I agree with everything said by bobkrech. Especially, someone with multiple casings to choose from will choose a reload for the effect and desired altitude for the rocket rather than on cost per Ns. Someone buying their first casing of a given size, however, might consider cost per Ns as one factor in their purchase. They might wonder whether the product line from one manufacturer is generally more or less expensive than from another.
I have expanded my spreadsheet to include all reloads from 24mm to 54mm sold by Wildman and Performance Hobbies. This includes 8 product lines. For the most part, there is a great deal of overlap between product lines. The variation within product lines is at least as large as that between different product lines. I can see very little economic reason to prefer one manufacturer over another, with the following exceptions:
a) In MPR, Aerotech hobbyline has the edge. The closest competition is from Cesaroni, whose 24mm and 29mm motors are generally small HPR motors, not MPR motors.
b) At the low end of HPR, Kosdon TRM, Kosdon by Aerotech, and Ellis Mountain have the lowest cost reloads. These do not include ejection charges, however, and Ellis Mountain does not use motor ejection, so the comparison with other motors is not exactly apples-to-apples. Also, I'm not sure what the future holds for Kosdon TRM or Ellis Mountain, but Performance Hobbies currently does show these motors in stock.
In 38mm and 54mm motors, reloads from these manufacturers seem competitively priced.
(Spreadsheet exceeds TRF size limits. PM me for a copy)
Kevin
Thanks for adding the other reloadable motor manufacturers to the spreadsheet. The manufacturers you added, Kosdon, Ellis, Kosdon by AT, Loki, Gorilla, (and the old AMW motors) all use the Kosdon C-ring style cases that use an aluminum forward closure and a graphite nozzle, both of which are not consumed in a flight, so with these reload kits you are essentially paying for a liner tube and the propellant grains. You're not paying multiple consumable parts, nozzles, or preasssembly, so these reload kits should be, and your spreadsheet shows, that they are the least expensive, and the cost per Ns doesn't change much with casing size as it really is the propellant that determines the cost of the C-ring casing reload kits.
I think it's fair to say that the propellant prices for all manufactures is competitive, but the cost of a reload kit isn't just propellant. In mid-power and L1 motors, there are 3 distinct casing designs with widely differing internal configurations. AT clearly has the most selections in the mod roc reloadable market with two distinct casing lines, one for newbies entering the mid-power world and a second for high power folks who occasionally fly mid-power. They developed this market and clearly dominate it.
Kosdon style casings are a simple and relatively low cost high power motor casing that employs minimal consumables. While a few reloads are in the mid-power impulse range, many are classified as high power reloads by high average thrust (>80 N).
Similarly the CTI Pro24 through Pro54 casing design employ a preassembled reload cartridge that is threaded into a light weight casing which is the only reusable part. CTI initially produced mainly L1 and L2 high power reloads in the Pro38/54 style casing, with a couple G impulse model rocket motor reloads, but recently downsized the design into 29 mm and 24 mm casing but many of these reload are also classified as high power reloads by thrust.
You pay for the convenience of a preassembled reload in smaller motors compared with AT, so CTI motors below J cost a bit more than the equivalent AT motors. Likewise there is slight discount with Kosdon style reloads compared with AT below J-impulse because of fewer consumables, but the companies manufacturing these reloads are smaller and do not have the distribution or production capacity of AT or CTI so they are harder to find.
When you get to J-impulse and above, you are paying primarily for propellant so costs tend to be competitive, and this is what Kevin's master plot shows. Ultimately, what you fly may depend more on what is available locally so you don't have to pay a hazmat fee every time you buy a motor.
Bob
