Almost never a collar. That is a modern invention. Flans typically were cast round, then struck on round dies. This enabled to have very good coins when done properly.
Justin II. Not only is the flan poor but the celator has engraved some grey aliens. What did he know that we don't today?
I have posted before, but Byzantine coins always remind me of the movie Crazy People. In it, there was a man in the asylum obsessed with Saab 900's. When they made the advertising firm a ton of money, everyone got cars. Lots of fancy drop tops, corvettes, etc. He was despondent until a crappy, rusty Saab 900 showed up. He eagerly climbed in, and tried to start it. Uggg ugg ugg, Ugg ugg ugg. Someone pulled up and asked if there was a problem. He said, "They aren't SUPPOSED to start all of the time!". Byzantine coins are similar. They are not SUPPOSED to be round, well struck, recognizable, etc ALL of the time! Truly a series where you need to do your reading, understand what they were trying to accomplish, read about the struggles they were going through at the time, and love them for their history anyway!
Good point @medoraman - I do know that Justin II had a mental collapse (probably schizophrenia or something) in response to all of the challenges he was facing to the point where he became incapable of performing his duties as head of state. He could not reconcile the Monophysite crisis and deter the Persian threat. There was also an economic crisis following Justinian's heavy level of expenditures. So ragged flans, not much of a problem in the overall scheme of things.
I guess I am thinking of these coins too much in a modern lens - where any planchet that isn't 100% perfect becomes a potentially-valuable error and is truly a rare occurrence. Back then, I doubt people would have really cared too much about the actual shape of their coin, and were more concerned about how much bread they could buy with this particular chunk of metal.
So far I think this one is the most uncharacteristically bad flan; most Hadrianic coins are rather round and with good edges. The other coins posted are mostly from eras where "perfect" coins were rather the exception than the rule; one can't expect a Byzantine coin to be round while one would certainly expect a Hadrian to be.
For some reason, flan splits that produced these ragged edges were actually not that uncommon during certain periods in Hadrian's and A-Pi's reigns. It's true they're much better for the most part, though. Here's a Hadrian with an imperfect edge showing where the blank was inexpertly broken off its casting sprue.
This should be round, instead it is an interesting oval ., Reminds me of the flat coins you get at a coin fair , when you get the squashed penny.
This one (from @tenbobbit) is really rather quite excellent for a Claudius, but I love the little tumor on the side.
Among my Byzantines, most notable for this thread is this Heraclius. The shape is not so bad but those points are as sharp as a chain saw. I bought it by mail and it arrived having cut its way out of the flip and had one corner sticking out of the envelope. I agree with the above mention of some Antoninus Pius denarii being regularly ragged. This is from his first year. Another raggedy period occurred at Rome in the middle of Septimius Severus' reign. My ratty Tetricus is a bit unusual since the coin appears to be an official mint product rather than a barbarous radiate.
And here's an official Tetricus on a horrendous flan. Too bad, since it's otherwise in superb shape! Although like many others have said, these abnormal flan types are rather endearing, and I have grown to like these for what they are.
I think this is probably my wackiest flan: Theodosius III of Adramytium (715-717), follis, Syracuse Picking up on some of the themes from up-thread: Overstrike on a cut flan: Rashidun Caliphate c. 640s-650s, Album 3508X A box cutter (ouch, sharp!): Justinian I decanummium, Antioch Stacked flans: This is only a double. @TIF, I didn't know you had a triple... wow!! ^^This coin is hysterical, I love it! Here's one of my Gallienus Kevin specials: I suppose this coin doesn't really count...
Not exactly round: Tiberius II Constantine AD 574-582 and Anastasia. Byzantine Æ half-follis, 5.02 g, 20.4 mm, 7 h. Thessalonica, AD 579. Obv: dmTibCONS TANTPPAV, Nimbate Tiberius and Anastasia seated facing on double throne; he holds globus cruciger, she a scepter. Rev: Large K; above, cross; to left, A/N/N/O; to right, regnal indicator V (=5); beneath, TЄS. Refs: Berk 398; DOC 23; SB 439; MIBE 65.