An empty shell of a gift (Or, Second World War Trench art and Identifying WW2 cartridges)

You should never begin a piece with a question. Since Ive already begun with a statement, however, I can pose one now:

When is it acceptable to put a lighted cigarette near an anti-tank shell? Answer:

Trench Art: An ashtray made from a 1941 2 Pdr No1 Mk II Anti-tank shell



When said shell has lovingly been fashioned into an ashtray by bored RAF in a desert... Why RAF in a desert? Well get to that later. For now, let's take a look at an item whose tyoe is taking the collecting world by storm. Trench Art has held a fascination for years. Its an odd combination of a personal, lovingly crafted item and memorabilia from a vicious historic conflict. Which conflict, of course, affects the value and determines the age. But it does not seem to greatly affect the type of item. An ashtray could just as well come from the first or second world wars or from very recently in afghanistan. Check out some of the Afghan stuff here:
http://bfbs.com/news/afghanistan/trench-art-day-life-3703.html
Trench art first became prominant during the First World War, but dates back to the 19th Century. Wherever in history vast numbers of bored blokes have been sat around lots of scrap metal, tinkering has usually occured...
So, with that in mind, how do you tell the age/provenance of a piece? Sometimes youll be lucky enough to find a piece that has stayed in the family from an elderly relative or friend. These items were made mostly for personal use, or as gifts for loved ones back home. Such provenance of course increases the value. My ashtray above is worth between £15 - £25, not an awful lot. WW1 Tranch Art goes for considerably more. You can at least double the value if you know who produced it and where, and if that person is in some way famous, the item approaches the realms of the priceless. In truth, it can be very difficult to tell. The key is knowing what equipment/kit was available to armies from various periods/theatres and spotting bits of it in your item. Some stuff from WW2 has bits of German medals and nazi brooches incorporated. 
Some if the pieces we see are regimental in nature and feature the individuals capbadge, again giving us clues. Royal Engineers is perhaps not very helpful, but many corps, such as the Machine Gun Corps, were only around for specific conflicts (It was formed in 1915 for WW1 and disbanded in 1922) so anything with the twin machine guns capbadge is WW1.
Items are sometimes inscribed, which obviously can give us specific dates or the names of individuals we may be able to trace through records.
Better yet, is a mark on the bottom of all rounds called a 'headstamp' used to identify the round. It can tell you pretty much everything you need to know about the original item. Lets have a look at our ashtray again, this time from below:

1941 is twice stamped, most clearly in the centre, so we have WW2 straight away. 1941 saw conflict in a number of places, Burma, North Africa, Crete, but lets not get ahead of ourselves. Top we have written 2PrNo1MKII. 2 Pounder is the weight of the shell, so an anti-tank shell is our best guess, fired from a 40mm gun. Others are better qualified to take it from here, but i believe the army used the 2 Pdr No 2 during the war, so this may be a naval shell or from an aircraft mounted weapon. The RAF hurricane's, the Tank Busters, used this kind of ammunition but not until 1942, and later in the Far East, so this is probably a naval gun (he waits for the corrective comments to flood in!) im not sure, but all the information is there for you. More on headstamps at a later post... For now my nan has a new old ashtray as a birthday gift! She served on an operational RAF station during WW2, so I hope Im wrong about it being naval...