Shortest barrel length upper?

[LDB]

So many replies, so little responsive content. Thank you all for so much useful and helpful information.

[Eurodriver]

So many replies, so little responsive content. Thank you all for so much useful and helpful information.

The help is there, you just don’t want it because you’d rather fix a problem that doesn’t exist than go shoot the gun.

Let’s do this: You build your 16” rifle gas length upper and I’ll grab my 6920. Let’s run a course of fire and compare how we do. Just make sure that thing works in austere conditions - there will be dirt and water in your action by the end of it.

[sig1473]

Buy an 18" Rifle-Length and have it to cut to 16". I think this will be the only way to get the results you desire. Post and let us know your results.

[shiv]

So many replies, so little responsive content. Thank you all for so much useful and helpful information.

You realize you for the information you need? IG even said you can make anything run. It’s a matter of tweaking and tuning. I’m sure it will function with a huge gas port, but just because you can doesn’t mean you should. There are proven options. Any advantage you’ve cooked up in your head has already been R&D’ed. It’s an old system and we are where we are for a reason.


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[CPM]

Why do people **** around with proven systems for gains they can’t even verbalize? Just run a goddamn middy.


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That escalated quickly.

[markm]

I had an instructor who made a 16 inch gun out of a Colt rifle barrel that no one wanted in the Sheriff's office Armory. It ran fine.

For smoothness, however. Nothing beats the BCM 14.5" middy with an H buffer.

[Vegasshooter]

OP, I’m going to assume for a second that you are still new, or newer to the AR system. If I am incorrect, I apologize. The issue with running the rifle length gas system in a 16” barrel is the dwell time. That is the time from when the bullet passes the gas port, to when it exits the barrel. Think about this, the gun doesn’t start doing any work until the gas system is “charged”. Ie, when the bullet passes the port, and gas starts back to unlock the bolt. The entire process has to happen before the bullet leaves the barrel, and your pressure falls to zero. Once the bullet leaves, you have no pressure left in the system. I would think, and I’m not 100% here, but I believe you would have to run a bigger gas port doing it this way, due to needing a bigger/faster pressure charge to offset your shorter dwell time. By running a larger gas port to offset the shorter dwell, you’ve likely given up the soft, smooth recoil impulse inherent to the rifle length system. Therefore, the middy would, and btw does make more sense. I have personally seen guns set up like you are asking. Rifle length gas systems on 16” guns. The 2 I have seen, functioned fine. I don’t know what size gas port the barrels had. In this day and age, many companies run gas ports that are too big. This is so guys who insist on running crap ammo will have functioning guns when they shoot underpowered PMC or the like. If these guns had gas ports that started off too big, that would explain why the 16” rifle length worked. On a properly gassed barrel, I think you’d be on the ragged edge of reliability. You’d likely have to run a lighter buffer, and full power ammo.

In the end, it’s your gun, you can do as you please. Just remember that the system is set up to run inside certain parameters. Step outside those, and reliability may suffer. For ME....16”= middy, 18”= Rifle length.

[Cokie]

Buy a barrel with a rifle gas port and have a gunsmith cut it down to an 11.5" for you. Problem solved.

[odugrad]

Good explanation, vegasshooter.

[markm]

On a properly gassed barrel, I think you’d be on the ragged edge of reliability. You’d likely have to run a lighter buffer, and full power ammo.

I'd assume the OP would be running a rifle buffer system/stock. The instructor I know ran the standard A2 stock/buffer, and it ran fine. I think he did some port work. I thought I remember him saying .090", but someone here said the Rifle port is larger than that to start with... ??

In any case, yeah... with good ammo, as you stated, the 16" rifle will run.