I’ve seen more than one explanation for the tip colors. One is as good as the other I suppose. Some are also blue or black. A color tip often was used to identify the hole made by the top bullet, but not always red. I think there was a discussion about this in one of the issues of the JOURNAL. By Bill Woodin, as I remember. Or maybe Chris Punnett? I’ll see if I can find it.
Update - Found it quicker than I expected to. Here’s what Bill said:
[color=#BF0000]The 30-06 (normal case length) with the short pointed bullet, red tip, . . . is most certainly a triplex. These rounds have a dark red tip for identification . . . Duplex rounds . . . normally have plain tips, but colors noted have been light red . . . and dark blue. . . Target marking rounds have paint - generally a flat red - covering most of the exposed bullet. . .The only positive identification is by X-ray.[/color]
The long neck cartridges can be identified by the crimp in the neck so they are easy to ID.
Following a suggestion by Bill I weighed as many of the duplex and triplex cartridges that I could get my hands on and found that it is possible to make a good guess based on the total weight alone. Duplex rounds tend to weigh about 432 grains average whereas Triplex cartridges weigh a little less at 424 grains average.