Cal 30 Duplex and Triplex


#1

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.

Ray


#2

Great info Ray - thanks!

If we could get enough weights for known specimens, it might be possible to calculate a confidence interval for identifying the rounds by weight - i.e. there’s a 95% chance that if it weighs between x and y, it is a triplex. I’ll have to crack open my old statistics book to see how many samples would be needed though (probably more than people would be willing to sacrifice to the puller!).

Another thought - are the projectiles GMCS by any chance? If they are, I wonder if you could detect the indentation between the projectiles using a weak magnet?


#3

Chip

I think it would take a significant sample to arrive at any dividing line. And, even then, that line may be so narrow that there could be some overlap.

I am fairly confidant of the two extreme weights. It’s all those in between that will still need an X-ray.

The bullets are GMCS. I could not tell any magnetic difference. I even went so far as to photograph the bullets, enlarge the photo, and try to determine the ogive dimensions. But the ogives were so close that it proved a waste of time. Maybe if I had a $5000 Optical Scanner . . .

No one commented on the black bullet tips. It was purely coincidental that I had two light cartridges with a black tip. I think.

By the time we find some method that is more certain, all personal computers will be equipped with an x-ray built into the printer/scanner/fax/copy machine.

Ray


#4

If you ever x-ray your other cartridges I would be interested in the list of weights for each type. I agree that it would probably not be possible to come up with a meaningful dividing line given the small spread in weights. And even if we could come up with a 95% confidence interval, there’s still that 5% chance that you’re wrong. I personally prefer the 100% route.

One of my first thoughts was that my dentist has an x-ray unit that is hooked into a normal desktop computer - from what I can tell the whole thing is run by the computer. I wonder how much one of those costs and what kind of paperwork you have to do to get one :).


#5

Another great thread, Ray.

I found Chris Punnett’s .30-06 book (pp. 353-355) to have a lot of information and served as the primary reference to identify the rounds I have in my collection.

Details (left to right):

  1. Duplex, commercial case/headstamp with dark violet patch on base and remnants of red wax on projectile (total weight 28.80 g)
  2. Triplex + sectioned round. WCC 57 (total weight 27.63 g)
  3. Duplex? WCC 57 (total weight 27.65 g) might be a triplex based on weight
  4. Duplex WCC 57 (28.05 g)
  5. Duplex? WCC 58 (28.22 g)
  6. Duplex? WCC 57 (28.08 g)
    The difference between the last 3 rounds include very slight differences in the projectile ogive/meplat and the style of neck crimp (not visible in this picture).

Here are the long neck rounds I have. Position of the shoulder crimps are the key to identifying these rounds (high = duplex; low = triplex).


Details (left to right):

  1. Triplex WRA 56 (28.25 g)
  2. Duplex WRA 56 (28.62 g)
  3. Triplex WRA 56, black tip (28.33 g)
  4. Duplex, red tip (not wax) WRA 55 (28.91 g)
  5. Duplex, red wax coating, WRA 54 (28.55 g)
  6. Duplex, WRA 55 (28.93 g)
  7. Triplex, WRA 56, shorter projs, (27.99 g)
  8. Earlier type with longer case (76.7 mm vs 74.6 mm), Triplex, WRA 54 (28.88 g)

Do you have a trader on the short cased black tipped triplex round?


#6

Excellent information guys!!!
Might have to try and weigh my ones today.
I havent seen the black tipped one either, very nice


#7

I weighed my 2 examples today.
My one with no tip colour weighed 436.7 grains which would make it a duplex.
My red tipped one weighed 425.6 grains which would make it a triplex.

Unfortunately I dont have spares to dismantle and confirm but based on the superb information supplied by Ray I will be changing my decriptions listed in my files :)


#8

The only SALVO item I have is the projo from one of the squeezebore 9mmP.

I’ve always been curious about the projectiles used in the centerfire rifle versions. In the sections pictured, it looks like the triplex version has cannelured bullets, while the duplex bullets don’t appear to have the groove.

I know they used many different types, but I’m curious as to whether they ever employed standard commercial component bullets (.30-06, .32acp, etc.) or if all the SALVO pills were made with the project in mind.