The mid 80s P226s w the "scalloped" frame rails do it more than the older or newer guns, but as Charlie said, they all seem to keep working for some time when they do it. Point of impact/reliability might change a bit, or not. Some never notice the cracks until they look real close.
SIG added some cut outs in the frame rails (and some other mods) in the mid 80s for the M9 trials thinking it would improve reliability. Guns were more reliable than P226s in earlier M9 trials, but not as durable (two test guns cracked frames around 6-7K rounds, earlier guns did not). Jim Pledger, retired FBI/FTU told me it wasn't unusual for FBI SIGs to crack frames during an agents first 5K rounds in training (he worked for Glock then, wonder if he still mentions that now that he works for SIG?). SIG dropped that rail modification and the rails hold up much better much longer, like they did before. Hasn't been a problem for some time, but there are a lot of the older guns out there getting older, so the issue keeps popping up.
If it ain't broke, don't fix it?
Another thing... SIG recommends replacing the slide roll pins in the older guns every 5K rounds, or w new pins if you take them out earlier for some reason (don't re-use them, replace them). If you don't, they can loosen and cause the breech block to stress the slide/frame in a way that may lead to cracks, according to Todd Green, SIG's Govt and Mil Project Mgr (formerly of Beretta USA). That and scalloped frames in older guns may have been what caused the cracks in 52 of Baltimore County's 1300 P226s a few yrs back... RTFM?
