Every missing ST point reduces hit chance, hopefully you can compensate by having higher skill.
You can also raise your ST during a combat situation by using drugs. A 10 AG build works with both nuka and buffout, giving 2 ST point and puting you at 3. In the end you will most probably need 300 skill (max) to shoot properly.
Sniper and most crit builds in general have 1 ST because they have to spend special points everywhere, perception, endurance, luck.