You have a very desirable weapon there with the 1955 made No4Mk2 infantry919. This is my opinion and mine alone.

As The Armourer has shown you, the accuracy will be outstanding, right up to moment the barrel has lost all of its integrity. 

You might have spent a good sum of money on the ammunition but, you would be better off displaying the ammunition still on the belts as britrifles suggested. 

Was your rifle still mummy wrapped when you purchased it?

If not, ask yourself the question. How many rounds of ammunition have been through it from its previous caretakers until you acquired it?

The given or projected barrel life is ten thousand rounds for the MG but is also a standard for the No4 rifles. 500 rounds seem like such a small number is comparison to 10,000 does it not? That leaves you with 9500 rounds of whatever standardized 303B ammunition you have chosen, if in fact the rifle has never been used until you came into possession of it. Here the rub.

One of those previous caretakers could have been a competitive rifleman with the CMP as an example.  That person could very easily go through 200 rounds in one week of shooting.  If he or she managed 200 round a week for one year, it has just had 10,400 rounds through it before you even had a chance to fire it. If the above scenario was true then, your rifle is already over the suggested barrel life and would be deemed unsafe from an armourers or gunsmith perspective.  If on the otherhand your rifle was unfired,(minus the initial test firing from the factory,) when you recieved it and your are a casual shooter who will maybe see a chance of getting less than 500 rounds down range in a six month period, then maybe treat yourself to one belt. Just like a good sipping whisky, keep it in moderations.