11.5” Colt FBI Barrel Ejection

[Clint]

~2:00 ejection with that setup is not too surprising.

Tube and port sizes are not exactly the same as barrel ports, so filling out the application info on the order page is best.

An 065 equivalent should work nicely for mixed use.

I was just looking at those. But do you think a .069 port would through xm193 brass forward at 1-2 o’clock...with an H2 buffer? I hope it’s actually .069 and not bigger. What size tube/port size would you recommend then? I though .069 was small and specd that way because the intent was to use it mixed

[OldState]

Thanks. Does that application mean someone will suggest a size? I filled it out but didn’t see where there would be communication.

[Clint]

The application info input is part of the ordering process.

If you select "BRT recommended size", we make the sizing determination during order fulfillment for your customized requirements.

Alternatively, you can send those same parameters to us at info@brt (spelled out) to get an answer back via email.

Thanks. Does that application mean someone will suggest a size? I filled it out but didn’t see where there would be communication.

[MQ105]

For what it's worth, my Colt heavy 11.5" measured .069". A 1.75mm drill bit (.0689") fit very snug. Shouldn't matter, but mine doesn't have a FSB.
I put in a .0625 homemade port and run it with a M4SDII, A5H2 buffer, and Tubbs flat rifle (AR-10) spring.

[OldState]

For what it's worth, my Colt heavy 11.5" measured .069". A 1.75mm drill bit (.0689") fit very snug. Shouldn't matter, but mine doesn't have a FSB.
I put in a .0625 homemade port and run it with a M4SDII, A5H2 buffer, and Tubbs flat rifle (AR-10) spring.

I didn’t even think to test it with a drill bit. Now I’m not sure I feel like stripping it down to test. Curiosity may get me though....plus I’m not sure I want to try a “remedy” without determining the actual GP size.

[MQ105]

Correct gas port size is key to optimal functioning in an AR, in my opinion. You would need to disassemble to install a port anyway. Personally, I like to know exactly what I have...
I have a bunch of drill bits in metric, #, inch, and letter sizes that cover .050-.095" in small increments. I decided to use bits instead of pin gauges because I make my own inserts and use the bits for both measuring and drilling.

[Clint]

With the tube or port solutions, the exact current size doesn't matter much.

The smaller secondary port takes over and drops the flow down to what you want.

[OldState]

With the tube or port solutions, the exact current size doesn't matter much.

The smaller secondary port takes over and drops the flow down to what you want.

I understand, but if the port is .069 already adding a .069 secondary port would be pointless for example. I think I need a point of reference to understand why this thing is ejecting the way it is. If I measure and find that it’s actually.076 that would play a part in my decision.

I think your tubes will be the best solution in the end.

[everready73]

I understand, but if the port is .069 already adding a .069 secondary port would be pointless for example. I think I need a point of reference to understand why this thing is ejecting the way it is. If I measure and find that it’s actually.076 that would play a part in my decision.

I think your tubes will be the best solution in the end.

Appreciate an update if you do measure the port. I was going to order on of the barrels from AU, but having reservations

[Clint]

Anyone looking for a dedicated suppressed or 50/50 barrel should check out our 11.5" OPTIMUM CQB-S