Original drill ammunition was made from bullets with a hollow base.. a short length of dowelling was then fitted between the bullet and the base of the case to prevent the bullet being pushed back into the case. I don't know if these bullets were specially made or they were just taken off the line before the bases were finally formed. I suspect the former!
When I make up drill rounds, I usually put in a length of dowel to achieve the same effect. I also tend to drill a small hole in the side of the case to prove it is free from explosive, particularly if there is a chance that the round may fall into the hands of the public.
There is no legal requirement to do anything with drill ammunition in UK, despite what "laws" the Police may dream up! Common sense however dictates that the more you can do to prove a drill round contains no active components, the shorter the argument is likely to be. Having been in the business of getting rid of stray ammunition, can I make the following points:
1. If in doubt, the Police will tend to seize first and ask questions later.
2. EOD have no compunction about blowing stuff in situ if they feel like it.. again never make anything that looks like it is live, unless you want to have a long and embarrassing discussion with your insurance company!
3. All recovered military ammunition and components thereof technically remain crown property unless you can produce certified documentation to prove that it has been sold out of service! This also includes any enemy ammunition that is found on UK land. Just because you unearth a 500KG Lufwaffe bomb in your cabbage patch does not mean you can keep it! ANY ammunition or components which have explosive fillings, regardless of where they came from, are technically Sect 1 or V forbidden items unless you have proper certification that they are "free from explosive". In practice this is often ignored/forgotten about, however do not push your chances...!