Does anyone know of a company that makes a 16" barrel with a rifle gas system?
Maybe wanting something that isnt out there. But I would like to build an upper with a 16" CHF barrel with a rifle gas system and a F marked front sight.
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Does anyone know of a company that makes a 16" barrel with a rifle gas system?
Maybe wanting something that isnt out there. But I would like to build an upper with a 16" CHF barrel with a rifle gas system and a F marked front sight.
Not that I am aware of. DPMS has a heavy non chrome barrel that is 16 inch and rifle gas.
I wanted the same, had a 20 inch Colt Govt barrel that a friend cut to 16 and threaded with a .100 gas port that that worked fine with everything I have fed it. It does not have F marked FSB however. There are options but it gets into custom barrel work as far as I know based on my research. I was going to do a new barrel like a Sabre 20 and cut it in order to have the F marked base. But decided against it.
I have an Aimpoint on mine and have not messed with Irons yet. Depending on where you want zero sometimes it does not matter and a taller post can be added.....
From what I've heard/read that's the issue. The dwell-time for a rifle length gas tube and 16" barrel is too short, so you have to seriously open the gas port to compensate in order to get proper reliability. Unfortunately, doing so pretty much negates the benefit of using a rifle length gas system IMO.Quote:
had a 20 inch Colt Govt barrel that a friend cut to 16 and threaded with a .100 gas port that that worked fine with everything I have fed it.
Mid-length is the way to go on 16"ers.
I'll try.Quote:
can you expand on that?
Dwell Time is the amount of time that passes between the moment a fired bullet passes the gas port and the moment it leaves the muzzle.
During the dwell time, the only place for the expanding gas of the cartridge besides pushing the bullet is out the gas port, through the gas tube, and into the gas key, which is staked to the bolt carrier group. Once the bullet leaves, the path of least resistance then becomes the much larger muzzle and you no longer receive any gas assistance to the BCG.
Obviously, on a shorter length gas system, there is more space (and therefore dwell time) between the muzzle and the gas port.
Several people (and companies) have tested the rifle length gas system with a 16" barrel and found it's dwell time insufficient to reliably cycle the action of an AR-15, using a standard gas port diameter (generally considered to be .062"). The rifle length gas port is simply too close to the muzzle.
The only way to compensate for this (besides using a shorter gas system) is to use a larger gas port so that more gas is passed through the gas tube within the shorter dwell time, producing a more powerful (and violent) gas assist.
Think of it this way:
In a rifle length gas system on a rifle barrel (12" gas, 20" barrel, .062" gas port) the gas backpressures into the action just powerfully enough for just long enough that the action cycles reliably without undue violence, shock, or parts wear.
In a carbine length gas system on a 16" barrel (6" gas, 16" barrel, .062" gas port) the gas backpressures into the action just powerfully enough for too long. The action cycles reliably, but with extra violence, shock, and parts wear.
In mike240's expanded gas port configuration (12" gas, 16" barrel, .100" gas port) the gas backpressures into the action too powerfully, but not for long enough. However, the added power compensates for the lack of time and cycles the action reliably, but with extra violence, shock, and parts wear because his peak pressure is higher than in any .062" gas port rifle. It's the equivalent of a slap, instead of a gentle but firm push.
The ideal configuration, therefore, is a Midlength (9" gas, 16" barrel, .062" gas port) which, like the rifle length system with rifle barrel, uses just enough power for just long enough to be reliable while still being softer shooting and gentler on the parts.
If the reason you're considering a rifle length gas system on a carbine is for the enhanced sight radius, you could do a "Dissipator" build, which uses a rifle length front sight base in front of a carbine or mid length gas system concealed in rifle-length handguards.
thank you...
I was thinking rifle gas system for softer shooting.
The "dissipator" can be made with a mid-length gas system and be softer shooting then a carbine length.
http://img21.imageshack.us/img21/986...barrel1zm0.jpg
Not exactly true. The port pressure is monumentally lower at the rifle port position compared to the carbine's port position. Typically you'll need a port in the area of .090 to add gas. But it's not the same as a smaller port in the carbine length with immensely higher PSI.
I agree.. The only reason to run a rifle length gas system on a 16" barrel is that you already have a barrel that you're going to cut down, and your only other option is to buy ANOTHER barrel.Quote:
Mid-length is the way to go on 16"ers.
Here's my Adco custom cruiser.
http://i210.photobucket.com/albums/b...g?t=1270508999
So what about an 18" barrel? what would be the better gas setup for that length?
You know DD is coming out with an 18" middy length pencil soon----
ChicagoTex, nice explanation.
Why, thank you.Quote:
ChicagoTex, nice explanation.
my rifle gas 16" .. has gas port of .110
runs everything i feed it .. reliably and smoothly.
i like it alot.
I've played around with gas port size and location quite a bit... you can get a 16" with Rifle Length system to run... but as I recall, all of the test guns were single shots when we froze them.
Short story is we did not spend a lot of time on the concept, because the 16" with Mid-Length will always be a better solution.
