T91 Gibbz Side Charging Build

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ethanol
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Hello folks,

I have been decided to mate a T91 Upper with a Gibbz side charging upper receiver.
Because it's cool.

All is prepared for the build, only waiting on the T91 barrel nut wrench to arrive.
The elephant in the room is the bolt to bolt carrier group interaction, and the piston to bolt carrier group interaction.

Luckily the Gibbz system takes care of those issues quite elegantly.
1. The T91 bolt carrier works in the Gibbz upper, only modification needed is to use the Gibbz enhanced cam pin.
2. The Gibbz upper has a removable plug for the gas tube to accommodate the piston.

See attached Image.
Gibbz Side Charging Upper Receiver.jpg
I will post instructions and pictures of the build as it progresses to completion or failure.
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ethanol
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Okay folks,

An update:

1. The build is complete. There was one issue.
The handguard retainer that rests against the barrel nut has two wings that do NOT seat on standard AR15 upper receiver.
The solution is that you must cut down these wings, approximately 1/8" from each direction.
Cut Down Handguard.jpg
Sorry for poor angle, if anyone is interested I will retake photos and add specific measurements.

As for the rest of the build, everything went smoothly.

Here is the finished build below:
Finished Build.jpg
Footage of test shooting will be uploaded later.

If anyone has questions, please let me know.
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e292644
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How do you taking care of the piston rod area on the upper receiver entry?
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ethanol
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The Gibbz Side Charging receiver has a threaded hole in the front of the gas piston / gas tube area.
For a DI gun, the builder must screw in a gas tube bushing to snugly hold the tube in place.
For a piston gun, the builder must screw in a gas piston bushing to snugly hold the tube in place.
The rifle WILL shoot and cycle without the bushing, but doing so will probably mess up the threads.

This is the gas piston bushing:
gas piston bushing.jpg
And this is where / how it's inserted:
inserting the piston bushing.png
With this installed the steel piston will ride inside of the brass bushing. I have ordered one and it is on the way. I will post an update as to how well the piston fits inside of the bushing, and if it will need to be drilled out to accommodate the 1/4" diameter piston rod.
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e292644
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Cool, that answers my question, let us know how's the final test result, can't wait to hear back from you.
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ethanol
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Hello all,

Back with another update.
I received the Gibbz upper piston guide bushing which installs easily into the front of the upper receiver, but there is an issue.
The piston bushing guide hole is too small to allow the T91 piston pass through easily. So it must be enlarged.

To properly modify it, I needed to drill out the guide hole to approximately 7/32".
Which is measured by the insertion of a 7/32" brass punch, the punch should have a little slack in it.
Advanced measurement system.jpg
Below is the front image of the upper after reinstalling the piston guide.
The face of the beast.jpg
Once that was done, I reinstalled the piston assembly and test fired it last weekend.


The gun ran just fine without issue, absolutely zero failures during shooting.
I don't see the need to modify the gun any further to meet my needs, other than feverdreams of someday installing and modifying a bufferless BCG so that a folding stock could be affixed.
I love this gun and it is my favorite AR that I have ever handled.
Will create a video of shooting sometime.
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Awsome! thanks for sharing.
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apex
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ethanol wrote: Wed Jan 12, 2022 2:10 pm Here is the finished build below:
Finished Build.jpg
Woah-ho-ho is that a FAL muzzle device???
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ethanol
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Yes, it is a DSA made FAL style muzzle device for 5.56 with 1/2x28mm threads. Cool looking aint it?

Anyways, I've decided that to take my build to the next level, I am seeking to put this entire upper on a SCR Fitelite lower.
Looking around to find one for sale as the manufacturer is frequently out of stock.
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apex
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ethanol wrote: Wed Mar 16, 2022 11:17 am Anyways, I've decided that to take my build to the next level, I am seeking to put this entire upper on a SCR Fitelite lower.
Looking around to find one for sale as the manufacturer is frequently out of stock.
That uses a proprietary carrier- you're going to have to change out the gas key for a piston "tombstone", and I think only Adams Arms made that part but has been discontinued for a while now.
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ethanol
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So after thorough research, you are correct.

However, I decided to make my own gas key strike face in CAD and machined it on CNC.
The prototype version is currently installed on the SCR lower's BCG, but I will be designing a superior one after some fire testing.
Piston Strike Face Simplified.JPG
I will recreate this to imitate the Adam's Arms which has the tongue on the bottom that fits into the gas port on the AR BCG.

I will post pictures when completed.
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Awsome work!
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