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T91 AR Piston upper


Red Skull Member
May 20, 2020
Member Number
Triangle area NC
Just picked this upper up on another board. Was only looking for a set of hand guards for my A2 and...:laughing:


To me it feels more natural in my hands that the A2. The round hand guards and the carry handle sight on the A2 never really worked for me. The TY91 hand guards are tapered and shaped more like a FAL. Points well and I appear to be getting a better sight picture while maintaining a good cheek weld. We will see once I get to the range.

I was worried that as a piston driven upper it might be heavier but even though it is a 16" barrel and my A2 a 14.5" (heavy barrel) it is six ounces lighter. Only thing that is a slight detriment is the sight radius on the T91 is 14" and the A2 is 16.75. It came with a UTG rear sight that the PO put on it. But once I shoot it I may try something else.

Does anyone make a folding rear sight that sits further to the rear over the area not milled for Picatinny slots?


Interesting but pretty simple short stroke piston set up. Used by the Taiwanese military for a long time. Here is the military version which as a few subtle differences like a FSB with bayonet lug and a more angular pistol grip. They use a 14.5 barrel in conjunction with the bayo. Some people are going all out rebuilding theirs into military configuration. I am going to avoid scratching that itch. Especially right now as most of the parts are out of stock due to panic buying.

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I know it's not folding so doesn't fit your criteria at all but I bet a Scalarworks peak rear would look awesome on that.

I've always liked the T91 wouldn't mind putting one together
I do like the way that looks on the firearm and it does extend the sight radius to the rear of the upper. $150...ouch!

Honesty need to reconsider whether it needs to flip or not. Front sight is fixed but removable. Unless I upgrade to optics they can both stay mounted. The cheapo BSA red dot I have sits too low to cowitness. I could put it on a riser but might be time for a decent one.

Well, Hyde. You just cost me some money on ARF com. :laughing:

There were some NIB Scalarworks sights there. Full set for slightly cheaper than new. Rear alone was sold out at Scalarworks. Just about every decent sight was sold out on Midway too. So I jumped on them.
Got the Scalarworks sights in last night, after the USPS delivered it to the wrong house... Glad they found it.

Nicely made. Has to slide on to the rail from the charging handle side. The bolt cross pins through the rear Pic slot. It is not going any where.


Sets the Sight radius back about 1.125. over the slotless shelf behind the pic slots. So now just over 15. Just where I was looking to put it. Plenty of room in front for an optic mount if I go that way with this one.


Here is a pic looking down the barrel. I like it even better now. It has a very central balance point with a loaded mag inserted. Just under 7Lbs total. Thanks for the suggestion Hyde!


Now I will be figuring out a light mount off the right side of the handguard near the front sight. There is a stock tri rail available ($65!) but I only need one location so am going to experiment with some thick aluminum plate I have. There are two nutserts imbedded in the top of the handguard for the stock mount. I will see if I can home brew something simple and specific to my needs.
No sweat! Still haven't gotten to shoot it. My buddy with the range membership and I are waiting for a break in the heat.

Had the piston out the other day and took a pic. It is an interesting self contained unit. Comes out with no tools, which is nice.

Kind of similar to a FAL as it comes out the front of the gas block but unitized with the springs in a tube. Perhaps designed this way to work with minimally modified AR uppers. The front of the upper is milled to hold a non standard rear hand guard retainer that is riveted to the upper. The Barrel nut is different as well since it has to accommodate the piston.


Gonna bump this....Finally got my T91 on the range...it hates my 55gr hornady loads...what weights and group sizes have you got with yours?

For reference, my 10.5" AR will hold just under 2moa using a holosun dot with the same load, the T91 was more like 8moa...threw some 60gr sierras thru it and that got it down to 3.5....sigh
At what distance?

I've been shooting 55grn federal. But only really enough to sight it in. Iron sights at 50 yds was getting 2-3 moa half assed offhand.

Pretty sure it would have shot better off the bench
50 for initial zero, 4" "groups" 😕

gonna check to make sure bbl nit is tight and crown is good when I get home...hoping I dont have a lemon
Mine's definitely shooting better than that. I am just running a carry handle for the rear sight. Had to raise up the front sight a lot more than I thought I would to get it on. Was shooting 55gr. fmj.
BBL should be set up for 55s, that's what the Tiawanese military uses. Wolf gold is manufactured in tiawan to their military specs.

Next time I go to the range, I will try to remember to bring it and take a picture or measure my group size.

Check out T91 tactical if you want to make it more of a military clone.
Well...at the range right now....
Swapped prism 2.5x out for a vortex sparc to eliminate the optic, ran 4 different loads...
2 factory fiochi vmax, 50 and 40 grain, then same 55gr bulk I was using then some round nose sierras I had....all 5" groups at 50 yards....threw same ammo from my savage 111 at 100, all held 1" groups.
I think I have a lemon 😕
That sucks, mine isn't under 1" at 100 or anything spectacular, but it's definitely better than 5" at 50.
Can you send it back?
I'm disappointed to say the least....I'll have to check to see if there is any warranty, bought it almost a year ago, just hadnt had the chance to take it out.
are you getting keyholing? Try some different ranges and see if you are. Maybe just a bad barrel.
Do they use a normal AR barrel? I haven't looked that closely. Since they have a proprietary gas block and barrel nut I'm betting you would have to get one from T91tactical.com, if they are in stock.

Of course if he has to do that then might as well build a Taiwanese Military rifle clone...:dustin:
They are different from a standard AR barrel, not sure exactly how, but I know t91 tactical sells different gas blocks for the wolf barrels and clones built with ar barrels.
Well bump with some good news....

Ran some ladder tests with a couple different powders and some 62gr hornady HPs. Found three loads that were 3/4" @ 50yds ( so 1.5 moa )...I can live with that.
Kinda bummed its so fucking picky, but happy I was able to solve the problem.
I was meaning with the wolf a1 upper. Would like to try some with mine,but haven't had any time to make it out shooting and picked up a lovely case of pneumonia last week.
Decided that the carry handle wasn't doing it for me and put a romeo7 on it.
Just need to get it out to the range.
Are all the t91 uppers slick side?
Yes. Guess the Koreans decided that forward assist was unnecessary. I've never needed it personally but never been in a combat situation to judge their decision.

Makes it slightly lighter in the upper but the piston related parts change the balance forward just a bit.
I’m no engineer or anything but from a mechanical point of view, a forward assist looks just about useless to me.

Anyone have an accurate weight for the complete upper?
Looked at mine in the safe yesterday 😃

I think they are a great for the money, teo of my buddies are running them also...think my issue was just with my bull reloaded ammo...
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