Hi Marrakai and thanks for clearing my doubts about what a true Brenneke slug is supposed to be like.

Your reply would have been very encouraging had I recently not shot one slug into a cardboard box packed with glossy magazines. Penetration was approximately 4 1/2" and the retrived slug wasn't too different from the RC4s.

I will take a pic or two tomorrow morning and put it up here.

For the time being here's another view of the two slugs recovered from the earth bank.