Q for those of you who build a mil-spec FSB T91 with .750 journal 14.5/16 barrel

Moderators: blueeyedwolf, e292644

Post Reply
User avatar
Prelude
II
Posts: 16
Joined: Tue Jun 13, 2017 2:41 pm

Wed Mar 27, 2019 1:53 pm

How accurate is your rifle?
What barrel did you use?
If a mid-length barrel is used, did you drill another gas port or used the mid-length one?
I have found the gas port I drilled on a pistol gas system barrel for my T91 build is almost on the same spot of a mid-length gas port.
Image
Thank you!


User avatar
apex
II
Posts: 5
Joined: Sun Dec 09, 2018 1:59 pm
Country: USA
Location: MD

Fri Mar 29, 2019 5:32 pm

I originally planned to do this as well and did more research than I thought was necessary, but it wasn't enough.
So, the gas port on the T91 IS in the same spot as on a standard mid-length AR gas system, but it is drilled at a 30 degree angle like an AK. Whether this will correctly line up with a perfectly drilled .750 gas block is another issue since I never got this far.
The first problem now is how you are going to get the gas block to line up with the port and go past the block shoulder, as it sits about 1/2in further back than on an AR. Well, there's 3 solutions:
1. Get a shoulderless-barrel
This is the most expensive option, as I've only been able to find two companies that produce a shoulderless .750 .223/5.56 barrel (without going custom-made):
Ballistic Advantage "Hanson"-profile barrels: https://ballisticadvantage.com/14-5-inc ... arrel.html (14.5in), https://ballisticadvantage.com/16-inch- ... arrel.html (16in)
Bravo Company "Enhanced" barrel: https://www.bravocompanyusa.com/BCM-14- ... wf-std.htm
Both of these will run you over $200 for the barrel alone. If you want to do this on a budget this is not the best option.
2. Get a low-profile shoulder barrel and widen the barrel hole on the gas block
This was my second idea. I found this cheap beater Bear Creek .223 Wylde barrel on sale at Primary Arms and went for it (hey, it's on sale again!): https://www.bearcreekarsenal.com/bca-ar ... -1-8-twist
The gas block shoulder is very thin, and simply drilling out the gas block about 1/2in in to widen it to fit over the journal seemed like a good idea. I never went though with this though, but the parkerized Wolf A1 standard flash hider fits perfectly with the barrel's parkerized finish.
3. Turn down the gas block shoulder
This is the most dangerous option as this could bend your barrel and mess it up beyond repair very easily. Unless you are/can find a competant gunsmith who has experience in this I would advise not doing this.
4. Abandon the .750 barrel and just use the .708 gas block for the Wolf A1 barrel
This is the option I ultimately ended up going with since it required the least amount of work. Pulling off the A1 gas block can be a pain but with the proper tools (which I didn't have) it's a 5-second job. I just went ahead and got a 14.5in barrel, slapped the Wolf mil-spec block on, pinned and welded the mil-spec flash hider to the barrel so it's a 16in barrel (no ATF tax stamp or """handgun""" requirement), filed the weld down, and finally cold-blued the filed weld and bare metal spots so it's not really noticeable from a distance.
21684621654.JPG
I wish ye luck my friend.
You do not have the required permissions to view the files attached to this post.
User avatar
Prelude
II
Posts: 16
Joined: Tue Jun 13, 2017 2:41 pm

Sun Mar 31, 2019 6:17 pm

Thank you for sharing your experience! Much appreciated!
I have tried Anderson's 14.5 barrel with pistol gas system for my T91 build, it functions flawlessly after maybe 30 rounds break-in. It looks nice and everything but it shoots poorly. 3.5 inches group at 50 yards with factory ammo. Slightly better with hand-loads.
I am not sure if my drilling of gas port messed up the barrel, but without a bore scope, it is hard to tell.
Now I am planning your option 3, turn a mid-length barrel to remove its shoulder and test fit with my drilled mil-spec T91 FSB. If the gas port line up fine then I will test fire it. See how it shoots...
Wish me luck!
By the way, did you have to drill another gas port for your 14.5 wolf a1 barrel after the mil-spec FSB is installed?
User avatar
apex
II
Posts: 5
Joined: Sun Dec 09, 2018 1:59 pm
Country: USA
Location: MD

Tue Apr 02, 2019 5:15 pm

Prelude wrote:
Sun Mar 31, 2019 6:17 pm
By the way, did you have to drill another gas port for your 14.5 wolf a1 barrel after the mil-spec FSB is installed?
Nope. Luckily the gas block I ordered had the port already drilled out, and it lined up perfectly with the existing hole on the Wolf barrel.

On the Anderson barrel, did you block off the previously-drilled pistol gas port and does the T91 gas block have a good seal on the barrel? Either might be causing gas to bleed off and could cause accuracy issues. Granted though, I wouldn't expect a sub-2in group at 100yrds out of an Anderson barrel.
User avatar
Prelude
II
Posts: 16
Joined: Tue Jun 13, 2017 2:41 pm

Wed Apr 03, 2019 10:17 am

apex wrote:
Tue Apr 02, 2019 5:15 pm
Prelude wrote:
Sun Mar 31, 2019 6:17 pm
By the way, did you have to drill another gas port for your 14.5 wolf a1 barrel after the mil-spec FSB is installed?
Nope. Luckily the gas block I ordered had the port already drilled out, and it lined up perfectly with the existing hole on the Wolf barrel.

On the Anderson barrel, did you block off the previously-drilled pistol gas port and does the T91 gas block have a good seal on the barrel? Either might be causing gas to bleed off and could cause accuracy issues. Granted though, I wouldn't expect a sub-2in group at 100yrds out of an Anderson barrel.
I welded a regular gas block onto the shoulder of the barrel to cover the pistol gas port.
The gas block walked with just set screws, that's why I welded it.
Image
Image
The accuracy stays the same. (with set screws or welded gas block....)

That is good to know the gas port on wolf a1 14.5 barrel will line up with mil-spec gas block!

The mid-length barrel showed on the fist post is on the way to have its shoulder trimmed.
Will report back after the installation and test fire...
Post Reply