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…
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.
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.
Mid-length is the way to go on 16"ers.
can you expand on that?
can you expand on that?
I’ll try.
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.
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.
Mid-length is the way to go on 16"ers.
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.
Here’s my Adco custom cruiser.
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----
Be still my heart…that would be great.
ChicagoTex, nice explanation.
ChicagoTex, nice explanation.
Why, thank you.
my rifle gas 16" … has gas port of .110
runs everything i feed it … reliably and smoothly.
i like it alot.
Fun gun or defensive use?
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
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.