|Type of Transaction||Reportability|
|Cash transactions||In general, only reportable if paying cash (such as $20 bills) or sometimes cashier's checks and the like, but only if more than $10K (in a single transaction, or related transactions).|
|Buying Gold/Silver/Platinum/Palladium||If you buy precious metals (specifically, gold, silver, platinum or palladium), there are no reporting requirements for the dealer (except if you pay in cash; see above). You could, in theory, buy $1 billion of silver and whoever sells it to you would not need to report it.|
|Selling Gold/Silver/Platinum/Palladium||If you sell precious metals (specifically, gold, silver, platinum or palladium) to a dealer, they may be required to fill out a 1099-B form. They are required to fill out the form if both  you sell metal in a form that has been approved by the CFTC for trading by a regulated futures contract, and  you are selling enough metal to meet the minimum required for the contract. This applies per 24-hour period, so you could sell 20 coins one day, and 20 coins 24 hours later, and might not have to report. If you sell in a manner specifically to avoid the reporting requirement, reporting is then required.|
If you buy silver (or virtually anything else) from a dealer, and pay cash (either real cash, such as $20 bills, or a cashier's check or similar anonymous source of money), and the amount is over $10,000, the dealer must report it on an IRS Form 8300. Specifically, anyone 'conducting trade or business' must file the 8300 (so if you sell to an individual, they probably would not need to file the form).
The $10,000 limit applies to either a single transaction, or series of related transactions within a 12-month period. So if you buy $8,000 of silver in cash from a dealer in the morning, and another $8,000 in the afternoon (or even 6 months later) as part of a 'related transaction', they would be required to report this on the Form 8300. But if the transactions are not related, they are treated separately. Two transactions are related if they occur with 24 hours of each other, of if the dealer knows or has reason to know that the transactions are a series of connected transactions. What that really means is anyone's guess!
As for 'related transactions', the IRS states that if you purchase different items, they are considered unrelated transactions. So if you buy $8K of Silver Eagles one week, and $8K of 90% silver the next week, it should not have to be reported. Unless, of course, the dealer thinks you did so to avoid the reporting requirements. So the reporting isn't required, but you can't avoid the requirement that way. Strange, yes.
So what is cash? True cash qualifies (currency such as $20 bills and/or coins). So do cashier's checks, bank drafts, traveler's checks or money orders -- but only if they are $10,000 or under, and either the dealer knows that you are trying to avoid the reporting requirements or you silver is considered a 'designated reporting transaction' by the Treasury (section 1.6050I-1(c)(iii)). That section refers to 408(m)(3), which mentions that some coins and bullion are considered collectibles, others are not.
If the transaction is required to be reported, the business is required to inform you by January 31 of the subsequent calendar year (as is normally the case with 1099 forms). However, they must not inform you if the form is not required, but they report anyways because they are reporting a suspicious transaction.
A dealer is required to fill out a 1099-B form and report it to the IRS, if you sell silver (or gold, platinum, or palladium) in  a form that the CFTC has approved for trading, and  is at least the minimum amount to satisfy a futures contract.
Sales during a 24-hour period must be aggregated and treated as a single sale. So selling a reportable amount in two transactions more than 24 hours apart would not normally be reportable. However, there is of course an exception that if the broker knows or has reason to know that you are trying to avoid the reporting requirements, they are then required to report it.
However, the only futures contracts currently traded appear to be:
The IRS does allow for "like kind" exchanges without being taxed at the time, such as trading 1 ounce generic rounds for 1 ounce generic bars. They do not give a lot of guidance as to exactly what is considered "like kind" in terms of precious metals (except that trading silver for gold or vice-versa is not considered a like kind exchange).
Also of note is that at least one major bullion dealer reports that "We are not aware of any reporting requirements and we do not accept cash, so we do not report sales or purchases of ANY amount."
Also note that you normally are required to report the sale of precious metals on your taxes, and pay tax on any profits (as is the case with just about anything you may happen to make a profit on). This is true whether or not the sale is reported. So if you buy a silver coin for $10 and sell it for $15, no reporting will be done, but you must pay taxes on the $5 profit.