I see that you are located in the Ukraine. I have seen that large quantities of ex-Estonian, Latvian and Lithuanian .303 rifles from 1919-1939 have ended up in former Soviet Army depots in the Ukraine aftyer WW I.
and obviously a lot of Ammunition as well.
Inj 1919, the british Government supplied Estonia ( and the other Baltic states to a lesser degree) with surplus Long lee-Enfiled rifles and tons of .303 ammo, loaded in chargewrs marks I, II and some mark III style. Mostly mark II type ( with the straight long slots in the back). The ammunition is also mixed Headstamps ( WW I British and US Contract, some Kybnock 1920s contract, and also later S&B Riga “marka 7” .303 ammo.
In 1939-40,. when the Soviets occupied the three Baltic states, their rifles were taken into Red Army inventory, and saw some use in 1941-45 ( Irregular forces, Lake lLadoga Road and Railway during the seige of Leningrad (Propaganda Films, newsreels and still photographs show various usages).
Just recently, another Poster from Kiev (Kiyiv) showed phots of “Russified” P14 Rifles (with Mosin style stocks) from a storage depot in Ukraine. These were the US made British rifle on a Mauser Action design, in .303). They were also supplied to the Baltic States in the 1920s.
Have you collected your charger clips locally, or from all over the world?
As to the List of makers, some have already been identified, and there are lists of such stamps in Web boards dealing with the .303 cartridge itself.
G,GB Greenwood and Batley, Leeds, Britain:- Ammunition, and Arsenal Machinery & equipment suppliers
TF&S british maker…right up to 7,62Nato clips today
MB and MBO Australian (MB Bendigo Ordnance Factory, MBO Marybyrnong Ordnance Factory)
K Kynock Birmingham KN Kings Norton (Britain)
I am unsure of some of the others, but relating them to the type of Charger (if on Mark II, then British wartime producers during WW I) will give you a better idea where to look for answers.