I have a 30 with 32" barrel, im not sure if 24" is the same but mine likes zan 303 slugs, with the 24" barrel I'd maybe try 50 grain.
If you have the aea regulator, take it off and junk it or do like i did, gut it then bore it and use it for extra air, you can also just gut it to use for air but boring it takes a little weight out. The regulators are junk, you will eventually have issues, I have 3.
My number one hack I've done to all 3 guns is making .100 inch thick washers at work and putting in the valve spring retaining cap, this puts more pressure on the valve and keeps shots much more consistent and more per fill in unregulated guns, I have went through lots of ammo to find what works on max power and leave it there but if you want to shoot a variety you might need to play with the power wheel and possibly fill pressure if your unregulated. I noticed certain pressure ranges in two of mine that worked better before putting the thick washer in valve cap now I fill to 3600 max power the whole way, my 30 with 32 is a different beast, heavy hammer spring with valve cap washer, 4500 ,max power ,60 grain 303 slugs. Aea has been a bit of a pain to find what works the best and if you break anything you might as well buy another and have a parts gun or have access to a machine shop.