Well one idea is to increase the health of Smoke actor. Download Sanny Builder and open main scm file:
"C:\Program Files\Rockstar Games\Grand Theft Auto San Andreas\Data\Scrypt\main". The text will show up. Find this line:
|// Originally: Just Business|
Then type this into text search:
|Actor.Health($ACTOR_SMOKE) = 500|
Number 500 is a health of Smoke actor. Increase that number and click run - compile. Smoke now has a biger health.
The other idea is to decrease the value of damage made by Mp5 gun in weapon.dat (I think it's 25 but I'm not sure because I don't have SA installed at the moment).