Damien from FSG was kind enough to send me one of their new metric-threaded flash suppressors for the STG to try out.
I’m not a big fan of flash suppressors for civvie use (hence my Levangs) but I’m always happy to help out and maybe learn something new in the process (and this time, I did!..
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Initial examination shows what appears to be a very well designed and rugged flash suppressor, I think you’d have to take a sledge to it to get the prongs to bend (btw, while the prongs give off a nice “ping” when you tap them, they do not do this while shooting). Instructions don’t mention using a crush washer or Loctite during installation so I tried it w/o either of these to test retention (at the end of my tests it’s still on tight w/no signs of loosening). The Halon screwed on easily by hand and has convenient flats installed for moderate tightening.
Muzzle devices tested: Factory tulip, Levang compensator and the FSG Halon.
Ammo used: Winchester Q3131A, Prvi Partizan M193 & PMC Bronze.
Ambient conditions: Nearly a full moon last night, I was afraid the bright moonlight would spoil the test (once again, “it turns out not to be the case…” 
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My wonderful wife was kind enough to try getting video of the tests (sorry, they didn’t turn out well enough to post them).
Test procedure: I held the STG out in front of me at a 90 angle pointing to my left towards a tall nearby berm so I could observe the muzzle flash; VFG in my left hand, right hand on the pistol grip (like I was trying to shoot around a corner). I used 3 42rd mags loaded w/15rds each, 5rds of PMC followed by 5rds of Q3131A followed by 5rds of Prvi M193 (1 mag per muzzle device).
Results: The Levang had the brightest flash of all (not surprising since it’s a compensator) but still not bad; a softball-sized flash that was moderately bright, let’s call it a ‘10’ as a baseline for the others.
The Tulip was about an ‘8’ compared to the Levang, definitely less flash but not a huge difference IMHO.
The FSG Halon was a pleasant surprise, about 1 or 2 compared to the Levang; very little flash and that mostly in the area between the prongs. There was so little flash that on the video it looks about the same as the flash coming out of the STG’s gas port! A bonus for me (since my taclight uses AA batteries and the extra body length places the bezel closer to the muzzle device) is that there doesn’t seem to be any blast residue or damage to the bezel of my taclight.
I was impressed…
Okay, it’s an effective flash suppressor, how does it handle during rapid fire?
Ran out to the public range this morning w/all 3 bbls and about 100rds of PMC Bronze. I double-tapped small rocks at 50yds to judge muzzle rise and speed of followup shots.
Now, the STG doesn’t have much muzzle rise to begin w/and compensators like the Levang can reduce that even more but due to the the STG’s already minor muzzle rise I found it difficult to determine a significant difference between the 3 muzzle devices (although for some reason I cannot determine the HSG Halon-equipped bbl seemed like a laser beam, always hitting what I was aiming at).
Bottom line: The factory tulip does an ‘adequate’ job of flash suppression w/o exessive muzzle rise.
The Levang directs the muzzle blast forward and slightly reduces muzzle rise at the cost of slightly increased muzzle flash and linear recoil.
The FSG Halon is a much better flash suppressor than either the Tulip or Levang (& doesn’t need an adapter like the Levang) and compared to the Tulip doesn’t seem to significantly increase muzzle rise.
Tomac
The three muzzle devices tested:
Front view of the three muzzle devices, notice the slight angle to the FSG Halon’s prongs:
STG w/the Halon bbl, notice the proximity of the Halon to the bezel of my Fenix TK20 taclight:
