From people, video's and shreds I have seen at the launches, when it is a fast rocket it seems it is either the fins or the coupler that fails. My fins are very sleek and bolted into the ring so no worries there. What worries me is the couplers. The rocket is 3" diameter, about 80"s long, K650 or K570 first flight. See my building thread. Should go 900MPH if the wind is nice. So I have on coupler that connects the lower fin section to a tube that holds the drogue bay, this will be connected with 6-8 small plastic rivets, I want it removable so if it were to zipper or dent it could be replaced, it is a 3" coupler, I also have 3"s of FWFG coupler that holds the drogue in, this parts worries me the most because it is an actual deployment section and cant be held down with 8 rivets, it will been stug fitted and have 3 2-56 nylon shear pins. Then the upper 3"s of the FWFG alt bay is attached to the main chutes body tube, with 6-8 small plastic rivets. The nose cone will have three 2-56 nylon shear pins but I am not as worried about it. So what do you think? Is 8 plastic rivets enough to hold it in? What about for the drogue deployment section, is 3 2-56 shear pins enough? BTW, the lower coupler and all body tubes are phenolic, the coupler is as I stated FWFG (filament wound fibergalss). I have never flown into this speed regien with larger rockets so please, any helpful hints would be great... from what it seems, you want all sliding parts to have a tight fit and some sort of other device, either a shear pin or rivet, to hold it in there. Will I have any problems shearing the 2-56 nylon screws with a tight coupler as well? Normally when I use shear pins I have a loose fit with the body tube... guess some ground testing will answer that question.