

I'm only running the black 85% buffer spring (default spring weight for the SCS) and ejection is about 3 o'clock when standing. It locks back on last round even when not shouldering the butt stock. Gas setting is 9 from fully closed on the SLR Sentry 7.

Average velocity using 110gr Hornady OTM is 2584 FPS. over a 7 shot string, just a tad above the factory listing of 2570 FPS for this load.
We are using the VLTOR A5 and Toolcraft's DLC 6.8 BCGs w/ARP's 20" 3R rifle length with Superlative adjustable gas block. No issues using the S&B 110 at their factory anemic 2550fps without issue. When we rev it up with the CCB's 120 MKZ we expect none either.

Since you went 18" with a mid length I 'm not seeing a problem with the A5 and an adjustable gas system. A light weight BCG may throw in a wrinkle. Coatings matter too. The Melanited ARP Barrels are faster, and so are the DLC BCGs. Again the secret would seem to be a adjustable gas system.

Once you settle on a goto pill and load, then I can see playing with buffer and springs to lower gas volume and FHS in your receiver and recoil. I doubt we will bother. DLC and Melanie clean up easy. Supercomp XL .30 brakes work great on ours as built and tuned, since we don't have a recoil or target requisition issue.

Like ThELioN70x7 said you could go lighter and do w/o the A5. If building a Carbine I would go with ARP's 14.7" barrel w/Pinned Device and a Minimalist Stock, and build to that setup. Once things are settled down for us, that is on our to do list. We will never build an AR without a adjustable gas system.
 

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Versatility is the key because there's no practical way to know via theoretical calculations both the timing window (dwell time) and timing magnitude (average port pressure over that time) for a given load unless you have the ability to measure what that load does in a control barrel via something like pressure trace. So we are left with testing as we go and relying on known working configurations as starting points. Then we factor in BCG mass and friction as well, which varies depending on the lube used and carrier coating.

All of the modern alternative carrier coatings are good. NiB, DLC, Nitride, Chrome etc. are all much lower friction than phosphate. I went with NiB because one of the few low mass carriers I could find actually in stock was in NiB...not because it's superior in every way. It does happen to have the lowest friction of all types even if by a small margin, but from a pratical standpoint I doubt once could deduce a difference in practical application. Even the good old phosphate can work just fine, you simply need more mass and higher average port pressure to make it work, more frequent lube, but phosphate will ultimately result in an increase in system recoil from the BCG because you need more energy and mass to make it work reliably due to the losses.

The A5 buffer system however does not give you the ability to tune the BCG weights unless you buy different buffers from them (they offer carbine up to H4), but they do NOT offer tunable spring packs to match, they essentially set the spring energy storage capacity at that of a standard issue carbine spring and you tune the weight around that and your gas system. If you really want to optimally tune the system, you need to match both the total BCG weight along with the buffer spring energy storage potential to the gas port energy available.

If you have plenty of port pressure, I'm sure the A5 is quite good, but if you want to par it down, you at some point have to start reducing total system mass and spring storage energy. That's where low mass BCG's and configurable buffer systems come into play like the SCS. 5 tuning springs, 3 configurable weights from carbine (3 steel weights) up to H3 (three tungsten weights).

Adjustable gas blocks are critical to this just like mass and buffer spring rates, all three components are needed to tweak the gas system for a given load. Ultimately what the adjustable gas block allows is optimization of the energy transferred into the BCG for a given weight and spring rate, or if your satisfied with the gas setting (which determines the total recoil energy), you can re-shape the waveform via heavier or lighter.

The A5 system mentioned above is ejecting at 3, which means the gas port pressure is ideal for that buffer and spring weight. But if you use a lighter spring and buffer / BCG mass, you can reduce the gas pressure even more which reduces the actual recoil, then you figure out what spring weight and buffer mass give you the carrier speed you want at that port pressure. You have to balance all three elements, not just one or two and the A5 does not allow all three to be balanced without sourcing springs else where. Nor does it eliminate the harmonics of non-polished buffer springs and all of the polished ones from JP are extra power...so I think the SCS is still the best system for tuning when paired with an adjustable gas block of your choice.

My configuration is intended to capitalize on reduced friction losses to lower the components of recoil impulse as they relate to the BCG without moving too far into the realm of competition guns that require high maintenance and only run on one load in warm weather. I am running gas setting 9 of 15 with 15 being fully open, so 60% flow (or 40% restriction if you will). It also maximizes the dead-blow effect (in which all ke is transferred) since more of the mass is in the buffer vs. the BCG, maximizing system reliability at the given weight / energy level. If necessary, I can achieve a full 14oz combined BCG / buffer weight which is standard carbine if I wanted more system energy (for enhanced cyclical reliability) even with the low mass carrier (8.5oz vs. 11oz).

