What is the non gas related function of the gas key on a bcg in AR, can I remove a portion of it for use in a manual loading rifle?

[arakboss]

You still could just cut tube part off the top as it appears the square mounting base of gas key is what prevents rotation the way i see it with your pics and other diagrams I have looked at. I will reserve final judgement until I look at a physical specimen when I get home.

My plan was just to remove the portion of the top tube that would mate up with a gas tube if the rifle had one.

After looking at it again, the head of the cam pin rides in that slot as well so maybe that would prevent the carrier from rotating if the gas key was completely removed. My gas key is poorly staked so I think for education purposes I will pop it off tomorrow and see if it rotates. And I will try with and without the cam pin installed. My bet now is it will rotate with cam pin out and won't rotate with cam pin installed.

 

[titsonritz]

I still don't get what would keep the carrier from rotating inside the receiver if the gas key was completely removed. see pic the part of the gas key with tape appears to be what keeps the carrier from rotating.

View attachment 603415

OK I was in a hurry to go to lunch and wasn't quite picking up what you were putting down. From the picture in the first post I thought you were talking about the front portion of the key you have shown taped. That portion is used to direct the gas, but also note there is a step in the key, the smaller, forward portion goes thru the hole in the charging handle, the step or shelf is larger than the hole in the CH catch the CH as in pulled back, working the action. If you were to remove a portion of the key you'd want to leave a short portion of the smaller diameter portion to allow the CH to catch it assume you are still using the CH

I'm still not sure how, if any, the rear of the key prevents rotation. The original design of the AR didn't have the same carrier key setup as they do now and with screw having a torque value less than 5 ft.lbs. that not a lot of holding strength. This is definitely a bizarre question. What is your end goal here?

 

[Flymph]

I know why you're bringing this up, and you're wrong (it won't work for your intended purpose).
The barrel without a gas port and a dedicated manual feed upper is the closest thing you can get.

 

[titsonritz]

It sure looks that way but I will defer to Mr tits as he has way more knowledge than I on these matters.

Well I'll tell this, it's not something covered in armorer's school.

 

[arakboss]

I know why you're bringing this up, and you're wrong (it won't work for your intended purpose).
The barrel without a gas port and a dedicated manual feed upper is the closest thing you can get.

I am trying not to focus on the why would you want to's and instead trying to get to know the details of how these things work.

 

[titsonritz]

My gas key is poorly staked so I think for education purposes I will pop it off tomorrow and see if it rotates. And I will try with and without the cam pin installed. My bet now is it will rotate with cam pin out and won't rotate with cam pin installed.

I have PSA upper I've been been debate replacing key screw and stake properly and thought of trying it out myself. Be sure to report back if do this.

 

[arakboss]

OK I was in a hurry to go to lunch and wasn't quite picking up what you were putting down. From the picture in the first post I thought you were talking about the front portion of the key you have shown taped. That portion is used to direct the gas, but also note there is a step in the key, the smaller, forward portion goes thru the hole in the charging handle, the step or shelf is larger than the hole in the CH catch the CH as in pulled back, working the action. If you were to remove a portion of the key you'd want to leave a short portion of the smaller diameter portion to allow the CH to catch it assume you are still using the CH

I'm still not sure how, if any, the rear of the key prevents rotation. The original design of the AR didn't have the same carrier key setup as they do now and with screw having a torque value less than 5 ft.lbs. that not a lot of holding strength. This is definitely a bizarre question. What is your end goal here?

I thought that too, about the gas key tube catching on the step in the gas key tube in order to draw the carrier back but after closer inspection it appears that the charging handle catches on a shelf machined in to the carrier itself. I will be able to confirm this tomorrow when I try to charge the rifle with no gas key installed. Stay tuned.

See in pic one below the shelf that the charging handle catches on to draw it rearward.


Pic two shows wear step in tube is and it would not make contact with charging handle prior to charging handle engaging shelf in pic one.

 

[Member 34319]

@arakboss take a look at non gas AR15 bolts. Like blow back 9mms. They have a key of some sort to ride within the upper receiver channel as a guide and remain functional with the charging handle.

