Three masked men threatened a shopkeeper with what appeared to be a small handgun before making off with cash, cigarettes and bottles of booze.
Sussex Police are investigating the robbery which took place at the Happy Shopper convenience store on the A259 on Saturday.
The terrifying ordeal took place at around 9pm on December 21 just as the shop was closing.
The robbers wore hoods over their heads and scarves or handkerchiefs over their faces as they entered the shop and demanded cash.
One man pointed what seemed to be a small handgun at the proprietor. Two others carried metal bars.
After stealing cash, cigarettes and drink the men drove off in a medium-sized white van which had been parked outside.
They headed west along the A259 in the direction of Little Common and Eastbourne.
Since the robbery, in which the shopkeeper was manually struck on the arm but not seriously hurt, police have carried out house-to-house enquiries in the area.
Detective Inspector Gavin Patch, of Sussex Police CID, said: “We now need to know if anyone saw what happened or recalls seeing the three men or their white van, either approaching the shop or driving off after the robbery.
“Anyone who may be able to help is asked to phone Sussex Police on 101 or email firstname.lastname@example.org, quoting serial 1502 of 22/12. Alternatively, I’d ask them to contact the independent charity Crimestoppers, which they can do free and anonymously on 0800 555 111.”