The other caliber purposed by Frankfort Arsenal for the AR-15

During the development of the 7,62 NATO cartridge the US Project Salvo also continued with the idea of having a cartridge that fired more than one bullet.

By 1959 another cartridge was designed with the assistance of Frankfort Arsenal to replace the 222 Remington (5,56mm) for the AR-15 rifle,

The new cartridge used the 25 Remington cartridge modified and called the 6,35x48mm (also a 6,35x52 too). Winchester manufactured some of the cartridges WCC 59 and Frankfort FA 58.

The single bullet 6.35x48 fired a 70gr bullet at 3,345 fps while the duplex (FA-T127) fired a 54 gr bullet & 55 gr bullet at 2600 fps and 2460 fps.

This cartridge was tested in bolt action rifles and designed to be used in the AR-15 rifle but the 222 Remington Special became the 223 and 5,56mm cartridge used in the AR-15. My photos show the 25 Rem and 6,35 cartridges - green tip is duplex loading

I've always wondered about the duplex loading with ammunition as the second round will I think effectively push the first one when the 2nd enters the bore and obturates into the rifling therefore stopping any of the gasses from pushing on the first round.
One wonders as to a pressure spike once the 2nd projie starts pushing against the first as I cannot see any other way a duplex round would work is this a correct summation.

Nice rare rounds RCS very much enjoying the cartridges that are being displayed between us, I have a fair few wildcats in my collection as well.

I also enjoy talking about the different cartridges and sharing the photos on this website, which is the best website
for serious discussion of small arms and ammunition. I hope the membership also enjoys our cartridge postings too.

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Originally Posted by RCS

I hope the membership also enjoys our cartridge postings too.

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We do, I'm just reticent to go down and take pics of mine to post. I do have a couple but most are displayed here by you two already.

My Grandparents had popular science and Popular Mechanics from the 30s thru the early 70s.
The duplex 7.62 resulted in several articles in the early 60s (along with some really cool submarine propulsion systems that don't seem to have taken off).

Be interesting to hear what they said about them, I could troll through some of my books on ballistics not sure Mann covered those types his was more along the line of trajectory and the oscillations of the round in flight from memory.