I'm uncertain to why you wouldn't just remove the gas tube vs cutting up a perfectly good bolt carrier.

You might be able to run a piston BCG with a gas tube in place to not have to remove or cut anything. However if you run a piston carrier or a cut carrier and fire the weapon the gas will still blow into the receiver.

I'm confused to why you are not looking at the gas block or barrel to remove the "gas" part of the semi auto.

 

[titsonritz]

Here's a photo of an early AR bolt. Note the difference, but I there is a portion that could still serve as anti-rotation.

 

[arakboss]

@arakboss take a look at non gas AR15 bolts. Like blow back 9mms. They have a key of some sort to ride within the upper receiver channel as a guide and remain functional with the charging handle.

I'm uncertain to why you wouldn't just remove the gas tube vs cutting up a perfectly good bolt carrier.

You might be able to run a piston BCG with a gas tube in place to not have to remove or cut anything. However if you run a piston carrier or a cut carrier and fire the weapon the gas will still blow into the receiver.

I'm confused to why you are not looking at the gas block or barrel to remove the "gas" part of the semi auto.

My rifle will not have a gas port, gas block or gas tube. The only remaining portion that could be considered part of a gas system would be the gas key. If it's not necessary I will just remove it. If it serves another purpose besides directing gas then I would like to make it permanently inoperable as a gas key.

That is a good point about 9mm bolts. A member over at AR15.com pointed that out too and provided this link of a bcg with a minimal amount of material in place of where a gas key would sit on normal carrier: Extreme 9mm bolt


This is the description for gas key replacement on this 9mm bcg: "Next, we did away with that heavy gas key and replaced it with a low drag, low weight orientation key……all that key does is keep your bolt from rotating, nothing else. No need to stake these bolts, you have 1/5 of the original key weight so it will not become loose and it will not shear your screws."

 

[arakboss]

Here's a photo of an early AR bolt. Note the difference, but I there is a portion that could still serve as anti-rotation.



View attachment 603428

I think this photo settles it, the bottom portion of the modern day gas key acts as a anti-rotation part. I still plan on testing this out tomorrow but I am expecting to have to modify or replace the gas key with something else rather than just removing it. Thanks for posting that photo.

 

[osprey]

Ok I have looked an Ar upper over in the flesh and I believe the base of the gas key does prevent rotation.

 

[arakboss]

As a replacement for the gas key, I might be able to find some ball bearings that fit the width of the receiver slot where the gas key rides and could be screwed in to the locations where the two gas key screws went? That's assuming that the gas key isn't also needed for charging of the rifle. I'll determine that tomorrow. Thanks to everybody for the help.

 

[arakboss]

All the 9mm carriers I have looked at, have some type of part where the gas key would go. Many look like a regular gas key with the front tube part whacked off. Like this one:

 

[Jcon268]

How will you be cycling the bolt absent the gas key?

 

[Jcon268]

All the 9mm carriers I have looked at, have some type of part where the gas key would go. Many look like a regular gas key with the front tube part whacked off. Like this one:
View attachment 603433

Because that protrusion is what catches on the charging handle whether it be rear or side charging.

 

[Jcon268]

Cam pin serves as part for rotating the bolt when going into battery or I might be mistaking the question.

 

[turq]

If it was my project I would just contact Young Manufacturing.
They will give you the best excellent professional advice.

 

[arakboss]

Because that protrusion is what catches on the charging handle whether it be rear or side charging.

I don't believe that the gas key or protrusion in the 9mm bolts is related to charging handle function. I did think that until closely looking at it today. I will find out tomorrow after I remove the gas key. My belief now is that the little shelf on the carrier is what the charging handle grabs on to to draw it rearward and also draws the charging handle forward when released. See pic.

 

[arakboss]

Cam pin serves as part for rotating the bolt when going into battery or I might be mistaking the question.

You are right about that function of the cam pin. I was just observing that it also rides in the same channel that the gas key rides in and may also keep the carrier from rotating.