If you shoot a standard mass and gassed system with an A5 and then shoot my setup, your going to want to switch over because the impulse is lower than a system running an A5 simply because you need more energy to drive an A5 / standard BCG with GI spring than my setup, so you have more recoil. Conversely, if you threw an A5 / carbine spring and standard BCG into my upper with gas setting 9, it would short stoke, indicating inadequate port pressure, meaning you need MORE energy, not less. More energy in the BCG = more recoil.

And the A5's added length has NOTHING to do with recoil, it is longer because it goes up to an H4 weight, you simply cannot use a dense enough material in a carbine sized buffer to reach that much weight. So they made it longer like a rifle length system so they could get the weight up to H4 for severely over gassed carbines running hot loads.

SP-A5: A5 Spring and Buffer Kit | Vltor Weapon Systems

The magic of the A5 is to use mass regulation (H2 buffer) and has nothing to do with reducing recoil energy. JP has a great video on it called "Mass regulation vs. gas regulation". Weight (and spring tension) changes the rate of acceleration, average velocity of the BCG and momentum which re-shapes the recoil impulse wave form. More mass equals a longer and more drawn out impulse, but with a lower peak (the peak of the waveform is how people often perceive recoil), less mass equals a sharper but shorter impulse. So you can either have your sight move less but take longer to settle (more mass) or you can have your sight move more but take less time to settle (less mass)....or you can do what competition shooters do and reduce the actual recoil energy and achieve a reduction of BOTH which is more ideal assuming you don't wade into the realm of reliability issues for a given application.

This is why ALL top competition guns run low mass BCG's and adjustable gas blocks with as low a port pressure as they can get to cycle on their standard load, typically 55gr FMJ in 5.56. This is also why 9mm AR's are known for having MORE recoil impulse than most 5.56 AR's because the energy dumped into the BCG is more along with it's greater mass even if the cartridge muzzle energy is far less.
 

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And regarding barrels, I've run both Daniels and ARP, both in 16" 1:11 using the same load (110gr OTM). Both are great barrels with different focus. I've not found a difference in accuracy shooting factory 110gr Hornady OTM, but the ARP scout profile certainly suffers more accuracy loss from heat as it's not a heavy profile nor will the nitride steel handle the heat as well as chrome (higher working temps). So when you combine cold hammer forging (better barrel harmonics, lifespan and heat resistance), modern electro chrome plating (uniformity as good as a machined nitrided barrel with more than 2x the service life of traditional chemical etch chrome plating akak GI Spec) and a heavy profile (S2W), it's not only accurate, but incredibly consistent even when you throw heat at it.

ARP's barrels shine the most for handloads that hunt, low round counts = low heat. ARP's 3R rifling and chamber minimize pressure to maximize handload potential. For factory loads there's no difference at all and while I wanted to get into hand loading, time and cost have been prohibitive so I've stuck to factory loads from which there are plenty of good ones including custom loads like MKZ's which I'm going to do some chrono, accuracy and gel testing on in a few weeks.

There's a myth floating around that chrome lining isn't any more durable than nitride and less accuracy due to surface non-uniformity and that is generally true for GI spec chemical chrome process which is common for barrels in the $100 to $200 range and from smaller companies. But what about larger companies like Daniels Defense that have access to modern electro plating processes pioneered by Boeing?

Modern electro plating methods are far superior in terms of plating uniformity and avoiding micro-cracks that are common in the old chemical process. Those micro-cracs are why hard chrome degrades at about the same rate as nitride wears, you get fire cutting that widens those micro-cracks on the surface of brand new barrels that eventually degrades the steel below. Once you eliminate them with an optimized electro plating process, you can more than double the service life over traditional chemical etching process. The surface uniformity issue also goes away and is on par with cut barrels that are nitride.

This is why Criterion has chrome lined barrels that hold sub-MOA accuracy for 20k rounds or more. This is why Daniels Defense barrels in training carbines for LE agencies survive 30k to 40k rounds with 2 MOA accuracy. This is why Boing found that in aircraft gatling guns, the barrel service life of their proprietary "Boeing Chrome" process more than doubled the service life.

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While DD isn't using the same hand lapping process as Criterion (not as far as I'm aware), their more modern electro-chrome plating process is good enough that real world accuracy it MOA or Sub-MOA for their barrels but with ruggedness that far exceeds other suppliers for 6.8 SPC barrels. From a practical shooting standpoint, I think the other factors such as heat capacity, incredible durability and S2W profile make it a very balanced barrel design overall for it's application. My experiences mirror that.

My only gripe was having (by choice) to come up with a unique solution of using AZ61A magnesium handguards from JL Billet to off-set the added weight of the S2W heavy profile. But now on top of that, I have rifle that shoots like a bull barreled nail driver but handles like a standard carbine.
 

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