A possible suggestion for a Friday video Andy, although you have just covered the FX slugs.
I did make some of Mrs ARR's ballistic gel. A friend of mine and I then had great fun shooting it with my new 0.177" TX200 (chronoed at over 11 ft/lbs) and his 20 year old 0.22" BSA Airsporter (chrono-ed at ~8.5 ft / lbs on the day). Using similar pellets in both calibres at at 0.5m and 20m, diablos, hades, H&N piledrivers, H&N hollowpoints etc, his lower powered 0.22" penetrated further consistently than my 0.177"! Yes I was surprised too.
I know 12" of ballistic gel isn't the same as a wood pigeon or rabbits head, but it makes you think about the old adage about 0.177" for feathers and 0.22" for rabbits, etc.
Has anyone else tried ballistic gel with different calibers at the same power? Is it worth a video in the future Andy?