reducing dwell time reduces pressure, which reduces the force applied to the action. less force on these parts means longer life, as they aren’t getting jerked and slammed around as hard. if you can slow down extraction, you can extend the life of the extractor. if you can reduce the force applied to camming of the bolt, you can extend the life of the bolt, etc.
Ok, thanks.
So is it safe to say, you can run and beat the hell out of a Middy 16" with less possible issues?
I in the middle of a build right now. When I get home (if I ever make it home:rolleyes:)I have a G&R tactical (95%) lpk waiting and everything else to finish my S&W lower. I want to build something I can run hard at classes, a HD role, or just shooting on weekends.
I’ve been wanting to use a M4 carbine upper. NOW I’m rethinking the build, may go with a middy 16" if the risk is less for tearing up bolt and bcg. 
It’s a trade-off. neither system is necessarily superior.
the middy is still pretty new, but that’s the theory. They do cycle smoother- that’s proven. This will lead to better durability. I’m not convinced, however, that middies are more reliable- i think a carbine will run longer hot, dry, and dirty than a mid in the same barrel length. obviously there’s still a lot of other variables involved- chamber size/condition, receiver/BCG play, buffer spring quality/condition, etc. I’m sure there are middies that will outrun carbines, but i think on the whole, carbines outrun middies. That extra power from a carbine system will cycle a weapon that would otherwise short-stroke with a mid system.
Reliability and durability are two seperate things.
The original 20" barrels left about 6.5" of dwell, which is basically perfect for that system. This approximate dwell length pretty much applies to carbines. with 16" barrels, you’re left with 8.5" of dwell, over-pressurizing the system.
this wasn’t a scientifically backed move- the reason we have 16" barrels with carbine systems is because 16" is the magical legal barrel length for civilian weapons, and the carbine system was the only existing system that would reliably operate a 16" barrel: handguards and gas tubes.
but now we’ve gone ahead and introduced the mid, which more closely reaches that sweet-spot with dwell- mosy middys’ ports (all but KAC, IIRC) are at 9.5", leaving 6.5" of dwell. 16" barrels should have mid-length gas systems.
theres a lot of debate about which way it should go, the shorter you get. this is why KAC’s mid is a little further out, shortening dwell. we also have to consider the amout of space between the port and the chamber, further complicating the question- the closer the port is, the higher the pressure of the gas as it enters the port, regardless of how long the bullet stays in the barrel after passing the port, compressing that gas. there’s a lot of evidence that you need to shorten the dwell from the magic 6.5" the shorter the barrel gets- thus, we have mid-length 14.5s, and we’re back where we started- do you want a little more pressure to ensure reliable cycling? or do we want a little less pressure to reduce havoc?
enter opinion.
bkb0000
Thank you for your wisdom.
Thats the info I’ve been looking for.
A mid is starting to make more sense for me on this build, because I want to stay in that 16" range.
Thanks again
If you’re going to get a 16" bbl, then use a midlength gas system …
… it’s simple.
So, is the reason that “14.5 inch” M4 has a “carbine length gas system” is to increase reliability under combat/dirty conditions instead of using a “middie gas system” which would make it shoot smoother, but lack some slight inherent reliability which the CLGS has?
I am a 14.5 inch guy and love the way that barrel length handles, ballistics, etc. but was wishing that my Noveske N4 Basic was not quite so violent (for lack of a better word) in recoil and so was thinking of getting a Middie 14.5 inch gun to get the best of both worlds, but as I understand I will lose (how much?) reliability?
Oh and am really enjoying this thread, I’m having one of those evolutionary speed leaps in my thought processes about the M4 with this thread (even tho it might not appear that way to others Thanks!
Never thought of it like that.
Thanks!
Would choosing a lighter buffer for a middy make a difference?
Lighter buffer = less resistance when cycling = less chance of short stroking?
Im not quite sure about that. In the last dust test where the M16 went against the M4 the M16 beat the M4 by quite a large margin in stoppages. The port pressures of the M16 are much less lower than a midlength as well.
Would choosing a lighter buffer for a middy make a difference?