As for port size, location, dwell and all of that... seems a lot of folks don't get the "big picture"
The only real important pressure is the max/operating pressure inside of the BCG - that pressure is a function of the following:
Gas Pressure at the port
Port Size
Barrel diameter
Time the pressure stays high (dwell)
Lock Time - the time the BCG remains locked, while pressure is allowed to build
Changing any on of these will change the pressure in the BCG - and of course, changing any one of these will most likely mean one or more of the others needs to be changed to compensate.
Neither of the 20" M16A2-profile Colt barrels I had cut down to 16.1", crowned and rethreaded ran well with anything less than MX193/XM855 power 5.56mm. They also stopped running when they got a little dirty, the additional friction was too much. I'd clean it, it would run another 2-300 rounds, and then start short stroking. I had my gunsmith open up the gas ports to .105, and they cycled a bit more violently than I liked, and still didn't like Wolf ammo. Even then, the gun didn't like any USGI mags with anything less than full power, new springs. This was about 9 years ago, better mags weren't an option at pre-2004-sunset prices, and PMAGS were still in the future. Eventually, I just sold both barrels off with disclaimers.
I wouldn't do it again, it seemed there was no margin for error for weak mag or extractor springs, worn parts, filthy or dry internal conditions ...the gun only worked under ideal circumstances. It was a way to use a barrel I had gotten for cheap - even then, 20" barrels were not as in-demand- and was free to have cut down, as I worked with a gunsmith's shop on site.
I've used mid-length gas with 14.5" and 16" barrels with great success, and rifle gas with 18" and 20" barrels with similar success. I now have a 16" "Dissipator" clone from PSA, with mid-length gas tube under rifle length MOE handguards out to a FSB. It scratches my weird itch to own a 16" that looks like a cut down 20", and works as well as any other 16" Middy I own. Best of all possible worlds.
Well, it's 16" and rifle length gas .... but it's 308.
KAC SR-25 ECC
http://www.lincolndiagnostics.com/pu...AC%20MAMS1.jpg
I'm pretty sure Delton makes one of these barrels that you are looking for, however I agree with the above poster that you won't have proper dwell and will have an oversized gas port. Better in my opinion to go 16" with a mid length.
That doesn't exactly count...;)
I'm sure you were just teasing, but for clarity:
Each cartridge has a different pressure vs time curve.
For rifle cartridges, the peak pressure is similar, but the duration or length is the primary difference.
This curve directly affects the operation of the gas system and drives the optimal range of gas system lengths.
An easy example is the 300 BLK, which has one of the fastest/shortest curves of any cartridge we're interested in.
Useable configurations are pistol or carbine length gas system, even up to 16" barrel length.
The standard port for a 20" barrel is .093".
I think about the shortest I'd go again is 18". I have experience with 17 and 18" barrels and rifle length gas systems.
There's also the intermediate gas system available
Sent from my SGH-T999 using Xparent BlueTapatalk 2
Yes... we did an Intermediate gas system at Vltor, as I recall John offered it for a while - it was a very nice shooting 18" barrel really.
Kino, I wonder what PSI we're looking at inside the BCG? If port pressure is well over 20KPSI, how much of that actually makes it into the carrier? By the time it gets there, after having expanded into the volume of the gas tube and carrier expansion chamber, plus, by that time-- I presume-- the bullet has departed the barrel and barrel pressure is dropping......
I tell guys, just don't hold your fingertip over those carrier exhaust holes while firing.....:bad:
BUT..... I have held carboard right on top of them while firing to get a feel for how much hell is coming out of them-- all I got was some dark smudges, no holes blown through or anything like that. My guess would be that it is hundreds, not thousands of PSI in there-- at least it is greatly reduced from whatever port pressure is in a given setup.
Would not have guessed that much but..... I could only guess. Doesn't sound unreasonable.
I have cut a good many department A-1's to 16" and got away with it..... I thought. In test firing they were 100%. But test firing is not the same as a 1000 round class and does not take into account the condition of the rifle and all its component parts a year or five down the road.
It works as long as the rest of the gun / ammo symbiance (I think I just made up that word) is optimal. Sprinkle in some weaker ammo and/or worn gas rings that otherwise would have gone unnoticed, and they will be.... noticed, in the form of malfunctions.
So, I don't do that no more.
Ned,
what size gas ports did you use on those 16" rifles?
Ran them as-wuz. .093. I later opened a few problematic ones up to .110 and it helped, but.... it still ain't the same o'course. It's like, if .093 is good with what, 6" of post-port barrel, and .110 is OK with 2", then would a .224 gas port with 1/2" of post-port barrel work? The slow, steady feed is better and more forgiving than the one big push.
I, like Ned, have trimmed down a bunch of M16A1 barrels to 16.5" and had no problems. But, they were all used with, or planned to be used with, XM193, and not lower-powered ammo.
My inside sources told me the peak pressure of the carrier was more in the range of 1200 to 1400 PSI, but I will check.
Regardless of what the peak is, it does not happen immediately, and it is not the same as the pressure in the bore at the port. The time lag and duration matters.
Well you can get a BCG to actuate pretty smartly with shop air so it seems reasonable that at 10-20X that it would throw the carrier back hard enough to compress the buffer spring and cock the hammer.