>>64229630
Old types of plastic we stopped using long ago do old outdated plastic things. Can't really explain it; I think sometimes it's a bad reaction with gun cleaner that got on it long ago, sometimes it's storage conditions (temperature), sometimes it's bad plastic batch. Kinda like how old zinc/ZAMAK parts can go crumbly if the mix was contaminated with the wrong metals. Or how tin, like on a tin roof, can develop tin pest. Hell, Stevens Tenite shotgun stocks are wood based polymer and can actually go moldy. Old plastics (~pre 1960s/1950s) are wild things and not the most predictable, even if they are very very durable (I've dug up some of it that was thrown away in the 50s/60s/70s, I'm sure).
I wouldn't worry about it if your gun has a good trigger guard and you know to keep cleaners off it (as you should any wood), but mine was bought already "shrunk". Maybe it's just the oils coming out of it causing it to shrink, I don't know. Like how silicone molds can lose their oils and deteriorate. Mine actually "shortened" and straightened out and pulled away from the grip and trigger. Around the screw it was its correct thickness because it couldn't compress the screw so it bulged back out to correct thickness at those spots. Never saw anything like it and I've never found out what kind of plastic they used.