So .065 size insert?
@allensaldi

Yes. I did it on a Geissele gas block with the BRT kit and a drill press. The tricky, and even that is not THAT tricky, is the fact that you must drill thru the existing tapped hole without damaging the threads. If you align well, it is not hard. The inserts use the same thread size as the set screw. The drill in the BRT kit is sized to minimize thread contact but still allow the hole to be tapped easily. I used TAP Magic. The tap is long enough to screw thru set screw tapped hole and into the GB hole you opened up. A word of caution, when you tap the hole for the jet, do it in steps a little at a time so that you only tap deep enough to let the jet screw in until it is just flush enough to let the barrel slide thru the GB. You are not to tap all the way thru into the gas tube hole.

Yes, it is finely tuned. BRT tries to give you the best recommendation they can for your specific combination of parts, ammo and use. My AR is not an FBI clone, in part, because it uses a 10.5" barrel and Mk4 9.5" rail. With BRT's help I use a .0635" jet with my Surefire Optimized Bolt group. I shoot suppressed and non-. It functions perfectly with any quality NATO 5.56 (55gr, 62 gr, 69 gr, 75 gr and 77 gr) or .223 (55 gr and 62 gr)ammo. Recoil and crud blowback is greatly improved. It just feels very smooth and controlled. BRT had not set up an SBR with the SF OBG before mine so it was great to see them nail it so quickly. It all functions so well that once we can get back to the range, we may try dropping the jet one more size. With the .0635" jet I have tried to find the "floor" by trying to induce non-suppressed failures by "limp-wristing" my grip and hold and technique without success. It just runs.

After I purchased my Ballistic Advantage Barrel and realized that the existing gas port in that barrel was .073", I called BRT and spoke with them.  They asked me what ammo I was going to be using and if I was using a suppressor or not.  After getting all my information, they recommended the .065" gas port insert for the Geissele gas block which would emulate a .067" or .068" actual gas port size in the barrel.   I have no idea how or why that works...maybe it can only be a .065" insert due to the fact that the gas only has to travel a very short distance thru that restriction, but I really don't know, but that's the best explanation that I've read and I can't remember where I read it. Might even be in this thread.
Anyhoo...the ammo I was going to use that I told them was "any 5.56 or .223 ammo that I can find on sale", and YES, it was going to be suppressed AND non-suppressed.

My plan was to wait until I got all the components, namely, the GAS BLOCK (which came with the rail, which was delayed by weeks) then I was going to send it all into BRT and have them install the insert into the gas port, then install the gas block onto the barrel and it was going to cost me $100 or so if I recall.  I had gotten the BA barrel for a screaming deal for $79 so I was going to be into the barrel/gas block/gas block insert/machine work, about $200 all in by the time I was done. I'm pretty good with drill presses and such but I didn't want to attempt to do the gas port insert install on my own, plus I needed the gas block installed anyway, so I was just going to let them do it.

It was then that I found the Geissele 11.5" barrel on sale for $195.50 (with BF or Christmas discount or something...) and it came with the gas block ready to install (pre-dimpled) and also came with a .068" gas port already in the barrel.  That just seemed like an easier (and even slightly cheaper) solution to me so I did that, and I have been very happy with that decision.  

I have another AR15 that has a 10.5" barrel that has a larger gas port in it and although I love it, it is "violent" to say the least when I shoot it.  Lots of recoil and LOTS of gas when running suppressed.  Even with an H3 buffer.

I was shocked and amazed at how little recoil and how little gas is produced when suppressed with this 11.5" FBI clone with that .068" gas port.  It feels more like my DD Middy. Very smooth, very fun to shoot.

As someone above mentioned, I don't think you NEED to have the insert in the gas block, but it sure smooths it out, lessens recoil, and lessens gas face when suppressed.

Anyway, sorry for the rambling, mostly what I wanted to convey was that BRT did recommened the .065" Gas Block Insert for my AR that I was building, and that was with basically any ammo, suppressed and not suppressed, with standard (milspec) components like bolt, etc. and an 11.5" carbine gassed BA barrel.  Hope that helps.

