Bigcountry, I didn't copy that from anywhere. Learned it in gunsmithing school. Since I have been there, more than one has come into the school from regular customers in the Denver area with this exact problem. The bolt rails have three perfect indentations from where the locking lugs would over rotate at the end of its rearward stroke and beat up the rails. The only thing that can be done to is is to file down the rails back to smooth but that is only temporary.
The newer 7400 have a little different bolt design but the problem still exists, it just takes a little longer for it to show up.
Most of the ones I have seen jam, have been cleaned poorly with way too much thick oil
Yeah, that's another problem people have with all autos. People seem to think that they need an entire bottle of oil inside the gun for it to function. Then they wonder why it won't work.
I just love it when I get a gun on my bench that has oil dripping out of the receiver and then I open it up only to get to clean off gobs of grease from all the parts.[:'(] I guess it's better than having to sand blast rust off the parts and receiver though.[:'(][:@]