The action is plenty strong, so that isn't the reason, and I'm sure Ruger would tell you the same.
I had one in 378 Weatherby at one time, 1/2 MOA rifle too, believe it or not.
My brother is building a 500 Jeffery on one to shoot 750gr A-Max bullets right now, just finishing up the stock on it and it's done. It's got a 36" barrel too, mine had a 28".
Call Dave Caboth at Nitro Gun Works 907-376-5261 to get the scoop on these actions, he uses them for big bores like this all the time. He's the one that bought mine off me, and to build a bigger one than the 378 on it too.
Problem:
The forend's on a hanger, not condusive to freefloating the barrel. My bother is bedding his 500 full length I think.
Accuracy is probably slightly better with a bolt action, thus it's the most desirable for LR work.
I'd buy one again, it definitely makes a short package using a long tube. Accuracy was never an issue on mine.
Dave tells me the early model ations up through the 80's are the better ones, I forget why exactly.
Like Phil said, a lever action at the bench isn't the best, but it does work.
Mine had a Timney set trigger, couple ounces to a couple pounds.
[ 12-13-2003: Message edited by: Brent ]