LMT Enhanced BCG question

[MistWolf]

If it is accurate that a small port sbr is the only concern, I'd would be interesting to see you turn yours down until you don't get lock back, then swap in a standard bcg and see what happens

Been there, done that. The standard carrier needed the gas port opened one click compared to the LMT Enhanced Carrier

[ScottsBad]

Wait. Maybe, I've been confused about the LMT Enhanced BCG... I thought that the LMT EBCG bled off more gas than a standard (say Colt or BCM) BCG? Is this not correct?

If that is the case; All else being equal, then wouldn't you need less gas to cycle a standard BCG? Since more escaping gas = less pressure in the BCG. Seems like the EBCG would be most beneficial in shorter barreled, over gassed carbine rifles, OR possibly longer barreled over gassed rifles?

It seems that the EBCG would be unnecessary (overkill) in rifles with mid-length (or longer) gas systems. Especially, with a rifle buffer system or A5 buffer system. Unless the rifle was way over gassed.

Isn't the danger of bleeding off too much gas that the rifle will not cycle when extremely dirty/gritty or when using degraded ammunition, or maybe in extreme cold with dirt and ice?

[Slippers]

Wait. Maybe, I've been confused about the LMT Enhanced BCG... I thought that the LMT EBCG bled off more gas than a standard (say Colt or BCM) BCG? Is this not correct?

If that is the case; All else being equal, then wouldn't you need less gas to cycle a standard BCG? Since more escaping gas = less pressure in the BCG. Seems like the EBCG would be most beneficial in shorter barreled, over gassed carbine rifles, OR possibly longer barreled over gassed rifles?

It seems that the EBCG would be unnecessary (overkill) in rifles with mid-length (or longer) gas systems. Especially, with a rifle buffer system or A5 buffer system. Unless the rifle was way over gassed.

Isn't the danger of bleeding off too much gas that the rifle will not cycle when extremely dirty/gritty or when using degraded ammunition, or maybe in extreme cold with dirt and ice?

tom12.7 is much better at explaining this, so I'm sure he'll chime in if need be.

The LMT e-carrier has a different cam pin track, which delays unlocking. A side effect to this is that the carrier moves rearward further before the cam pin is engaged, gaining additional velocity compared to a standard carrier. The timing window (for lack of a better term) is shorter, so the carrier doesn't need as much gas to operate, which is why it vents more.

[tom12.7]

There's more to it than that, but ultimately the LMT enhanced carrier doesn't require the same level in gassing to properly cycle compared to a standard carrier for most carbine type uses. There's always exemptions and trends in lesser details.

[BufordTJustice]

tom12.7 is much better at explaining this, so I'm sure he'll chime in if need be.

The LMT e-carrier has a different cam pin track, which delays unlocking. A side effect to this is that the carrier moves rearward further before the cam pin is engaged, gaining additional velocity compared to a standard carrier. The timing window (for lack of a better term) is shorter, so the carrier doesn't need as much gas to operate, which is why it vents more.

As Tom stated, there's a little more to it than that, but... Essentially, yes.

The way the gas propagates into the carrier and the toroidal gas expansion chamber is different, and it more efficiently imparts force into the carrier as well as permitting more efficient and faster venting of the gasses from that expansion chamber. The port that vents from the actual combustion chamber directly is different, changing the pressure curve inside the chamber. The additional momentum created by the longer cam pin track is also different.

The fact that the carrier, as a system, permits case obturation to more closely approach cessation, permits both a larger window of operation and less gas required to drive the system under most circumstances.

However, and Tom has noted this repeatedly in the past, going shorter than 11.5" approaches a precipice where the overall volume and intensity of the gas pulse MAY not be enough to fully drive the system in order to overcome the inevitable stiction force that the not fully obturated case is applying to the chamber walls. This correlates to, among other things, the length of barrel between the gas port and the muzzle, the blow down time of the system, even bullet weight, etc.

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[tom12.7]

We could go deeper into details. Some ask for more info about comparing other portions, as an example, swept volume vs constant volume within that specific portion as a system by itself. The expansion ratio is important, so is the exhausting of that, including items like condensates from that and where they are directed towards, etc. However, the above posting is pretty much a preferred guide.
The less than 11.5" 5.56 DI AR carbine gas limit really comes to a point into where most 5.56 users would either choose between into using that system only unsuppressed, or only suppressed, with specific porting for either.

[BufordTJustice]

We could go deeper into details. Some ask for more info about comparing other portions, as an example, swept volume vs constant volume within that specific portion as a system by itself. The expansion ratio is important, so is the exhausting of that, including items like condensates from that and where they are directed towards, etc. However, the above posting is pretty much a preferred guide.
The less than 11.5" 5.56 DI AR carbine gas limit really comes to a point into where most 5.56 users would either choose between into using that system only unsuppressed, or only suppressed, with specific porting for either.

Agreed 100%; under 11.5" and it's best to pick fully suppressed or fully unsuppressed for the gun's purpose.

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[ScottsBad]

tom12.7 is much better at explaining this, so I'm sure he'll chime in if need be.

The LMT e-carrier has a different cam pin track, which delays unlocking. A side effect to this is that the carrier moves rearward further before the cam pin is engaged, gaining additional velocity compared to a standard carrier. The timing window (for lack of a better term) is shorter, so the carrier doesn't need as much gas to operate, which is why it vents more.

Ok, so does that additional velocity add strain to the cam pin and cam pin hole? Anyone?

[BadgerPeak]

I'm not sure that's how I'd say it, but yes, the LMT enhanced track does introduce increased stress in a couple ways. With that said, I've not seen any failures, and there are a couple benefits that in my opinion, outweigh any concerns about increased stress.

[tom12.7]

Ok, so does that additional velocity add strain to the cam pin and cam pin hole? Anyone?

No, there are less stresses and strains. Unlocking at a later time allows pressures to reduce further. That allows a reduced torsional load on the cam pin/ bolt/ BE/ carrier/ upper receiver (at that location) during unlocking. This is different than mechanical wear/ cutting during feeding/ locking at the opposite of portions of most of these (not a portion of the upper), similar can happen during the first half of the action sequence.
To help keep the carrier velocities and other timing events in check, the carrier works better with rifle like action systems rather than carbine ones overall. Not that carbine actions will not run ok, but better with a more rifle like action for most all.
Starting with a properly gassed barrel, the LMT enhanced carrier, and a properly sprung and massed A5 action system, you can have a superior combination over the conventional carrier and carbine action by a fair margin for most carbines.
There are some things that I would have hoped that LMT would have done differently, but if used as prescribed, it's the best commercially available option at this time.