1 gram in a 4" diameter rocket sounds a bit low even without shear pins. I use 1.2 gram on my 4" goblin (determined from ground testing) without shear pins.
Are the 20# screws 2-56? This is what I use on a LOC 54mm (2.6") rocket to hold the nose, but only one screw.
This then needs 1.2gram BP to reliably blow the nose off.
I have found it takes more BP than the calculators indicate.
Others should pipe in but I don't think to open end of the nose cone makes a difference.
My guess is at least 2grams of BP is needed. I would start there and ground test. Do a video of the test, preferably at high speed so you can watch in slow motion or step frame by frame to see the event in detail.
yes 2-56 is what it says on their website. I was also thinking that 2 would probably be enough screws, not sure why the default is automatically 3. Payload bay will contain a 36" nylon parachute (most likely) and a lightweight nylon cord. Nose cone is a plastic deal that came with the kit. Not super heavy,,, nothing up front on it is super heavy, though I may need to add some nose weight by the time I finish as my simulations are coming out less than 1 caliber of stability.
Noted on the charge maybe being a bit small. The plastic is a little bit unreliable as it seems to expand and contract a lot from 70degF to 90degF (at 90 it fills the tube nicely, 70 is super sloppy fit).
My first dual deployment testing will likely be my little yellow monster which is a 38mm tube and I'm confident in the friction fit on the nose cone with that guy. 0.5-0.6 grams of powder seems to pack plenty of punch and might tune it down a lil before doing my first in the rocket test on that one.
2 grams just seems like a lot to me, that's 30gn which is about how much smokeless powder I would put behind a rifle cartridge. I realize this is very apples to oranges but hey, that's what testing is for right? I also plan on putting some aluminum inserts inside the tube where the shear pins will go, just to make sure they have a solid place to shear. I'd imaging distortion of phenolic would probably make a difference in their ability to snap off.
TY for the comments on the nose cone, good to get that opinion. Basically a couple schools of thought on that and I think a lot probably has to do with how quickly the gas is filling everything up and where it's coming from. Or perhaps expanding actually helps a bit like how the skirt on a pellet works.
The number of pins you need for the nose cone has a lot to do with the weight of the nose cone and your recovery gear and how strong your apogee charge is. If you use a large charge that causes the upper section to slam to the end of the apogee shock cord, the pin(s) have to hold against the inertia of the nose cone and recovery gear hitting the nose cone. You'll probably need an extra pin or two. That will then require a larger main charge to shear them. The whole rocket is a system and you have to test your rocket. What works for one may not work for others. A recommendation for a number of shear pins makes a lot of assumptions about the rocket and some of those assumptions may not be correct for your rocket.
Test, test, and test. The cost of a dozen or so ematches shouldn't stop you from making sure the whole rocket is working correctly and that you get the whole rocket back in one piece.
Is there a way to test for this on the ground? Should I drop the loaded ebay/payload/nosecone from my roof on a tether to see if the nose pops off when the shock of the cord tensioning stops it moments before hitting the dirt? Or perhaps test a charge for the apogee simulation with a short shock cord? Hmm, got me wondering now how to really know how big a difference this would make.
Ematch kit is ordered along with some motors for my smaller rocket, so hoping if everything gets here and tested on the lil one I can do a low altitude flight on an MPR at NARAM without worry of losing it and have the drogue backup good enough to ensure she'll survive a hit on grass. That will be my first dual deployment flight, but I'm not sure it'll be ready, so I may have to test it in one of my neighbor's fields,,, but I don't think they'll be too keen to be launching out here rn, we've gotten very little rain the last month and everything is prolly too dry to be launching rockets. Plus I don't have any of that aluminum bar stuff.. So will prolly delay a month at that point.
