An interesting type of error is the broadstrike. Broadstrikes are coins that have been struck while the coin planchet is totally or partially unconstrained by the collar. The collar is the third major part of the coining process, and normally the blank planchet sits within the collar and when struck the metal of the planchet expands until constrained by the collar. Often this constraint is used to impart a design on the edge of the coin such as reeding.
When the planchet is free to move beyond the normal amount allowed by the coining collar the result is a ‘broadstrike’. Typically broadstrikes are thinner than a normal coin and quite a bit wider and not usually round. In addition elements of the design are usually very weakly struck or missing altogether.
Availability of pre-decimal broadstrikes depends largely on date. Early pre-decimals are very difficult to find broadstruck in any condition. George VI and Elizabeth II pre decimal coins are not too difficult to find, with the copper coins more common than the silver, and the lower denomination silver coins (3d and 6d) more common than the shilling and florin. This is likely to be the case simply because of the much larger mintages of the lower value coins. Some years are more commonly found (such as 1948y half pennies) as broadstrikes, and other years less so (such as 1951PL copper coins), Silver coins struck in the USA during World War II and 1960-64 silver can also be found reasonably easily as broadstrikes.
Those looking for broadstruck Australian decimal coins need to look no further than the 5 cent coin, with most dates from 2000 to 2005 available at most times on eBay. Clearly those years were not good for the RAM! One and two cent coins can be found broadstruck too, especially earlier dates (pre 1970) and 10 cent coins from the early 2000’s can sometimes be found as broadstrikes. Larger denomination coins (20 cent, 50 cent, $1 and $2) are rare as broadstrike errors with the exception being the 2005 dollar coin (see above). It appears that there was a problem with one die run on the 2005 mob of roos dollar and a number of broadstrike errors were the result. They can be found from time to time on dealer’s websites and eBay.
As normal when collecting any coin you should purchase errors in the best grade that you can afford. Australian Errors are not typically graded when sold but the same sorts of standards used to grade normal circulation coins can be applied. Broadstruck coins in UNC (uncirculated) or even EF (extremely fine) condition are spectacular coins indeed!