Good job. You turned some pretty rough looking shellcases into interesting pens. I like how you matched the "worthless wood" to the beaten up case.
Anybody who actually shoots 243 Win or 30-30 Win caliber should be able to distinguish between the two readily. I shoot and handload both calibers, and I also make pen kits out of 243 Win (why I don't make kits from 30-30 is a different topic).
Here is another photo which I hope proves illuminating. A fired 243 Win shellcase is on top; a fired 30-30 case is on the bottom.
As Jacob mentioned, 30-30 has a rim whereas 243 does not (it has an extractor groove instead). Note that the case head on the 243 is the same diameter as the case body. On the 30-30, the case head is larger in diameter than the case body.
Also, the case mouth inside diameter of the 243 Win shellcase is smaller (0.243" or about 6.1mm) than the 30-30 (0.308" or about 7.6mm). A 7mm slimline tube will fit inside the mouth of the 30-30 case with some slop, but will not slip into a 243 case mouth. A slimline nib matches the outside diameter of a 30-30 case reasonably well, but is much too big for a 243 case. In fact, you'd have to open up a 243 case mouth just to press the nib in.
The shoulder and neck lengths are also different. Note that the 30-30 case has a shorter shoulder and longer neck than the 243 case.
The shellcases you used have rims, no extractor grooves, a case mouth diameter matching a slimline nib and a long neck. They aren't 243 Winchester caliber - but again, they are nice pens.
I hope that helps,
Eric