Question about missing DV on Vanguard replica
I've created a near 1:1 replica of the vanguard rocket (it's TV-3 paint scheme on purpose) which put the vanguard 1 in orbit. The engines are all the exact ones used IRL, the dimensions as well as mass of each stage are near identical, and the burn time for the engines are correct too.
Despite this I technically have a little bit extra DV than enough for a 250km orbit (9677 m/s) which is nowhere near close enough for the 650km x 3966km orbit it has IRL.
The only thing I can see that's wrong is the 33KS-2800 third stage engine which in the test flight tab shows a 33 second burn time but the burn time from mechjeb shows 22 seconds. However, as far as I'm aware the propellant for that engine cannot be set larger than the 97.7L that provides it 22 seconds.
Does anyone know where this went wrong?
Update: After upgrading avionics and changing delta stage HP AL stringer tanks to HP iso I pulled 263kg of dry mass off which is the most I can do with 1957 tech. This gave enough dV for me to achieve a 204km x 2,787km on my best attempted ascent, still heavily short of the 650km x 4000km orbit irl.