I've heard the lighter weighing 20 Ga.
shotguns can kick more with slugs
than the heavier 12 Ga guns.
Looking at something the G-daughters can shoot.
What experience has anybody had with these, and with the younger shooters?
Greetings to you in Uwharrieman in the Tarheel State. I wish I was living there again!
It is definitely not true that a 20 gauge slug will have more felt recoil than a 12 gauge slug, although it can
be true in some circumstances.
Basic physics applies here. Felt recoil will be a factor of gun weight and fit, besides the mass and energy of the slug.
Looking at two comparible Hornady slugs, we see the following:
20 gauge - 250 grains; 1800 feet/sec & 1798 foot-pounds of energy at the muzzle
12 gauge - 300 grains; 2000 feet/sec & 2664 foot-pounds of energy at the muzzle
Looking at semi-autos, let's say a Browning Silver, we find:
12 gauge Rifled Deer Stalker - 7 pounds, 12 oz
20 gauge Rifled Deer Satin - 6 pounds, 12 oz
and similar differences are found with the Remington semi-auto rifled deer guns. About a pound of difference between the 12 ga and the 20 gauge.
My experience has been that the biggest difference in recoil is that between a gas operated semi-auto and a pump or other fixed breech type gun, and that 20 gauge gas operated semi's are pretty reasonable guns to shoot 20 gauge slugs in.
I'd go with a 20 gauge gas operated semi-auto, and use the "managed-recoil" type slugs for practice/sighting in purposes (although shoot a few rounds of the actual slug you will have them hunting with as a final check on POI).
Benchrest shooting any type of slug gun, especially in warmer weather with light shirts on is not always comfortable. Make sure you take this into account before having your grand-daughters shoot practice rounds. The gun should have a good, modern recoil pad and you can also use shooting vests with Reactor pads or similar inserts.