CONGRATS to your son for a fine shot which was well within the range of his Model 99 in .300 Savage caliber.
I use a 1953 Model 99 in .300 Savage as my "go-to" deer rifle, but limit my shots to 250 yards or less due to my 76 year old eyes... even with a 3-9x scope.
I also hand-load my ammo for my .300 Savage. I've been reloading for the past 50+ years and your business-owning, archer friend should stick to shooting arrows because he obviously doesn't know very much about the .300 Savage cartridge or the Model 99 Savage rifle which is "THE" most accurate lever action rifle ever made. It is NOT uncommon for a Model 99 to shoot 3-shot groups at 100 yards into LESS than one inch. My Model 99 routinely shoots my hand-loaded hunting loads into 3-shot groups that measure 3/4ths of an inch at 100 yards. This kind of fine accuracy is commonplace with Model 99 Savage rifles.
Depending on your son's rifle's "zero", it would and could take deer out to as much as 500-600 yards or more. However, at those extremely long ranges (for a sporting rifle), it takes a great deal of practice to be able to accurately put your rounds into a deer's kill zone. However, both the Model 99 and the .300 Savage cartridge are capable of killing deer at those extreme ranges.
My own handloads parallel the supposed factory loaded round's muzzle velocity which is 2630 fps using a 150 grain bullet. My handloads chronographed at 2635 fps with a standard deviation of only ± 3 fps (+1 fps/-2 fps). I use 40.8 grains of Hodgdon's H4895 rifle powder which is one of their "EXTREME" powders meaning the velocity it produces is NOT... repeat, "NOT" temperature sensitive.
Therefore, while I might "zero" my rifle on an 80º day at my club's rifle range, if I take a shot at a deer when the temperature is only 15º above zero, the point of bullet impact should be the same as it was on the 80º day... i.e., 2.75 inches high at 100 yards, dead "on" at 210 yards and about 3 inches low at 260 yards. As you can see, using Hodgdon's EXTREME powder giving the SAME point of impact is a decided advantage over cartridges loaded with other, temperature sensitive powders... and most rifle powders ARE "temperature sensitive"!!!!
Normally, I never recommend attempting to shoot live game animals at extreme ranges simply because most hunters are not capable of shooting accurately at such extreme ranges, but NOT because the rifle and caliber won't get the job done at longer ranges!
Jus' my 2¢ plus 50 some years of big game hunting experience...
Strength & Honor...
Ron T.