I purchased an AGB from Hurricane Butterfly and I purchased a 10.4" barrel (They weren't purchased as a matched pair...just purchased in the same time frame). The barrel gas port is 1.7mm. I took apart the AGB to measure the regulator gas ports and I took pictures. The vent was .9mm. I'm using pin gauges and I could not get a 1.0mm pin in the port. I tried a .95mm pin and that wouldn't fit. The .9mm was the next size that fit. I see a lot that list the 1.0mm vent sizes so I was a bit uneasy regarding a .9mm; never saw that listed by anyone but that's what I got. I removed the regulator and the "N" port was 1.7mm and the "S" port was 1.2mm. I also measured each pin, while in the respective port, with a Mitutoyo 500-196-30 AOS Absolute Caliper 0-6" for verification and measurement.
There is a dimple on the AGB body (see picture); I don't know what that means but ToyCop said that it could be a 10.4" AGB. HB listed it as a 14.5/16 AGB.
I also bought a Brownells 416 parts kit and I'll provide the measurements for that next. It's a non adjustable vented gas block and I don't know what the donor barrel was; I'm assuming 14.5/16.
Last edited by Chesapeak610; 09-29-2019 at 08:48 PM.
I recently got a dimpled AGB from RKS and it doesn't have the sling loops. The gas port looks tiny so I'm assuming its for a 10" barrel since they don't list it on their page.
I just re-measured to verify that "N" is 1.7mm and not 1.55mm and it is, without a doubt, 1.7mm at the "N" port (V=.9mm, N=1.7mm, S=1.2mm). The AGB that you referenced looks identical to mine, dimple and all. I still don't know what "officially" is the corresponding HK barrel size that it supports, but that's what this beast is.
I used it with the HB 10.4" barrel on the BRN-4 lower with the HK416 Parts, set to "N", and it was fully cycling but it wasn't triggering the next round (full extraction, loading next round, pull trigger, no bang). I used a Go-No-Go gauge to verify barrel fit and it was REAL tight on the Go gauge, like it would barely go in to battery. I'm hoping that this is a barrel extension break-in issue and that I need to put some more rounds through it. I used the same lower with an MR556 upper and it worked flawlessly, so the lower should be considered solid. I'm a NOOB when it comes to building these things and am leveraging the expertise/experience of the members of this forum and others to learn quickly...it's mostly working.
So, given the calculus that IT, and others, have provided, would this AGB work with a 10,4" barrel that has a 1.7mm gas port? Anyone?
Last edited by Chesapeak610; 09-30-2019 at 12:59 AM.
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