Eley .320 Short rounds

Today I got two .320 short rounds.

One is unheadstamped, folded head construction, with rounded copper Berdan primer cup. The bullet is solid RN lead. When pulled it contained black powder. Even though it is unheadstamped it resembles early Eley rounds.

The other is headstamped "- ELEY - .320, solid head construction, with flat copper Berdan primer cup and no headstamp. The bullet is solid RN lead . When pulled it contained fine revolver cordite.

What were the dates these loads were produced between?

In spite of some intensive research - I have never been able to accurately date the introduction of the .320 ctg. Some would have it as early as 1865 - but I am doubtful. If that were the case - why bring out the .450 with Boxer case construction in 1868?? I suspect the .320 & .380 were first made about 1869/70 - but only conjecture on my part.
The cordite loaded .320 would have first appeared around 1900.

Thanks John, I thought you would know the answer to this.