Lighter buffer = less resistance when cycling = less chance of short stroking? [/QUOTE]
I have 4 middies and don’t run H buffers in any of them. I do run them in my carbines gas systems. The extra weight didn’t seem needed with the mids.
I also have a Noveske N4 Basic. I built it “for my wife”. She was nice enough to indulge me. I mentioned it earlier in the thread, I have MGI rate reducing buffers in my AR’s, including the Noveske. Got them from Brownell’s on the recommendation of our SWAT guys. It really has smoothed out the recoil, and been absolutely reliable. Down side is that it’s an expensive item. I don’t know how it’s going to hold up long term vs. a regular buffer, haven’t been able to find any info.
I agree with everything you’ve said here. Especially that reliability and durability are separate issues. Most people I run into fail to grasp that.
With an “over-gassed” gun like the carbine is said to be, it does seem that it would allow longer cleaning intervals as carbon builds.
Yes, BKB0000. Thanks for the informative lesson on the AR gas system. I think I have read about dozen books about ARs and service rifles and never seen anything about the specifics regarding the purpose/ design of the gas system for the M-4 carbine. Very good information.
SkiDevil
perhaps a good analogy would be that rifles push the BCG, carbines punch the BCG. the rifle system delivers a longer, slower, more even gas flow. the rifle system is less pressure- but the rifle buffer weighs almost twice as much as a carbine buff.
the 20" rifle system is the most reliable and durable system, between the 3 we’re talking about.
i think the biggest reason the M4 uses a 7.5" port is because, like with 16" barrels in the beginning, it’s what’s available. I bet the magic dwell spot for a 14.5 is probably closer to 8.5", by the math. but since the 7.5 works, and it would be monumentally expensive and time-consuming to make that 1 inch change, we run what’s been working.
I am a 14.5 inch guy and love the way that barrel length handles, ballistics, etc. but was wishing that my Noveske N4 Basic was not quite so violent (for lack of a better word) in recoil and so was thinking of getting a Middie 14.5 inch gun to get the best of both worlds, but as I understand I will lose (how much?) reliability?
and that is the big question… i dont know.
i would have no concerns running a mid-length 14.5 for a fun/training/SD/HD gun, because our personal weapons being used CONUS are well maintained, kept well lubricated with our loob of choice, and aren’t subject to the ever-fucking-constant dust-fine sand that blows everywhere in the Sandbox. i think for civilian non-war use, mid is probably even preferable, as they’re more fun to shoot.
but anybody’s guess is as good as mine as to what the actual difference is between the two, beyond improved durability and funness. i can only speculate, based on what i know about how DI works.
I don’t think that any gas system length has an inherent reliability advantage. There’s alot more involved with the proper operation of a DI gun. It’s a delicate balancing act more than anything else. You can over/under gas or over/under buffer either system and then you have to factor in different pressure ammo as well.
If your Carbine is harsh cycling, you may want to use a heavier buffer which seems to be the preferred (& cheapest) method. Also, LMT’s enhanced carrier vents more gas and delays unlocking the bolt, PRI’s Fatboy gas tube reduces the pressure of the gas before it hits the carrier by adding an expansion chamber to give the tube more volume, midlength gas systems move the port further away from the chamber to reduce pressure. From my understanding of the function of the weapon system these seem like the best options. They’re all trying to accomplish the same goal: slowing the cyclic rate down. The problem is that it’s possible to slow the gun down to a point where it won’t cycle reliably either. Remember that balancing act?
Thanks BKB000…that is what it sounded like to me (the trade off) I was just trying to figure out if I was splitting frog’s hair or there was a significant reliability difference.
As for violent recoil…I have always been a FAL shooter and think the FAL has light soft recoil and enjoy it, so the N4 does not have uncomfortable recoil it is just that violent gas attack on the BCG coupled with a VERY light weapon causes my sights to jump around more than on my FALs which is not what I was expecting on an AR especiall after having only fired rifle length ARs. I love my N4, but will probably start looking into a 14.5 Middie.
Great INFO! Love M4C
No.
It’s because the carbine length gas system was simply “carried forward” from the XM177 series of weapons; and was allowed for serving the purpose of mounting a bayonet … on what ended up being a 14.5" bbl.
I agree. Interesting information indeed.