If I combine a Pneumatic-pump Airgun and a Spring-Piston Airgun together will it be more powerfull?

I'm going to make a Pneumatic-pump Airgun which is combined with a Spring Piston Airgun. Now most of you guys will think it is more powerfull but when I thought about it I realised that the compressed air pressure of a Pneumatic-pump gun might push the bullet out before the spring piston reaches the end to create high air pressure or the pressure from the pneumatic will combine with the piston and shoot the bullet before the piston reaches the end (since pneumatic has given more compressed air, the piston doesn't have to reach the end) making it powerfull as normal. If I adjust the piston to almost reach end (creating high compression) and at the point, the pneumatic transfers it's pressure. Or the pneumatic pressure will be too late but still can generate slightly more power.
IS A PNEUMATIC-PUMP AIRGUN OR A SPRING PISTON AIRGUN STRONGER?-WHAT'S THE AVERAGE SPEED FOR A SPRING PISTON TO MOVE FORWARD AND 80PSI PRESSURE TO MOVE FORWARD IN A BARREL (IS IT THE SPEED OF SOUND OR SLOWER)?

Doh

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