The combination that includes a proper port with the LMT enhanced carrier with the A5 action system alters the timing of events when compared to a conventional carrier and carbine action. The duration in time before bolt unlocking initiates is more, that allows the barrel to blow down in pressure more than a conventional carbine. The reduced pressure at that point has a few positive attributes. Another item is that there is more time present in the exhaust events before the key disengages the gas tube.
You get a smooth shooting system when you get a proper balance in the system. That could be done in many ways, that’s not exclusive to any the mentioned components.
Correct me if I’m wrong, but couldn’t the same be accomplished by increasing the reciprocating mass with a heavier buffer or carrier? I’m no expert on this, but I would think that a given amount of gas pressure would accelerate a heavier carrier more slowly than a lighter carrier, thus creating a similar increase in time before the bolt unlocks and the carrier key disengages the gas tube.
Yes, but then you need less gas to move less weight the other way. You get to much mass and spring then you get malfunctions from the system being out of balance.
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There are many balanced systems out there and many ways to make them. The amount of work used by the different types of systems to initially unlock the bolt and extract varies. That amount of work needed is in a direct relationship with how much the chamber depressurizes before those events occur.
An example of a balanced system could be an ultra light total reciprocating mass with a carbine type action spring, this system would take the most work, as it initiates the unlocking/extracting events at a higher chamber pressure. This would tend to be a less desirable balanced system, it is hard on parts, but it’s common on race guns.
Another example could be an LMT enhanced carrier with an A5H2-A5H4 type of balanced system. This system would require less work, as it initiates the unlocking/extracting events at a lower chamber pressure. This would tend to be a more desirable balanced system, it’s easy on parts (mostly), but some complain about an induced “wobble” from the higher mass.
When comparing the carbine action system to the A5/rifle system, a carbine action system cannot support the higher reciprocating mass that the A5/rifle system can support and maintain the balance. The additional mass adds to the delay and helps to reduce the amount of work needed.
When comparing the LMT enhanced carrier to a conventional type, the added delay in the cam pathway before unlocking initiates gives it more time for the barrel to blow down and require less work for the balance.
It seems to trend that the A5 with the enhanced carrier can have many benefits. There’s some things I would have preferred to change on both items, but those are commercially available now. I would like to see some advances in the future that are actually put in production.
The LMT enhanced carrier and a heavier A5 even benefit 20" rifle gas 5.56 rifles.
This is definitely the case. My Noveske Recon and light Recce barrels with LMT E carrier, Vltor A5H4, and green springco spring, cycles and locks back Tula .223. Every time. 1.) Noveske’s are over gassed. 2.) I am a big believer in the LMT e-carrier increasing the margin of reliability by reducing the amount of work required to extract the case due to chamber pressures dropping more before extraction which reduces the force of fiction of the case walls on the chamber walls (as you have made clear here and in other threads).
My go-to BCG now for reliability is LMT e-carrier, V7 Weapon Systems Cryogenic treated C158 phosphate bolt, V7WS 4310 melonite cam pin, and mil-spec chromed firing pin.
The slick coatings are cool but phosphate works well. All require lube and are only as good as the company standards that make them just like anything else. I like QPQ treatment and NP3. I’d like to see LMT do a e-carrier in QPQ.
It will be interesting to see what comes of 2A Arms new Cryoed, QPQ 9310 bolts.
Great info. I was not aware that Noveske barrels are typically overgassed. I had always had the impression that the gas ports were on the smaller end of the spectrum, similar to BCM.
I don’t mean to beat a dead horse, but the question remains (unless I’ve just missed the answer): is one method more effective than the other for increasing dwell time? In one corner we have a standard weight LMT E-Carrier with an altered cam path that allows the carrier to physically move farther back before bolt unlocking begins. In the other corner we have carriers that are designed to be slightly heavier than a typical FA M16 carrier, such as the Fathom Arms E-Carrier, which resist acceleration more due to the increased mass, also increasing dwell time. Is either of these methods superior to the other, or do they both accomplish the same net result?
I’m also curious about differences in carrier life between the two aforementioned bolt carriers. On one hand, the QPQ treatment on the Fathom Arms carrier increases surface hardness and reduces friction, which should greatly reduce cam path wear. On the other hand, I would expect the altered cam path of the LMT carrier to reduce wear as well due to less stress on the bolt during unlocking. Will one be more durable than the other, or is this one of these situations where it doesn’t really matter anyway because it won’t wear enough to matter?
^ This. I even inquired at LMT about procuring a batch of partially finished E-carriers (basically all the machine work done, right before hard chrome is applied to the inside of the carrier) about a year ago to send them off for QPQ treatment myself but was shot down cold. 
Yes, the A5/rifle action system adds more of a delay in initial unlocking than the LMT enhanced carrier when comparing the two to a properly gassed carbine action H2 system with the conventional carrier. The carbine action spring cannot support the same mass as the rifle action spring while maintaining the balance of function. When adding the LMT enhanced carrier to that system with a carbine action, it may be more durable to the bolt lugs, but the width of the span of operation can be highly reduced. Using the A5 type of system in conjunction with the LMT enhanced carrier can be broadened that to a satisfactory point. The LMT enhanced carrier tends to overspeed in carbine type action systems and runs into issues, as the applied gas becomes more than what is needed fully cycle that action properly, as the required work decreases. I would hesitate to recommend the LMT enhanced carrier in a carbine action application, it may be easier on the bolt lugs, but may have a narrower span of operation, it could be more durable and less reliable. I would NOT hesitate to recommend the A5 or rifle system properly weighted for most any AR platform. It is interesting to note that the combination of them can have very positive results in most any configuration when combined properly balanced.
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I think this would not work since phosphate carriers are machined to a spec which allows for the addition of dimensions when the inside is chrome lined. A nitrocarburized carrier would have to be machined to necessary dimensions since the treatment is not adding material.
In light of what Tom has elaborated I feel I should qualify that my use of the LMT e-carrier is always coupled with the A5 buffer system. The thing actually gives more uumph to the rearward recoil stroke otherwise. I think for a while it was thought to be lightening recoil by bleeding off extra gas perhaps even like the way carrier key regulation works but the thing actually lets you get away with less gas because less force is required to extract the case. Without either extra buffer weight using the A5 buffers or reduced gas at the port, you will likely notice increased felt recoil due to velocity increase as the altered cam pin track lets the carrier travel straight back longer before the cam pin is laterally engaged and when the bolt does unlock and tug on the case, the case is not grabbing back as hard, so the BCG bottoms out faster/harder unless compensated for.
Colt, BCM, Daniel Defense, LMT…my two cents…
I just bought this for my DDM4V5s from Joe Bob’s. http://www.joeboboutfitters.com/Daniel_Defense_CHROME_Complete_Bolt_Carrier_Group_p/dd-04-013-19135-043.htm