It’s unfortunate that when tabletop volumes or works of fine journalism cover the weapons used in a particular time or place, they always seem to paint a nice neat picture: M16A1s squared off against AK-47s in Vietnam, Lee-Enfields against Mausers in the Boer Wars, and of course Martini-Henrys against spears in Isandlwana. A more clear picture of history accounts for older weapons used along with the state-of-the-art: Berdan rifles were pressed into service in World War II, Lee-Enfield rifles continue to be fired in anger in Afghanistan, and Mongol riders still use snaphaunce flintlocks.
It’s then surprising, but not shocking, to see in use by Burmese police forces, alongside Colt 603 AR-15s, a Greener Police Gun… Or even two or three:

To further add to the eclectic mix, some Burmese police officers are using a wood-stocked standalone grenade launcher I cannot identify.

The Greener Police Gun was developed after World War I as a police arm utilizing proprietary ammunition, so that captured guns could not be used by less savory elements against the police themselves! The weapon is based on the Martini-Henry, and the Mark III version fires a proprietary brass-cased bottlenecked shotgun cartridge (approx. 14 gauge). The base of that round is not too far removed from 12 gauge, so it is possible that the Burmese have reamed out the guns to accommodate the much more common 12 gauge ammunition, instead of the now long-obsolete Greener round. Interestingly, the Greener was also designed to make a sturdy club for disciplining unruly citizens, should the need arise.