The National Civil War Centre is urging metal detectorists to play an even bigger role in protecting the region's priceless heritage.

Museum chiefs say that without the efforts of amateur detectorist many of the display cabinets in the nation's museums – including the new £5.4m centre in Newark - would be bare.

But there are fears that some historic finds are being discarded and lost for ever.

These include musket balls and to a lesser extent cannon balls from the British civil war period which may not have a significant financial value as artefacts, but which could be melted down for their value in lead. These objects also have a story to tell and help piece together the course of battles and sieges.

Glyn Hughes, Collections Team Leader, explained:

"Where these objects are discovered and in what concentration helps provide a window on the past. But when they are destroyed they are gone permanently and take their story with them. There is plenty of ordinance out there waiting to be discovered - Newark endured three sieges and was surrounded by up to 16,000 Parliamentarian and Scots troops for six months. We have a brilliant relationship with many detectorists, but we want to appeal to a very small minority who may occasionally weigh in musket balls for their lead value to come to us first. Usually they do so because they lack an understanding of what we can gain by preserving such items."

Just 10 years ago Newark museum had just half a dozen musket balls in its collection – now it has amassed hundreds by working with detectorists. Maurice Richardson, from Newark, who discovered an Iron Age golden necklace in 2005, which is now on display at the National Civil War Centre, added:

"We come across a lot of lead musket balls and occasionally cannon balls. They have survived for over 370 years and are part of the fabric of our history. For the vast majority of detectorists what gets them out of bed in the morning is the thrill of discovery and helping bring to objects to light and preserving them."

Detectorists and the public are being invited to bring along their finds for recording and identification at an antiquities roadshow at the National Civil War Centre on Saturday 18 July from 10am to 1pm. Admission is free to those bringing along objects.

Then from 1pm to 3pm there will be chance to handle objects in the museum collection. Normal admission is £7 adults, £6 concessions and £3 children. Entry is free for season tickets holders and half price for English Heritage members. The centre is open daily 10am to 5pm.