That is from working with SR 4759 myself..quite a bit..
I do a lot of experimenting with loads for training kids..
Sr 4759 is used a lot by cast bullet shooters..
it is bulky, and not position sensitive.. it ignites easily and is also very accurate..
you can run it lower than the 20 grains recommended as a start load.. and the 30 grains is a max charge for a 270 Win with a 150 grain bullet...listed on IMRs old Brown Data Sheet.
the large spread shows how flexible the powder is for the type of service in reduced load potential for training your 9 year old.
with a 110 grain bullet, the recoil at 20 grains for starters should recoil less than a factory 30/30 load, yet be flatter shooting and just as accurate at 100 yds as any deer load you'd ever need...
from the 20 grains, you can work up from there to the 30 as your son can tolerate the recoil... after that, for more velocity you can move up to IMR 4198 and/or RL 7.
believe me, you will find these loads, more accurate, with less recoil than many of the loads listed in Hodgdon's "youth loads" using H 4895, their favorite powder..
Hodgdon uses that data, as they got it for free from ADI which makes the powder.. Hodgdon has never done a ton of testing on it..they are a distributor... not a manufacturer..
Hodgdon also distributes SR 4759 and IMR 4198.. if they truly tested this stuff they would recommend these powders as they produce much better accuracy with substantially less recoil..
I get much of my starting data and parameters from Cast Load Manuals and IMRs old Brown Sheet that listed all of their powders for use in each cartridge from the fastest to the slowest...