I just took a case and loaded some 180gr Swifts and looks like the longest that will feed is 3.139". My magazine is still the original slantbox and feeds excellantly. Does not appear to have been modified at all. You could easily take 1/16",3/32" off the ramp and extend the box with little trouble if that would help. My COTW shows the 333 Jeffery Flanged at 3.49". Looks like it would be a stretch even with opening the box and taking some off the ramp. If you opened the back also would be no problem. Don't see it would be much trouble to do. Otherwise you would have to seat a little deep to achieve the length and don't see that as much trouble either. With the Swift I was a good 1/8" in front of the crimp groove. With judicious bullet and powder selection I think you could make it work easily. The barrel on mine is a premium M14 barrel that was incorrectly threaded I understand and salvaged on this rifle and a 30/40 worked easily. A 333 would be a nice application.