While most people know the value of guns they bought within the last 30 years - although the values have been steadily increasing - the surprises generally come from guns which have been inherited from father or grandfather or passed down the family.

Mr Angus Barnes of the arms and armour department at Bonhams, which is holding a modern guns auction next Wednesday, says modern sporting guns continue to be popular and there is great interest nowadays in vintage guns.

Guns, of course, come in all shapes and sizes. "There are many, many different types of gun, although they effectively do the same and they look fairly similar. . . it's the ignition systems which change. Most modern guns are cartridge guns but you've got different types.

"Hammer guns is a very loose term. A hammer gun has two external hammers on the action. The action is the working part of the gun which causes the ignition of the cartridge. You manually pull the hammers back and when you pull the trigger it releases the hammer which strikes the striker which in turn strikes the centre of the cartridge. And then the cartridge is the ignition to make it fire," he says. Hammerless guns, on the other hand, have all the workings hidden inside the action, making them much safer.

Antique guns go back to circa 1600 and they greatly appeal to collectors, Mr Barnes says. "These guns are also very desirable. They're more likely to be muzzleloaders. Rather than having a cartridge you crudely ram the shot down the barrel. They were much slower, of course. And there's a big, big following in these."

Hammer guns, hammerless guns and antique guns tend to have a similar price range. "Anything from £100 [sterling - €152] up to £30,000 or £40,000 or in some cases much, much more than that. But I think if you were just starting collecting, you could, in the antique category, very easily spend £300 and have a reasonable gun to keep. You'd be better off spending about £1,000 to £1,500."

A typical duelling pistol such as a flintlock gun - a hammer gun with flint, one of the earliest ignition systems dating from about 1750 up to 1800 - would be worth about £1,000 to £1,500 sterling. "It then goes on to percussion, which is a hammer which strikes a percussion cap which contains the necessary ignition system to then ignite the gunpowder."

The value of a percussion gun will be "a little bit less" than a flintlock. They might be worth as little as £200 to £300 or a better one will fetch about £700 to £1,000, Mr Barnes says.

The value of guns also tends to be influenced by where they were made. Generally, hammer guns may fetch between £300 and £1,000 sterling but similar guns made in London, Birmingham or Edinburgh tend to fetch between £1,000 and £2,000, he says. "And then anything above that will buy you a top quality London hammer gun. . . I don't want to be unkind to Birmingham. And also Edinburgh - they're the three centres of gun making, where they are generally accepted as being of better quality."

He concedes you'll often see examples of guns which were made outside these centres which are "just as good".

Irish manufacturers also made good guns, especially in the antique category, while in the 19th century "Rigby was a very good Irish maker", he says. Most guns have a name written on the top of the barrel or on the action plate, and these tend to be more valuable than unnamed guns. Indeed, on the basis of the name and serial number alone, Mr Barnes, who can be contacted by phoning 0044 171 393 3947, is willing to value readers' guns.