The shot heard around the world in 1963, a bullet from an assassin's weapon that ended the life of U.S. President John F. Kennedy, is still remembered on the annually produced half dollar struck in his honor.

As far as collectors are concerned, the shot cut short not only the life of a U.S. president, but also the 15-year-old series of Franklin half dollars introduced in 1948. By law, the designs of circulating coins are not supposed to change in less than 25 years without congressional approval. Emotions ran high and Kennedy's effigy quickly replaced that of Franklin's on the obverse of the half dollar beginning in 1964 by an act of Congress.

The prototype for the obverse and reverse of the Kennedy half dollar was the inaugural medal. The half dollar obverse design is the work of U.S. Mint Chief Sculptor-Engraver Gilroy Roberts. The reverse is an interpretation of the Great Seal of the President by Sculptor-Engraver Frank Gasparro.

The 1964 Kennedy half dollar was eagerly sought by souvenir hunters, collectors and those nostalgic of the "Kennedy era." The coins were hoarded by speculators despite a mintage exceeding 273 million from the Philadelphia Mint and an additional 156 million from the Denver Mint, compared to just more than 89 million half dollar coins from both Mints combined a year earlier when Franklin's portrait was used.

Demand and an effort to place coins into circulation were primary reasons for the more than 429 million 1964 and 1964-D Kennedy half dollars. Production dropped dramatically, to about 65.8 million, in 1965.

Another situation, however, brought even more interest to the 1964 issue. In 1964 the coins were struck of .900 fine silver. This precious metal content was decreased to .400 fine in 1965. The .400 fine silver continued through 1970. All circulation-strike Kennedy half dollars since 1971 have been struck of copper-nickel composition.

All other circulating U.S. coins previously struck in silver were changed to copper-nickel composition beginning in 1965. The rising price of silver bullion was the later catalyst for the "great silver melt" of the late 1970s through March 27, 1980, when the price of silver collapsed.

Silver 1964 Kennedy half dollars are still typically priced based on the spot price of silver.

Despite the fact there are "key date" Kennedy half dollars based on mintage figures, no one knows for certain just how many coins and of what dates and Mint marks were destroyed by melting during the tumultuous 1970s.

The Bicentennial reverse depicting Independence Hall is by Seth G. Huntington, whose design was chosen in a design contest.

The 1776-1976 Bicentennial coin issue is unique in U.S. numismatic history. It is the only circulation issue (quarter dollars, half dollars and dollars) with two dates appearing together. It is one of the few times coins have been struck in another year other than that appearing on the coin (1975 and 1976 coins are dated 1776-1976).

As with the 1964 Kennedy half dollar, the Bicentennial half dollar has been commonly hoarded. Many noncollectors believe these coins may someday become very valuable.

Even a type set of Kennedy half dollars is of interest. A circulation strike type set would include a .900 fine silver coin of 1964, .400 fine silver coin of 1965 to 1970, Bicentennial reverse coin of 1776-1976 and a copper-nickel clad composition coin of 1971 to 1974 and 1977 to date. An Uncirculated type coin collector might also want to consider a 1971 to 1977 Philadelphia Mint coin without Mint mark and a coin from 1980 to date with the P Mint mark for the Philadelphia Mint.

The suggested set excludes all Proof coins, varieties and errors. The key dates to the series, according to mintage figures, are 1970-D, 1987-P and 1987-D coins. Each of these dates was only available in Souvenir Mint sets. Each of the 1987 coins was also available in Uncirculated Souvenir sets sold over the counter at the Denver and Philadelphia Mints. None of these three dates were officially issued for circulation. Since 2002, the Kennedy half dollar has not been struck for circulation. Circulation-quality Kennedy halves have been struck only for collectors and sold as numismatic products in rolls and bags.

Collectors seek a number of varieties, errors and other rarities in the Kennedy series. Among these are off-metal strikes between 1964 and 1970 when the coins were still made with silver. As an example, 1965 Kennedy half dollars are known struck in .900 fine silver. There are doubled die coins, coins with repunched Mint marks of varying clarity, dates struck in Proof only, coins without the designer's initials (probably due to overpolished dies) and die varieties.

There was some speculation during 1976 among collectors whether the presidential seal reverse would be resumed beginning in 1977. It was. Kennedy half dollars of every date have also been struck in Proof. During the Bicentennial coinage Proofs were struck in copper-nickel clad as well as in .400 fine silver.

Beginning in 1992, the Kennedy half dollar has been struck in 90 percent silver and offered in a special silver Proof set for the collector market. In 1998 the silver version was struck in a Matte Finish. Since 2005 a Satin Finish version has been produced bearing both the P and D Mint marks for Uncirculated Mint sets.

The half dollar denomination is not used as often in commerce as other denominations. This has periodically brought about discussions of possibly abolishing the denomination.