Then you should look at "Most AEGS" You'll find the most common are m4 and AK variants. Something with a barrel of a length equivalent to that would be average.
Or you could look into a bullpup rifle. You'll get a longer inner barrel length, but with a smaller overall rifle, which sounds like it would suit your needs.
Not for glory, nor riches, nor honours, but for freedom alone, which no good man gives up except with his life.