Here's an SP1 rifle with the later style of birdcage flash hider.
The M16 would turn out to have a couple of complications when adopted and issued during the Vietnam War, and by complications I would mean enforced user error.
Mainly, after the rifle was adopted, the loading of the 5.56mm cartridge was changed, using a different powder (to save money), this powder would actually up pressure by a good bit, which would increase muzzle velocity, but also increased the cyclic rate of the action by about 200rpm more than normal, which would lead to a number of catastrophic problems.
With the action running too fast, issues you could look forward to happening would be the hammer following the bolt into battery, meaning it wasn't cocked after the last shot and pulling the trigger did nothing.
The bolt could slam into battery before it had a chance to pick up a cartridge from the magazine, leaving you with nothing at all in the chamber, meaning pulling the trigger would do nothing.
What else could happen would be that the action would open up slightly too early, which could lead to delightful things like the extractor slipping off the rim of the cartridge and not pulling the case out of the chamber, then trying to feed the next live cartridge into the ass of the spent casing, or worse, it doesn't slip off and instead tears off a chunk of the casing (which won't come out because pressure in the chamber is still too high), which still leaves the rest of the case in there and makes it bothersome to try to get it out.
Worst is that the extractor claw gets a good solid grasp on the rim of the cartridge, and extracts only the ass of the cartridge (as in it tears of the entire head of the fucking case), leaving most of it still in the chamber, then spitting out the stump of what was once a 5.56mm casing. Now you're REALLY up shit creek because you need a special armorer's tool to get that shit out, and nothing is gonna happen when you pull the trigger until you do.