The SLR gas block is pinned and a KMR 10 installed. The suppressor will have to be removed to adjust the gas block but not a worry with a direct thread suppressor and intended use of suppressed only.
I will shoot some unsuppressed this weekend to break in the barrel. Hopefully get the stamp shortly.
Looking great with the rail. Nice touch!
Mine is shooting great unsuppressed on the 11th click on the SLR adj block, running titanium BCG and A5H2 shooting federal 55gr. Haven’t tinkered with other variables beyond that… Yet.
In general, a 11.5" mid gas 5.56 can run well with a dedicated can, but with all the variables involved that can lead to a reduced span of operation compared to a shorter gas system when that system is run without a can. Look at the difference in carrier speeds. Depending on what is used, the span of function could be very limited to what the end user could use reliably.
We would strongly disagree, having tested it exhaustively prior to releasing the barrel. Having a longer gas system, by its nature (lower gas pressure, longer dwell), produces longer life.
Yes, it can have a more limited reliable function zone, but we have not seen the bottom limit of it when adjusted and set correctly.
The war sport lvoa-s seems to run pretty reliably unsuppressed with an 11.75" mid. So it seems it can be done, and done well
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Maybe, I should have asked what the design intent is for this platform?
Knowing that gassing a 11.5" mid gas barrel without a can with lower port pressure ammunition results in port size range for a given action mass and system. Then also knowing that a 11.5" mid gas barrel with a can that tends to be at the higher cyclic rate change is added with higher port pressure 5.56 ammunition with the same action mass and system, another range of preferable port sizes results. The possible overlap between the 2 types of operation is much smaller in range than what could be had by looking at the same preferable ranges when the gas system for each is reduced somewhat.
What I’m not catching here is how, in the current form of the platform can a 11.5" mid gas 5.56 operate in a wide span of function for suppressed or not without knowing the can (if used?) or the ammunition? When the gas system elongates with the reduced action pressure dwell time, the rapidly depressurizing barrel can work well dedicated to certain circumstances. Making that item for general use may lead to issues, as the end user may use ammunition and cans that do not fit well with their function overall.
I would tend to hesitate against going against a conventional carbine gas 11.5" 5.56 for most without a can. I could see the possible advantages of the carbine gas +1" in a 50/50 type suppressed gun, but mostly for suppressed only. I would be hard pressed to recommend the mid gas length in those without a can, but it has the ability to work very well with a dedicated suppressor.
Those are the right questions.
To answer them roughly as they were asked:
Design Intent: To create the best-possible shooting barrel for suppressors (as almost all cans are warrantied for 11.5"). From there, we tested and experimented and found the mid works just fine. By going to the longer gas system, it makes recoil more pleasant, reduces wear, and slows down the cyclic rate - all good things.
Yes, a 11.5" mid can span the the reliable operation of most types of ammunition, including 40-grain rounds.
The issue is that most shooters are used to seeing a long section of barrel after the gas port. On a rifle gas system, this is preferable, as the lower port pressure requires more dwell. Going back to mid, carbine, and pistol, the actual amount of barrel needed past the gas port shrinks markedly. In a pistol gas system, you almost do not need any barrel and a “gas trap” system works as the pressure from the powder is so high in and of itself.
Same for carbine, but it needs about a 1" of barrel to operate reliably, and we did the same testing for mid, which is where 11.5" came from. Due to the pressure at the gas port, its all that is needed for mids.
To your thoughts, the window for optimal function is smaller, but the window for reliable function is about the same as most systems. Hence why we chose to open the port significantly, as that gives the shooter the ability to optimize, not relying on our choice of a gas port hole and in worst-case scenario for someone who does not want to go adjustable, it will work without issue (though may be “overgassed”)
Thank you, Ray- That’s the piece of the puzzle I’ve been missing! Dwell time has nothing to do with it. If it did, slower ammo would result in faster carrier speeds, but it doesn’t. It’s all about pressure and flow. It’s all about the residual pressure curve in the bore after the bullet exits the muzzle. A suppressor slows down the flow of gas after the bullet leaves, keeping the pressure up in the bore at the gas port longer. The same thing happens when the distance from port to muzzle is increased.
Think about it- Ammo that is loaded to lower pressure is slower, which in turn increases dwell time. Yet that same ammo gives slower carrier speeds and even results in short stroking.
Ammo using heavier bullets loaded to the same pressure as lighter ammo results in lower velocities which in turn results in increased dwell time, yet there is no noticeable increase in carrier velocity. With all the experimenting folks on this site do with port sizes, buffer weights and springs, it is in response to ammo pressure, not velocity or bullet weight.
It’s clear that it’s not about dwell time at all- It’s pressure and flow
Bingo. The port pressure at Mid is still quite high, which gives us flexibility on barrel length.
