Colt 30cal SSB rare experimental cartridge

Dan Dietz thought it was an SSB round used in a Colt gun. I agree that the projectile looks SSB. But the headstamp is commercial. C.Punnett covers RICA in his book but he says the headstamp is “Superspeed”. I could not locate anything about it in his book. So, what is it, a fake?

That’s the most common head stamp you’ll find on the 30 SSB cartridges. It also shows the dimple in the primer from having been chambered in the M1 Garand rifle. It was developed by Colt for a special M60 MG.

It looks very plain vanilla to me.


Ray, do you know where in Chris’ .30-06 bible it is? Which page?

No not a fake. These are not .30-06 length like Chris notes as being from RICA. This is a Colt Salvo Squeeze Bore Project triplex load. The headstamp and light ding on the primer are correct. Virtually all of these were chambered, as can be seen below, which left the primer ding.

Some dummies with empty primer pockets (in new cases) are known as is a (+) WCC 71 loading with the front bullet seated way out.

A box

Vlad, no, I don’t know. It 's a 7.62mm based cartridge so I’m not sure why CP would have had it in his 30-06 book.

Thanks to both of you. I went after the headstamp without any measurements. I found the whole story (and more) here Why were these tested in a Garand? Would not measurements be good enough? I measure this round as 8x57.6mm with my metric calipers. What was the official designation?

Vlad the box in the photo has the time of development and the official Colt name on it.

As for testing vs measuring, I have four with slightly different case lengths. the WCC variation mentioned above is 58.26mm, & the three live R-P examples are: 58.13mm, 57.56mm & 57.99mm. Shoulders seem to be in the same place on all.

PS Russ Robinson didn’t develop these in 1903, that’s a typo.


Why were they tested in a Garand rifle? I have not seen any documentation but the story on the street is that Colt wanted to be sure each cartridge would function in the modified MG before they were linked. A Garand with the correct chamber was an easily fabricated test vehicle. The Garand has a floating firing pin that leaves a small mark on a primer when a cartridge is chambered, therefore the dimple. Things were a lot simpler in those quaint days.

I’m not convinced that these cartridges are as super rare as some have suggested.

BTW, where does your “8 mm” measurement come from??


I measured the projectile base at the junction with cartridge’s mouth. Non digital calipers, so maybe it is my old eyes.