I will take a wild stab at this...This is built by Century? Century employs monkeys to assemble rifles. Occasionally they get it right. CETME receivers should work with HK magazines, but sometimes they are not configured correctly. The mag well may need to be tweaked. The rifle is marked .308, but is actually intended for 7.62 X 51 NATO ammo (there is a difference). Many Century builds have what is called "ground bolts". The CETME/HK-91 do not headspace in the traditional sense. You measure "bolt gap". This is the area between the bolt head and bolt carrier. .020" is good. .005 is not good. Century would grind some material off the back of the bolt to get want is called "false gap". You can also get false gap from the charging handle bottoming out in the channel. Almost all of these rifles were assembled from imported/used parts with some US made parts thrown in to be in compliance with Federal section 922r. Because these are used parts, they might not be clean. A good thorough cleaning and inspection is the first step.
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