I've used 3 grams for my BDCR rocket for years and it was plenty. It was 6" and at least 24" long and it tested OK with 2 gms. I went to 3 for safety. The calcualtor said 6 grams as I recall and it was too much in my opinion. It got it out sufficiently violent but as I mentioned half did the trick. Of course I use pistons.

Doug

Too many variables out there to determine the right sized charge without adequate testing and checking for pressure leaks and conditions. Still better to incrementally experiment than to double the charge. Too many powder calculators to chose from. I've had great success with the calculator found on Rocketry Online Info Central Recovery Black Powder Use.

Ok
I doubled the charge. And put a foam seal on the ebay.
I was looking at Mike Konshacks load on his web sight.
7 grams. Blew the nose cone through my canvass tarp 😯
It worked.
hmmmmm.......

Just a note. As You know 'fit' has a lot to do with charge size also.

What fits at 50 degrees. Does not fit the same at 80 degrees.

My last core sample was using the same charge as previous four
or five flights.

My nose cone fit much tighter in hot weather.

I always seem to overdo it a little.....A couple times I had three
or four people look at Me at the same time, 😳 after my air cannon
has gone off. 😯 ... Thats one reason I like extra-extra long shock
cords.

I never could find ffffg when looking for powder. I got fffg.
There is a big difference when I use My fffg or use the ffffg
from a reload kit. I try not to use My fffg.

I have found that containing the powder in latex rubber tubing reduces the amount of BP used dramatically and is more efficient.

http://hometown.aol.com/tfish38/page16.html

Here is where I learned it from. It is all I use now - everything is nice and contained - no powder to spill or worry about spilling.

Edward