Thank you for your response, As for fitment on the VG6 and other brand brakes....
Griffin Armament QD Blast Shield Gen II... numerous reports of these working and not working on various A2 and other "A2 Collared" muzzle devices... very much a "he said, she said" thing.
Beautifully made, ( if you are "Gunny" .. it sure is purddy ) simple straight forward locking mechanism , easy fitment on 3 of the 4 I bought. ( More on that later )
I would certainly buy more again.
So, I bought a few of these. I was very interested in the fitment on other brand muzzle devices. Nothing the matter with the GA muzzle devices, I just happen to have numerous of other brand muzzle devices already.
Installing the included collar stop is straight forward as well as shimming... and necessary if you want to keep your sanity while placing the GA over your muzzle device... no stop collar and the device will slide past the proper alignment locking position... and you will struggle to install the GA blast shield gizmo. The included shims allow for more precise tuning of collar stop fitment.
So... read the instructions !!
Next comment... the "push in place locking collar" and set stop...on the GA has to align with a wrench flats on the "A2" style muzzle devices collar... oddly, every one GA devices seemed "preferred" one wrench flat side over the other .. not a big deal.. but... and that could have been me, just getting used to them.
Proper fitment means the "spring" steel locking piece fully locks in place, ... FULLY. Some of the various brand muzzle devices were close, and I am comfortable a little careful filing would allow fitment, ( at needed spots ) if you decided to do that. Don't go crazy filing... take your time and pay attention to your work. If you can't do that, then don't bother, you may not like the results at all, and may damage the fit and lock in place properties.
What I found was..In order for these to fit and lock properly you HAVE to have squared off 90 degree edges at the "A2" style collar valley's ... rounded edges in the valley will NOT work. Sharp, properly cornered off valleys that readily allow the GA locking collar to engage, are far preferred.
( A video on line complained about this, and clearly shows a less then in spec collared area. )
Next, one of the 4 GA Blast shields has very slightly tighter internal dimensions then the other 3. So... while that specific one ( GA #1 ) would slip and lock on some of the muzzle devices ( the various brakes with slightly looser collar dimensions ), the next same brand / style muzzle device , that happens to have slightly on the + end of dimensions .. flat out, would NOT even slide into the GA #1 shield.
So IMHO, that helps solve some of the "he said, she said" vagueness concerning VG6 and other brands... tolerance stacking. Certainly on the obvious on one of the VG6 end.
No small wonder GA recommends their muzzle devices, they can control dimensional properties , assuring proper fit.
GA has zero control over other manufacturers dimensional QC.... ( See below ) and it shows.
The "tight" GA (#1) was tight fitting when sliding onto the various brand muzzle devices. Probably off by a few thousands inch. I will polish it and see if that helps fitment slightly, and an easy "fix".
GA #'s 2,3 & 4 all slid on smoothly... with various proper spec'd brakes.
Again...remember.. if your brake has "A2" collars at the shoulder end, with sharp 90 degree "valleys" at the collars... excellent chance it will fit.
But I wouldn't blame Griffin Armaments for "all" the fitment issues , especially if your brakes valleys are rounded. Seriously, the spec calls for sharp corners... but, not every other manufacturer adheres to that. ( Implied "USGI" product descriptions on cheap brakes, and , frankly, those other manufacturers don't care about GA fitment on there brand brakes....Lol
Sample of 5 BCM Mod 0's ... with all 4 GA GII Shields. .... All 4 GA's slid on , 3 of the 5 BCM's worked fine, and locked properly in place ( pretty sure they are newer ones ).. the tight GA#1 was a tighter to install, but did work on those 3. Again... I believe I could fix fitment issues on the other 2.
VG6 Epilson 5.56 and 300BK , Gamma / EX... I have a bunch of these, 2 / 300BK, 4 / Epilson 5.56, 4/ Gamma, 3/ Gamma EX... One of the each style was certainly at the + end of dimensional specs. So that means the #1 GA would not even slide on the + dimensional spec VG6's... I could force them ... but after carbon build up and heat, I'd bet they would be a PITA to get off quickly.
The GA #'s 2,3,4 all slid on and locked in place properly.
4 ea Yankee Hill Phantom... same issues with GA #1, to tight... GA #'s 2,3,4 all would fit and lock in place.
AAC Blackout.... no dice, front tangs are to fat for the GA's to slid on.
Generic A2 flash hiders.... these were literally all over the place fitment wise.... Generic means just that, no real attention paid to dimensions.. a few did work, but not enough to make me content. So if you want a A2 to work, look for those sharp 90 degree valleys.
MI 2 Chamber Muzzle device..... just tried these because I have quite a few of them, very good bang for the buck comp's... none of the GA's would slid past the front collar. I might true one up and see if it could work.
Its getting late, and I may have forgotten some input... but I hope this will help when it comes to those looking at the Griffin Armament QD blast device.
And , remember, if you want a easy 100% sure fit... get a GA brake / muzzle device to install your Gen II QD Blast Shield on. That way GA controls all the fitment tolerances.
Dimensions
OD of Blast Area: 1.5"
OD of Locking Gate Area: 1.5"
OAL 3.5" long
Weight 8.75oz excluding collar stop
I will add any accuracy / POI differences after range day with all the QD devices.
FWIW... post over here concerning the GA and other QD devices over here...
https://www.ar15.com/forums/ar-15/Various-brand-QD-Blast-Devices-/118-754582/