Little history lesson !
The Marlin 336-44 was made from 1963 to 1967 . In the years of 63 and 64 the rifle had no saddle ring the years of 65 , 66 and 67 however did have the saddle ring . Forgive me but I don't remmember the exact number that was supposedly made but the non saddle ring guns are a bit more "rare" if one is into collecting/accumulating .
I have one of these also . Well actually it's the second one I've owned . Both of the ones I own or have owned were made in 1967 and both shoot and or shot cast nicely .
I just recently did some testing of the new and not yet released Ranch Dog 432-240GC mold in this exact rifle . You might rethink the 265 grain RD bullet and lean more towards the 240 grainers since recoil with an 11 year old might be an issue .
FWIW here are the max loads I shoot in the 336-44, the velocities are vaerages of my own loads on a brand new Chrony taken this past wednesday around noon . Temp was approx 67-69 degree's .
Ranch Dog 432-240GC 25 grains H110 , 1863 FPS
Ranch Dog 432-265GC 23 grains H110 , 1732 FPS
Ranch Dog 432-300GC 21 grains H110 , 1578 FPS
Mountain Molds / Ranch Dog 432-325GC 20 grains H110 , 1559 FPS
All four of those are max loads and obviousely can be stepped down from a good bit .
The two pics above were taken the day I got the rifle right before Xmas 2011 and it has no good Bushnell 3-9 on top . I've since replaced that with a nice old Weaver K3 and added a couple coats of Tung Oil to the wood .
Here are a couple recent targets shot with the 336-44 and the Ranch Dog 432-240GC .
The Ranch Dog 432-240GC before lubesizing !
And ready to be loaded !
Oh one final thing the Mountain Molds Ranch Dog 432-325GC is not something thats available to the public in mold form or in ready cast bullets . Thats a mold I had made up last summer to fill the gap between the Ranch Dog 432-300 and 432-350 . But if truth be told there wasn't really a gap there that needed filling , but I like the bullet nontheless !