Can you operate an AR platform "manually only"?

[MarkCO]

"Remove the gas key?"

Don't try this-really, really bad idea. 50,000 PSI coming down the gas tube into the receiver won't be fun at all.
Either remove and reverse the gas block or just move it far enough to occlude the gas port.

Pressure at the gas port is not even close to 50Kpsi. But yes, just appropriately close off the gas system.

[COSteve]

If the OP wants to shoot his AR as a single shot for the best accuracy, then he wants to disable the gas pressure so the bolt stays closed after the shot to ensure the best accuracy. He can remove the gas pipe, plug the gas port, or remove the gas key from the bolt.

If he wants to let the AR's action open but not chamber a second round, then he can go with Blindstitch's $40 bolt catch solution.

If he wants to have the option to do either, then an adjustable gas port where you can 'turn off the gas' completely is the best option.

[O4L]

Originally Posted by Mobuck

I have to agree with FM on this, it's virtually impossible to install a dogleg gas tube 180* off. If bent enough to enter the hole in the upper, the gas key would hit the end of the tube.

You would think so, but not in the case I mentioned.

The first thing I checked on the rifle was that the gas tube was aligned properly with the gas key.

Then I suggested that he remove the handgaurd and move the gas block slightly to see if that solved the issue.

Once the handgaurd was removed I noticed the gas tube looked odd, and it was indeed 180° out of alignment.

Reinstalled the gas tube correctly and it functioned properly.

[4V50 Gary]

I'd rather get a barrel that wasn't drilled for the gas port.

[COSteve]

But then you don't have the option to shoot it semi auto.

[Ibmikey]

Use an adjustable gas block providing an off option.

[johnwilliamson062]

I'd rather get a barrel that wasn't drilled for the gas port.

Yes, and I am quite sure they are available. Just call the custom barrel makers and request it. Any other way seems like a less than great idea to me. Making a hole and then trying to plug it in a 50K PSI system just doesn't seem like a great idea.