I have almost the same configuration as you for my L3 project so I have done the math.

For a 4ft rocketman I get a decent rate of 21m/s (69 feet/s) for a 22kg (48lbs) rocket, that correlates very well with the rocketman drouge decent chart.

For the decent velocity you get (following Knacke)

With

**c_w** the drag coefﬁcient,

**A** the parachute surface,

**ρ** the air density at deployment altitude,

**M** the rocket mass and

**g **the acceleration of gravity g= 9.81m/s^2.

You should also calculate the opening shock both for your drouge chute and the main chute.

In the infinte mass model this gives:

**c_x** is the opening shock coefficent, its about 1.1 for the rocketman chute.

For the main the infinite mass model highly overestimates the force.

For deployment speeds of 200km/h (180 feet/s) you get something like 1600 N and for 300 km/h (270 feet/s) 3700N for a 4ft rocketman and a 48 lbs rocket.

The shock of the main under drouge is around 6000 N but this is in a region where the infinite mass model is wrong, so in reality it will be much lower up to a factor of 10. That is all for controlled deployment.

You can find almost anything on this in the Parachute Recovery Design Manual by Knacke:

http://oai.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA247666
With the freebag method and serial deployment you will highly reduce the change of entanglement.

The drouge should reduce the speed enough to restrict the main shock to a value your recovery gear can handle.

There is also a nice article by Jürg Thüring but it is in German:

http://www.argoshpr.ch/j3/index.php/knowhow/recovery/123-richtiges-design-von-bergungssystemen