You do see that rather often.
It originates when someone decides it will be cute to mount their can on a lorcin or other tiny 22. Since threaded or extended barrels are in short supply for these treasures, they usually receive an inside thread and a barrel extension is added and then threaded 1/2-28 which is a standard 22 can size.
But what to do with those exposed threads when the can is dismounted? Well, a standard 5.56 AR flash hider is 1/2-28...
Full Disclosure:
I made a short barrel for my ruger charger and threaded it.... it has an AR flash hider on it when it isn't equipped with a can. 
Complete thread:
- More Cerakote horrors -
Andrew,
2013-08-22, 18:31
![[*]](themes/default/images/complete_thread.png "Open whole thread")
- JEEZ. (nm) - Boge Quinn, 2013-08-22, 19:02
- ROFL -
FOG,
2013-08-22, 19:12
- ROFL -
Lee J.,
2013-08-22, 20:03
- Ruined -
Rob Leahy,
2013-08-22, 20:19
- Ruined - Lee J., 2013-08-22, 20:23
- Just to clarify -
FOG,
2013-08-22, 21:22
- Also found a 'new' forum - FOG, 2013-08-22, 21:28
- What? No light rail? - Andrew, 2013-08-22, 21:34
- You do see that rather often. - John K., 2013-08-22, 21:36
- U.N.C.L.E. Pocket Pistol? -
Drago,
2013-08-23, 11:54
- 'Just in case' - FOG, 2013-08-23, 13:19
- ♪ Theme Song ♪ - FOG, 2013-08-23, 13:23
- ♪ Long Version ♪ -
FOG,
2013-08-23, 13:29
- ♪ Now On Playlist ♪ -
FOG,
2013-08-23, 15:50
- ♪ The Ukulele Orchestra of Great Britain - TG, TB, & TU ♪ - FOG, 2013-08-26, 23:59
- ♪ Now On Playlist ♪ -
FOG,
2013-08-23, 15:50
- U.N.C.L.E. Pocket Pistol? I need a black turtleneck sweater. - Rob Leahy, 2013-08-24, 11:40
- Muzzle brake, Rail, Two-Tone Cerakote...This one has it all! -
FOG,
2013-08-26, 01:49
- I kinda like that one! - Slow Hand, 2013-08-27, 03:59
- Ruined -
Rob Leahy,
2013-08-22, 20:19
- ROFL -
Lee J.,
2013-08-22, 20:03
- Armslist. Not surprised. -
John K.,
2013-08-22, 20:37
- I'd have to have 2 of those..... - Bud, 2013-08-23, 08:27