I though it was .068 & the gas port on my Colt 11.5 heavy barrel is slightly under .070
The .070 pin doesn’t fit it’s to tight so I’d say it’s .069 which at that point makes no sense to put the BRT insert in that barrel.
Colt’s lightweight 6933 11.5 barrels are .076 that could use the BRT insert.

if anyone in the DFW would like to meet up sometime, then I will bring my issue carbine so you can determine how grey it actually is...  

are you running a super 42 spring or standard?

Anyone have any more "in the wild" shots?  Never seem to come across those anymore

I’m in the Dallas area and would love to see it in person.

They are hard to make out, but it seems to be what they're using. From @FBIElPaso on Twitter. There may be more; these are from the past few days.

I am running the spring and buffer that comes with the Surefire Optimized Bolt Group.

Here’s Mine...
Still working
I’m going for fairly CC, but like most, I’ll take a few liberties for personal preference.



Colt Cage Upper
Colt BCG
Colt HRT11.5“ BBL
Geissele GCH Green(added since pics)
Geissele Gas Block
Geissele MK4 Rail Gen1
BE Meyers ASR(for my can)
Troy BUIS
Inforce WML
Colt Geenadized RE
Colt H2 buffer
SBA4
ALG ACT trigger
Hogue grip
Matrix lower is temporary until I find a better option
Added Colt A2 Restricted lower since picks

Optics.... I go back and forth between the Eotech SU231A/Tano G33 and Vortex Viper 1-4...
I am debating going with a SIG ROMEO4

This will eventually be a proper Grey clone once I find the appropriate stock. Until then.

That looks really good, I like it!

Looks good.

There's just something that looks right about an EXPS on an SBR.

Not an FBI clone (10.5" barrel) but I have the Sig Romeo4T with a vortex micro 3x. Love the combination. I also have a Romeo4M with Juliet 4x that is very nice on another SBR (Mk18-ish). The 4M can be found for less money than the 4T but the 4t's mount, spacer (lower 1/3), battery life/solar cells and clear lens caps are worth the extra expense. It also has 4 selectable reticle choices over the 4M's.

Has any one in here dimpled their barrel for a geissele gas block?

I didn’t dimple mine. I am wondering how the gas port lines up. If the block sits against the  shoulder of the barrel or if it stands off a bit from the shoulder.

Don’t want to disassemble if I don’t have to

Edit. I guess it would help mentioning I’m using a Colt hrt barrel.

A lot of people have. Unfortunately due to barrel differences, manufacturing differences etc no one will know how your setup lines up. Fortunately it’s as simple as pulling the rail and gas block. You don’t have to mess with the barrel nut or even knock out the gas tube from the block. From there take some measurements and see for yourself.

My barrel was dimpled with the proper jig and it’s right up against the shoulder.

Sorry I don’t have a better answer for you, but there really isn’t much disassembly required to find the answer you’re seeking. Happy to help if you’re in the east valley and need a hand.

Cheers!

I was hoping to avoid pulling the gas block as it’s rocksett on.
it would help to mention I have a Colt hrt barrel.

It’s reassuring that your gb lines up with the shoulder.
I understand the minor tolerance differences. Hopefully a few others will chime in and I can put my mind to rest.

Rifle fires and functions flawlessly. I just get these crazy ideas from time to time and start to fiddle with things

@DStepec thanks for the reply. Are you running an Colt hrt barrel as well

If it runs fine go with it. I did the bombproof install on mine. I have Colt 11.5 from Shark Arms.

Attached File

Did you line up gas port and dimple prior?
Is your gb on the shoulder

Do we know if MBUS Pros are clone correct now?  I swear I saw a training pic of a ODG Fed rifle with them on it and an MLOK VFG.

