IIRC, the rule of thumb is about 30G. So if your forward section in front of the shear pins weighs 5 pounds, then you want it to shear out at not less than 150 pounds force.
In a high speed horizontal deployment, you'll still deploy the main in all likelyhood. But for most other scenarios, the front will stay attached upon drogue deployment.
Gerald
Well the forward part probably doesn't weigh more than a pound so that means the 4x35lbf total of roughly 140lbf is more than enough in that department. But then that doesn't really count the drogue pull itself. I guess in a perfect world that should be about zero unless something screwed up so I shouldn't worry too much. Also, if the main goes at apogee I just have to walk farther so it isn't the end of the world. Does the charge sizing sound about right to you? I used the NASSA ejection charge calculator and that is what it gave me for the volume and pin number.