totally agreed. a stack size of 50 is fine for the rebar gun since it shoots slow and thus depletes the ammo slowly.
However, such a small stack size for rifle is not very useful a full-auto rifle that consumes 10 rounds in the same timespan a rebar gun consumes 1.
The damage of the rifle is also not much compared to the rebar.
So, in my opinion, the current rifle in the game is not well balanced at all.