Hi Ghostrider

If you go to Nitro Express forum, in the section on Classic Single Shot rifles you will find a thread on “Interesting Rook Rifle, Mini Snider in .360 No.5”

There is some useful loading info there. I know that your rifle is marked as a .380, but the outside lubricated .380 Long with heeled bullet and the slightly later inside lubricated .360 No. 5 seem to have been regarded as interchangeable.

Hope this helps!

Parabola