The loops were for Ballasite Blank Cartridges. Used on SMLE Rifles with the Cup discharger for No:36 Grenades.
These Blanks were painted BLACK for 3/4 of their length externally.

If you find any of these 'Blanks' NEVER, EVER be tempted to fire them in a Rifle/ LMG fitted with a Blank Firing attachment.
They WILL damage the Barrel/ Weapon & YOU!!!!! The pressure generated from these cartridges is absolutely enormous!!!