Batch 2018-batch-01

A slightly improved "repeat performance" M reload for my CTI Pro75 6xl case with Loki nozzle and forward closure.

Using Terry's #50 "short" Loki nozzle, we need a 38" liner and have just under 37" available for fuel. Using dash-143 buna-n o-rings as grain spacers, let's try 7 grains of 5.205" length, or 132mm, using Delrin coring rods of 0.75" diameter. This will be slightly more progressive than the 8-brain config last fall, but all parameters look good and it's a tad more propellant due to one less inter-grain gap.

The simulator says this could be a 34% M-2593.

Based on previous experience, there will be enough shrinkage to necessitate a "topping up" of each grain after the initial pour cools.

The simulator says we need 4919g of fuel for these grains, so let's melt a batch size of 5kg:

• 65% KNO3, 3250g
• 35% Sorbitol, 1750g
• 1% red iron oxide, 50g, added after melt
• 75 drops Polystep-B1, added before pour using eye dropper

This formula is completely fluid with 225F indicated on the Presto Multicooker, but viscosity is noticeabley lower making for easier pouring at 250-275F.

Grain fill lines 120.6mm from the bottom of the casting tube.

These grains were cast on 2018-07-05.

Results

Had to cut about 11mm length off one grain to make things fit, chose to do this to the grain with rough core.

• Grain 1, 670g gross, 17.63g casting tube, g net propellant
• Grain 2, 668g gross, 17.55g casting tube, g net propellant
• Grain 3, 674g gross, 17.72g casting tube, g net propellant
• Grain 4, 672g gross, 17.76g casting tube, g net propellant pre trim
• Grain 4, 610g gross, 17.76g casting tube, g net propellant
• Grain 5, 664g gross, 17.70g casting tube, g net propellant
• Grain 6, 666g gross, 17.61g casting tube, g net propellant
• Grain 7, 668g gross, 17.64g casting tube, g net propellant

Average casting tube weight g. Total propellant load g.

Revised simulation says this will be...