[sc_rufctr]

A couple of suggestions....

Clean it... Not just clean but perfectly super clean. Stiff brush and lots of solvent.
(Check the chamber and internals for wear or fowling... Extraction claw?)...
Super clean the rails but don't use anything abrasive. Clean and check the magazine well and feeding neck. (were the bullet leaves the magazine)

Back in the day we used to use a coarse cleaning cloth with gun oil. It wasn't abrasive but very good for cleaning.
I can't think of its name but not abrasive. More like a thick woolen fabric but not woolen. Does that make sense?
We used pieces of the same cloth for pulling through with a string of a 7.62mm barrel.
It was marked with a red line every 40mm. About 3 inches wide.

If it still jams after cleaning with good factory ammo then maybe a trip to a good gun smith is on order.

Hope it works out. (excuse my terminology)