There aren't very many catastrophic failures on the aluminum reciever HK .308 clones. It was originally a sheet metal reciever design, so there is not alot of stress put on it. The catastrophic failure was more speculation & rumor rather than documented fact, although I don't doubt it happened rarely. It happens with all guns time to tim. It isn't the danger that is the problem with these guns, it is the reliability issues.
The guns that run right out of the box seem to be okay and stay that way. But enough of them never run right from the begining or develope problems, that they have gained a bad reputation. There is nothing wrong with the design, it is just poorly put together by a mass production company. I suspect a big part of the problem is that these are built using surplus parts kits and cheap recievers. So the parts have varying grades of wear and are made by different manufacturers. While HK originally designed and marketed the HK-91/G3, the licensed it to several different manufactures such as FMP & POF. These than saw military use before being chopped up for surplus. If these were assembled one at a time by a gun smith who paid attention to detail, I suspect it would be okay. But these were done in batches where speed of assembly is what made it profitable. These guns cost new what a good gun smith charges for labor alone.
Springfield charged a premium for these guns at the time. They were 30-50% more if I remember correctly. Part of that premium is that they were backed by a lifetime warranty. So if you have a problem gun, it was worth the extra money to get it from Springfield.