Fine tune your thrust with 18mm motors!
4 x D9 will get you 78Ns total impulse... just block off the central tube.
You can mix D9-5 or 7 with D9-P to decrease the ferocity of the ejection pulse
You can mix D9-5 or 7 with D3-P for slightly less power
Explore the thrust combinations with Klima D9, D3, C6 and Estes C motors to suit your particular build!
Positive motor retention provided by two stainless steel washers and bolts. Hint: shorter bolts will give you a few grams less mass