hoot, I suspect you are aware that the hazards of too-long cases is much different from any effect of cartridge OAL. "Crimping" a bullet in a too- long case will surely play havoc with chamber pressures! Actually, you probably are okay now because MOST chambers are quite a bit longer than normal max case lengths, sometimes as much as .030" longer! But, the risk of of being wrong here is pretty scary.
I lathe turned some "Sinclair" type case plugs for each caliber I load. I just turned a half inch long section of brass rod to bullet diameter, then turned the last 50 thousants to a bit over the maximum case neck diameter so it won't pass the chamber mouth and cut it off square.
To use, I trim a case 60 thousants short, seat the plug long, and chamber the "cartridge" to seat the plug to the actual chamber neck length. Then remove and measure the chamber length with a dial caliper. I do this a few times to make sure I have an accurate reading but, so far, the lengths are pretty consistant each time I do it.
It's easy to make the little plugs but, unless you have access to a lathe, I'd suggest you get them from Sinclair. Individually, they don't cost much.
Failing that, you might make a chamber cast that will give you a mirror image of your whole chamber. I make chamber casts with melted drug-store "Flowers of Sulpher" (a "brimstone" flammable yellow powder!) but the best stuff is low temp "Cerrosafe" casting metal from Brownell's.
Either way, using a chamber cast or a case length plug will let you measure with some accuracy the neck length of your chamber so you will KNOW what your safe maximum case length is!
