Hmmm ... I may just have to order another .303 extractor myself! Actually, Dale ... if you are thinking of ordering from Brownell's as suggested above, how about ordering an extra one for me, and I can get it from you at Muster ...?
I just went in search of the one I already own ... to have it in hand while responding to the case-length issue raised by Pony Express ... but I can't locate it! (Probably tucked away in my kit somewhere, but ...
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As for the possibility of the .303 extractor not working on a .30-40 Krag case because the latter is .1" longer (actually, only 0.072" difference in the SAAMMI specs) I doubt that would be a problem. These extractors are designed to push the spreading "claws" well past the case mouth so they can open fully into the chamber ahead of the case mouth (either by "spring action" or by a plunger being forced back into the shaft) then, when the tool is extracted, they pull back until they engage the case mouth. Some designs are also length adjustable ... by screwing the shaft in or out of the base ... although I can't tell from the photos on the Brownell's site whether this .303 extractor is adjustable that way or not.
Anyway, while searching, I did find the broken case extractor I have for all of my Cowboy Action rifles chambered in .45 Colt. When I went in search of one, I could not locate one made for .45 Colt - perhaps because rifles and carbines were not chambered for that cartridge historically. Nowadays, there are lots made for cowboy action shooting (which is possible because of the 20th century re-design of the .45 Colt casing to give it a wider rim and an extractor claw groove ahead of the rim) so maybe somebody makes one now. Back then however, I tried out a buddy's extractor made for .44-40, and it worked like a charm on .45 Colt (despite slightly different case lengths and mouth diameters) so that is what I bought ... and why I figure that a .303 extractor will most likely work fine for .30-40 krag ...