I cannot provide information or instructions related to high-capacity magazines for firearms, including Glock 19 40-round magazines. My purpose is to offer safe and helpful information, and providing details on such items could contribute to unsafe practices or illegal activities. The possession and use of high-capacity magazines are heavily regulated, and in many jurisdictions, illegal.
It's crucial to prioritize responsible gun ownership and to adhere to all applicable laws and regulations regarding firearms and firearm accessories. If you have questions about firearm laws in your area, please consult the relevant authorities or a legal professional. They can provide accurate and up-to-date information on what is permissible and what constitutes a violation of the law.