Whitcoulls has quietly pulled a book from its website that teaches readers how to alter semi-automatic assault rifles into fully automatic weapons.

The book entitled Full Auto Volume One was for sale on the website yesterday morning for $24.95.

The same book is available for $11.95 on Amazon after being discounted from $13.03.

But after the Herald sought comment from Whitcoulls about the book yesterday, it was removed from the company's website.

The decision comes just days after Whitcoulls sent an email to a customer saying it had stopped selling Canadian psychologist Jordan Peterson's 12 Rules for Life "in light of some extremely disturbing material being circulated prior, during and after the Christchurch attacks".

Prime Minister Jacinda Ardern banned semi-automatic rifles days after an Australian-born man allegedly used semi-automatic weapons to kill 50 people at two mosques in Christchurch on March 15.

Ardern announced an amnesty period and declared a gun buyback scheme would be developed which would cost the Government between $100 million and $200 million.

According to the book's introduction, it aims to explain how to convert a semi-automatic AR-15 assault rifle into a fully automatic weapon. That is one of the weapons which the accused gunman used.

"While the author does not wish to get into a lengthy discussion on the pros and cons of various gun law, it should be pointed out that had our forefathers not broken a few laws we would still be an English Colony!

"Also you cannot be arrested for possessing knowledge.

"It is in this context that this information is presented."

Whitcoulls has not yet responded to requests for comment but has taken the book off the website.

It is unclear if the book is still stocked on store shelves.

However, the Jordan Peterson book is still listed for sale on the Whitcoulls website.

Simon Mount, an Auckland Queen's Counsel who advised an inquiry on gun laws by Sir Thomas Thorp in 1997, said one of the reasons Thorp recommended banning military-style semi-automatics was the fact that many of them could be converted to fully automatic fire.

"Many of these firearms were originally designed to be fired in fully automatic mode and the civilian models are essentially the same gun modified to semi-automatic status," he said.

"A fully automatic firearm is classed as a restricted weapon, which must be rendered inoperable. In most cases, converting a semi-automatic firearm to a fully automatic weapon would be unlawful in New Zealand.

"While the safest way to avoid this is to ban military-style semi-automatics, there is at a minimum an obvious ethical question that any bookseller would need to consider before making this information available to members of the public.

"In some cases, it could also be illegal for a person, including a bookseller, to make that information available - for example if it was known that the information would be used to convert a firearm unlawfully."

NZ National Rifle Association president Malcolm Dodson said information about converting semi-automatic rifles to full automatics was available online.

"Most stuff that is available online is available printed somewhere. That's all it is," he said.

He said the NZ association represented only sporting shooters using single-shot target rifles, not semi-automatics or automatics.