The SALVO II trials in 1957 included the standard length Cal 30 M1906 case in both duplex and triplex loadings. It’s been said that the only sure way to tell the two loadings apart, once they’re removed from the original box, is by X-Ray (or pulling the bullets). That is mostly true but unfortunately not many of us have access to the equipment to do this. Being a stubborn sort, I was determined to find another way. I was partially successful so, for what it’s worth, here’s what I found.
The external characteristics of the two cartridges include tip color, headstamp, and cartridge weight. It’s remains to be determined exactly what the tip colors mean and headstamps seem not to be unique which leaves us with the total weight.
The Duplex is loaded with two 96 grain bullets and the Triplex with three 60 grain bullets. So there is a nominal total bullet weight difference of a little more than 10 grains. Considering the normal variation in weight between powder charges, bullets, and empty cases, that’s not much to hang your hat on. But, I took the 10 cartridges that I had and weighed them. They definitely seemed to fall into two groups, the light ones weighing approximately 421 to 429 grains while the heavier weighed 432 to 438 grains. So, I took the lightest two and the heaviest two and pulled the bullets. Voila! The light ones were both Triplex and the heavy ones were both Duplex.
Coincidence or pure luck? That’s not a very scientific test and a very small sample - and I don’t know if the middle 6 cartridges would follow the same pattern but it’s better than what I had before. Use this information at your own peril. They are not cheap cartridges to be playing around with.