I did not dimple. If I remember correctly the gas hole in the GB is oversized and will allow for some margin of error, I put it on upside down and the set screw hole lines up the the gas port.I placed some reference marks on the barrel and indexed off the shoulder.

I don’t remember seeing the Magpul pros but here is the training pic that was on the BCM Facebook page

That's the one, thanks!  Looks like I got it mixed up with the Colt Federal Patrol Rifle.  I guess they would be approved.

Looks like it has the Gov CH

Yep it does, also a 6933 lightweight barrel.
Attached File

Mix of lowers is normal at many GOV agencies, old guns get rebuilt into new configuration guns.

Have you shot the new carbine qual yet ?  I like it.

Anyone have side by side pictures of semi clone/clones setups with a gen1 and gen2 green fed rail ?

Yes, a  of those guys are either prior .MIL, prior regional SWAT or both.  Not many guys spend 20 years in HRT. Or at least not 20 years as assaulters. Like .MIL SMUs it’s a hard life and most of those guys are starting 10 years later than .MIL SMU guys so..

There is a fair amount of prior .MIL and prior LE in the Bureau.

Just because you don’t hear about it on the news doesn’t mean they never get to do anything. They do much more than just hostage rescue, Something, something quiet professionals.

Hard to say for sure  but understanding is the heavy “HRT” barrels date to an era before free float rails were in service. A frame barrels with 7” quad rails. If you don’t/can’t have a free float rail a heavy barrel is another way way to avoid or minimize things like impact shifts from barricades and slings and issues like bent barrels.

If you have a solid free float rail like a G rail, you don’t necessarily need that heavy barrel anymore. Plus you are adding weight in the form enablers like lasers.

The Bureau had a POW M4 program  through mid 2000s, it went away for a few years and came back when the first free float configurations with Troy rails were adopted for issue.

All issued carbines will eventually be converted to 11.5” G rail configuration but that is a multi year process.

One benefit to the POW programs is who gets carbines varies from office to office depending on the SAC and the PFI (Primary Firearms Instructor). In some offices they push for every agent to have a long gun. In other offices if you aren’t on SWAT or a more “dynamic” squad you aren’t getting an issued carbine. If you are in one of those offices and want a carbine for duty use the POW is your only option.

Agents can have both an issued carbine and a POW carbine “on the books” as long as they keep up with the required qualifications.

Im not cool like the FBI. I'm keeping my 3rd pin in place.

Colt M16A1 lower
Colt M4 upper
Colt 11.5 FBI heavy barrel
Geissele SSF
Aimpoint T2 on DD mount
Geissele Gov CH
SF 4 prong

Nicely done

Very nice!

I am looking for a ODG MK4 fed rail. Any leads?

Generally see one pop up in the EE every few days.

You might want to post a WTB add in EE.  People with rarer stuff to sell are pretty active there.

Ran the snot out of this HRT inspired build today in the rain, hail, sleet, snow, dust, and sunshine of a MT spring.

Never missed a beat.

Attached File


* O-Light soon to be replaced with filthy, undeserved discount scout mini pro

Does anyone have any pics of ones that were issued that arent using colt uppers?

Besides heavy colt hrt 11.5" barrels, what kind of other barrels were used or issued?

Colt 6933 profile for sure and I believe Voodoo 11.5" barrels.  I don't know too much about the Voodoo barrels, I believe they were a contract run.

Foe those running scout lights, what mount are you using?

I’m not running one yet, but plan to pick up a M300C.  When I do I plan on using the factory thumbscrew mount and attaching it to the MK4 pic rail with an SR07 at the 12:00.

340C with built in mount. No extra mount needed.

I heard yall like feet  

RE: BRT inserts

What tap/thread pitch/drill bit did you use before install? I didn't order the install kit, since I've got a crap ton of bits and taps, and I figured I'd have something in the random mix that would work.  I'll measure the threads once it gets here, but figured I'd ask you DIY guys first.

What magnifier?

Vortex Micro 3X

If you don’t get a response sooner, I’ll check what size bits and tap came with my kit when I get home today.