This is an easy and available feature within the main save menu for your feeds. The Clone menu will give you a list of all your available storefronts (including the one that the feed currently resides).
Selecting that storefront will create a copy with all the same details (please note if you are duplicating a feed to the same store you must change the feed name field at least otherwise you will get a save error).
The other issue you may encounter is the possibility that the data element that you have built a columns data from – does not exist in the storefront database that you are copying to. If this happens – the column header will still be there but the data source in the builder will be shown as ‘unlinked’ – you will need to manually re-link these to new store data.
This scenario is most likely to happen when copying between storefronts – and also where you have built a column from product metadata.