Elliot Jorgensen and Anthony Boyd were involved in the armed raid at the prestigious Rox store in Edinburgh city centre in January this year.
The robbery – which lasted less than 90 seconds – saw a large haul of expensive items stolen, including diamonds and watches. None of it has been recovered to date.
Staff were threatened with a gun and an axe, with one female worker dragged across the store at gunpoint.
Jorgensen, 25, and Boyd, 26, admitted a charge of assault and robbery yesterday when they appeared at the High Court in Glasgow.
Jorgensen was previously jailed for robbery in 2007.
Judge Lord Matthews adjourned the case until next month, but said a lengthy jail-term is “obvious” when they return to the dock.
Prosecutor Andrew Brown QC told how the robbery was carefully planned and “efficiently executed”.
He explained how the two accused played “different, but vital” roles in the crime.
Jorgensen, of Salford, Greater Manchester, was involved in the raid with an unknown accomplice while Boyd, of Manchester, had a central role in its “organisation”.
Mr Brown said “reconnaissance” was also carried out on the jewellery store in George Street.
It was also discovered that Boyd had later asked another man to transport a stolen motor bike from Manchester to Edinburgh.
Jorgensen’s QC, Jim Keegan, and Boyd’s lawyer, Liam O’Donnell, tendered guilty pleas on their behalf.
A third man – Aldair Warmington, 26, – was also alleged to have been involved in the Rox store robbery, but his not guilty pleas were accepted by prosecutors.