Hybrid T91 Front Sight

Thu Jun 29, 2017 8:20 pm

I have 2 genuine T91 FSB but as stated in other places, the barrle hole is too small for US .750 barrel. There is not enough wall to enlarge it either. However, it dawn to me that I can still utilize the take down button and hence the front swivel. Here you go:

12.jpg

13.jpg

e292644 · Fri Jun 30, 2017 8:50 am

Fri Jun 30, 2017 5:39 pm

Good idea. I spoke with a gentleman the other day about barrels and if we have the profile he can turn out barrels with the correct profile and port drilling. It won't be a cheap solution but would allow for the correct FSB to be used.

e292644 · Sat Jul 01, 2017 4:48 am

In two or three weeks. There's chance I may get several modified FSB samples able to fit 0.625" and 0.750" barrel.
I will update here once I received it.

Mon Jul 03, 2017 10:52 am

I also confirm with 0.625source that the area under the FSB on the mil-spec T91 is 0.625. So as long as the barrel size is smaller than that in front of the FSB area, it's GTG. Maybe somebody can even turn the existing barrel to match that?

Mon Jul 03, 2017 1:10 pm

Having a barrel turned isn't an uncommon task, ADCO could probably do it. FYI the AR pencil thin barrels have a diameter of .625 under the gas block which tapers to .550 towards the muzzle end.

Does anyone have a pic of a barrel & extension out of the upper so we can do a visual comparison?

Thu Jul 06, 2017 1:35 pm

This is what the barrels look like after being taken off of the receiver.

Thu Jul 06, 2017 4:33 pm

I'd be willing to bet an A1 mid length profile barrel with extension would work. This is the diagram for a pencil profile carbine one.

A1.jpg

e292644 · Thu Jul 06, 2017 5:07 pm

Agreed, pencil profile barrel with modified front gas block should work.

Thu Jul 06, 2017 7:04 pm

Well....

Top one is a DD mid-length 16" lightweight barrel for comparison purposes.

This is the position of the gas port/gas block shoulder when the barrel extensions are lined up:

Thu Jul 06, 2017 9:37 pm

Welp an A1 over the counter barrel isn't going to work, gas port is in the wrong location (towards the rear of the profile vs middle which is where it needs to be). BCM will sell an undrilled barrel (you have to call and specify) with the correct diameter but it'll run around $300 and then you'll have to have the gas port drilled. IMHO it's cheaper to get the Wolf barrel turned down.

e292644 · Fri Jul 07, 2017 6:15 am

Gas block landing area to barrel extension length are different, maybe we can get the push rod length extended. Can you let us know the measurement on both?

Mon Jul 10, 2017 10:18 am

I'm going to try this tonight and try to replicate your results, great hack, tho, has me wondering whether this was intended from design?
...
Thx,
-blue

Sat Aug 25, 2018 2:53 pm

darkest2000 wrote: ↑Thu Jul 06, 2017 7:04 pm Well....

Top one is a DD mid-length 16" lightweight barrel for comparison purposes.

This is the position of the gas port/gas block shoulder when the barrel extensions are lined up:

Would you please re-post these two pictures?
I am going to build a mil-spec T91 FSB with regular AR-15 barrel.
Many thanks!

Sun Aug 26, 2018 8:26 pm

I think it would be difficult to use a regular AR15 barrel due to the location of the FSB shoulder...unless you're going to use a barrel blank or a heavy barrel and re-contour the whole thing.

Here's an T91 upper that I built by turning down a wolf A1 barrel to the correct 15mm profile with a original military FSB fitted.