In article , "AlexW"
says...
snip
Yeah, IIRC these are about £20 from wickes, my concern here is that
these are quite light approx 5 kilos I think ... will this give me
enough compaction?

I am also a bit worried that I might struggle with this type as the head
is about 10cm square and it might push the chippings around the sides
rather than down to a degree, where as with a wider plug this effect
will be lessened?

Only because you're spreading the force over a greater area, and the
proper tool will be easier to keep straight.

I know there will be a trade off between the weight and velocity of the
pound due to my physical ability lift and pound the heavier device.

Remember kinetic energy is proportional to the square of velocity, so
if you accelerate this downwards with a force of 1g in addition to
the acceleration due to its weight, it will be the equivalent of
dropping 20kg the same distance - and you'll be able to lift it
higher and use it longer than your 30kg lump of concrete.