When I first got vz58 in .223, it arrived with an effective but loud muzzle brake. I deemed it unnecessary and wanted to replace it with a flash hider. Fortunately, at least four different options are readily available.
I got two of them, a very small and light variant (above) and a larger, more effective Phanton (below).
What impressed me about these wasn’t just the good quality machining but also the ease with which I was able to swap them. Press a detent pin, spin off the muzzle device, replace with another, release pin.
Simple, effective, toll-less, provides indexing. No crush washers needed. Why aren’t more rifle designs using this method?
My guess is because the fit isn’t as tight as the crush washer method and it affects accuracy.
Most likely because the AR platform, and many others on the market today, have a protruding barrel that extends past the front sight by several inches. Since the indexing flash hider design requires a detent pin to function, it means the front sight base must be located immediately adjacent to the end of the barrel.
Two big ones:
First, as one of the Anons mentioned already, that system requires some means of holding a detent in place next to the muzzle device, which is problematic when you don’t have anything else attached to the barrel next to the muzzle.
Second, is the issue of concentricity: The system you show here would be absolutely no good for attaching a muffler.
As long as the threads were turned concentric with the bore, and the runout was reasonable there would be no problem with a suppressor. You can mount suppressors to typical AK-74 threads which are part of the front sight, not the barrel.
As Mike said, you just swap the muzzle break with the suppressor.
The surplus Sa vz 58s we have here in Europe have concentric threads and suppressors screw on with ease (and are locked by the same detente).
There are some AK-pattern guns that have less-than-concentric threads but I have yet to see such issue on Sa vz 58s.
Crush washers are much cheaper than detent pins.
Imported guns may have ATF requirements that don’t let you change the muzzle device. Some of these have threaded barrels that then get soldered. The muzzle device then requires tools (like a torch) to remove – and the threads need cleaning up.
One more reason – extra cost vs. utility.
I’d bet a dollar that almost all guns never have the muzzle device replaced.
Military users certainly don’t pull them on and off a lot, and they have armorers on staff anyway.
Detent pins are, as mentioned above, expensive and machining-heavy in comparison – and in this case they’re basically solving a non-problem for almost all users.
I suspect that if this sorta-quick-change setup was common, muzzle attachments would be a marketable item. People don’t change them due to the difficulty. When it requires tools, you can be sure it won’t happen often. I wouldn’t doubt that a fair quantity of aftermarket breaks and flashhiders are still sitting on the rifle owner’s bench/desk, acting as paperweights, for this reason.
A reason:
Detent’s require springs. Springs and heat like you get off a barrel don’t get along very well for very long.
PSL uses that system: captive spring-loaded pin to lock the compensator on.
Something I heard from an owner: if it didn’t fit tightly enough to suit, take the comp off, and carefully rotate it on sandpaper on a flat surface. Could cut just enough off to move it to a tight fit on the next detent on the comp.
Of course, he referred to the comp as a ‘dust storm generator’ and took the damn thing off, too.