It WILL change the velocity, how much depends on what caliber, load ect...... As for accuracy, it can make the rifle harder to shoot accurately, but it won't make it inherently less accurate!

I have a light weight 7 express Rem. (280 Rem.), and the bbl. is less than 22"'s long, but i've shot a lot of 1/2" 5 shot groups with it at 100 yards useing my hunting loads!!

I've had several other short rifles that shot well too.

Drilling Man