Kip, I subscribe the the UK newspaper database which is sometimes quirky to use:
https://www.britishnewspaperarchive.co.uk/

It looks like the trial you are referring to took place 28 April and was published in the 3 May 1879 edition. It appears the trial was to measure the velocity with which shot of various sizes powered by various charges of power in various gauges arrived at a target. I cannot find the test itself but there are numerous letters leading up to it and commenting on it. For instance, this is one letter from May 10, 1879 in the Field:

[Linked Image from i.imgur.com]

There is a reference to a Jan 25 1879 editorial which discussed a new "force meter" which was going to be used.

I'll continue to play around with the database using various search words. Maybe something will turn up.

Baluch are not Brahui, Brahui are Baluch