Friday, March 21, 2014

Cubic Inches, Part III


193.7 fps

ERJ propellent 2.0 was tested.  I do not know if it was completely dry but I am an impatient kind of guy.

16 ounces of corn starch was charcoalized until no more gasses were being given off.  To my surprise, it was almost like a switch being flipped.  I measured 3.5 ounces of char (including the weight of the bag.)

I had 2.7 ounces of charcoal after two trips through the grain grinder.  A huge difference from the 11 ounces from ERJ-P 1.0.

I combined it with 11 ounces of commercially available potassium nitrate.  I dry stirred it.  Then wet with 6.0 ounces of 70% isopropyl alcohol.  Paste was passed through grinder one more time.

Paste was fluffed up with fork and dried under a heat lamp until isopropyl smell was gone.  Material was sifted to eliminate big chunks.  100 grains were measured out. and fired as before.

No hang fire was detected.

Audible "POP" at firing.

Chrony registered 193.7 fps.

I was pretty happy to see some progress. In terms of  "energy" the new batch generated about 9.5 times more kinetic energy in the projectile than ERJ-P 1.0

The Plan

Continue drying it out for two more days and replicate test.  I really do not know if this batch is completely dry or not.

Go to Yea-Old-Big-Box store and buy more corn starch.  My plan is to test multiple batches of propellant with varying amounts of charcoal.

Design of Experiment:  

KNO3 standardized at 10 ounces as that is an easy batch size to handle. 

Ounces charcoal           % Charcoal (of total)
       1.5                                 13%
       2.0                                 17%
       3.0                                 23%
       3.5                                 26%
       4.0                                 29%
       4.5                                 31% <====maximum listed in literature

Addendum added March 25:  

A small quantity of ERJ-P 2.0 was dried with a heat lamp overnight.  100 grains was loaded up and fired as before.  367 fps was measured.  That is about 3.5 times more energy than the 196 fps measured with the "green" powder:  Take home lesson,  Make sure your powder is dry.

To be continued


  1. Came over from the Woodpile Report - great set of posts on 'propellant'!!

  2. Thank-you for reading and commenting.

    I wish my progress was a little bit quicker. If nothing else, it shows that you cannot just pull something off the internet and have work without actually experimenting with it.

    Remus is an outstanding writer and quite the Renaissance Man. I am honored that he thinks my dinking around is worth mentioning.

    Again, thank-you for your kind words.

  3. To funny as I have been doing similar tests. 7 parts 3 parts 4 parts charcoal , as a propellant use powdered sugar.... Rockets only Never in guns. Some place I read that what type of charcoal has a lot to do with burn time, hardwood vs soft. I've been using oak, maybe thats the problem.