For example, 7.62x39, with lower pressure at that distance is not appropriate for mid 11.5".
I’ve known for some time it’s pressure & flow, not dwell time, but it wasn’t until I saw Ray’s musing that the final piece of evidence fell into place for me
Then why do so many people run the LMT Enhanced carrier? I thought it’s claim to fame is longer dwell time. btw… not doubting… just asking.
This is a good question. The confusion comes from using the term “Dwell Time” without defining what we’re talking about. The dwell time being referred to in this thread is the time it takes the bullet to travel from the gas port to the muzzle.
The dwell time referred to concerning the enhanced carrier is the time from when the primer is struck to the time the bolt begins to unlock. The increase in time is due to the extra length of the straight portion of the cam track in the carrier. The carrier has to travel further before the cam can start unlocking the bolt. This gives the case a fraction of a second longer to shrink away from the chamber walls before being yanked out. The bolt dwell time has nothing to with the bullet dwell time
Exactly. The enhanced carrier is probably more appropriately referred to as an increase in unlocking time or delayed extraction.
The term “dwell” can be correctly used differently to describe the correlations in time of different parts of the system as a whole. It can be used correctly to describe items like the “time” between the gas port and the muzzle, bolt over travel, initial carrier movement to initial rotational bolt caming, etc.
Action systems, in a basic level are driven by a gas impulse. The system acts on the energy delivered to it and stores it primarily in the action spring. Some energy is used in unlocking and extraction, the amount used depends on the overall timing of the system as a whole, as it it varies. Hammer reset and magazine drag can be considered fairly constant in a range. Unlocking and extraction can be dynamic, or varying depending.
The action system can only operate with the gas pulse applied to it. If it’s insufficient it causes issues obviously. If it is excessive, other issues arise. In the balance of the gas pulse presented, a span of operation can be observed.
Let’s keep this basic and say that there’s no can involved and a given of the base system. For a 20" 5.56, how do you determine the widest span of preferred function for a given gas port size and/or gas system length? You can start with the baseline and test with different combinations. When seeing results, you can determine if the span widens or narrows in terms of function. Most would agree that a wider span that includes reliability and durability would be preferable to one that reduces that span.
With a barrel length of 11.5" in 5.56, what gas system length and port size gives the wider or widest span of reliability and durability without a can? With a barrel length of 11.5" in 5.56, what gas system length and port size gives the wider or widest span of reliability and durability with a can? When comparing the two types, you can trend the data to see when the 2 are more similar or distant in port size and location.
There are other variables that can be added to the mix to improve function overall for the 5.56 11.5" in terms of spring, buffer, and carrier. That is better suited after determining some of the other basics.
Overgassing is a problem that happens with too much frequency in this system as an unfortunate band aid. The unfortunate solution to many is an adjustable gas block, but it is not possible for an end user without the proper equipment that is really needed to see if they can really achieve the point that they actually do have the span of operation for serious use.
@Mistwolf… I see what you mean now… I didn’t realize the two points of dwell. Thanks!
@tom12.7 – why do you say the adjustable gas block is unfortunate. If the system is usually over-gassed by nature and you can under-gas it to the point of failure then adjust it back up some. that would seem to me to be ideal rather than unfortunate.
IOW, like knowing you have a car that will go 120mph but only need to drive it somewhere in the 35-55 range with driving 5mph simply being too slow. Even if I had no speedo I know the car will go way faster than I ever need. It seems like while I might not be able to define the span of operation I can define the low end ( bolt won’t lock back ) and I can guesstimate my high range which most people seem to just say… “give it a 1/4 turn more.”
I thought the adjustable gas block was looked at as valid solution and not an unfortunate situation. Especially if you want to go can on, can off, different can, etc…
An adjustable gas block may have the ability to lead to a preferable to MRBS and MRBF, but there is no reason to believe that the users can do so with limited resources.
A proper fixed gas port is beneficial over an adjustable port most anytime, if the fixed port is in the proper span of operation.
The FN FAL had a great adjustable gas system. I don’t see them as a negative at all.
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The FAL can be a brass stretcher with it’s own issues. The context in this is the basic AR platform.
I guess that was my unasked question as well. Why is fixed beneficial over adjustable? Is it because of the lack of additional mechanical failure points or something else? that’s the part I don;t understand… ok well, a part I don’t understand.
so let’s say Fixed and with adequate test gear you have a desired range of 5 to 10 on a scale of 1 to 20. So you fix it at 7.5 and it’s considered the best possible. Now let’s say with adjustable you can guess it to 6 or guess it to 8 and you are in the span but obviously you will have to re-adjust before the perfect fixed one… But besides that, is there something else undesirable about adjustable blocks over fixed?