Just picked up an 1899K Saddle Ring in 25-35.

I was thinking about trying some 100 grainers in it, but before ordering some was wondering how they fit in magazine. The 117 roundnose Hornady is fairly short, was wondering if say 100 Hornady or Speer will fit ok.

Yes the will fit if you seat them to fit..The rotary magazine is for factory length rounds...Nice gun and a real nice caliber...I shot many deer and a few elk with one in my cowboy youth...Found it capable if I got within a 150 yards and put the bullet behind the shoulder...I used the 117 factory ammo..I still hunt deer with that gun every year just for the heck of it, but I can't use the 100 grainers or the 87s as my gun is a Win. The twist may be your biggest problem in that Savage 99 as it may not shoot well with lighter bullets, guess you will find that out however....