Finding starting loads for wildcats

Equalizer

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How does one choose a start load on a wildcat cartridge? I’ve heard of the Powely computer but never seen one…

I have a 358 Hoosier (358 Winchester shortened to 1.8”) and I have a great accuracy load but when I ran it over the magnetospeed it only clocked in at 2330 fps…. I’m using 36.3 Gr of IMR 4198 over a 180 Gr Barnes TTSX, Hornady 358 Win brass trimmed to 1.8” F210. Shilen 22” barrel.

When I look at regular 358 Winchester load data I’m seeing IMR 4064, Varget, Tac and other powders that I have not seen data for in the Hoosier. Do I start 10% below the starting load for the 358 Winchester?

The guy who commercialized the Hoosier said it would almost duplicate the 358 Winchester (180 Gr @ 2600 fps)

After this deer season I’m going to work up to my rifles max with my recipe but wanted to have the option of different powders and projectiles and an idea of where I’m close to topping out with IMR 4198.
 

MagnumManiac

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Feb 25, 2008
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Powley, QL or Gordon’s Reloading Tool will help.
I have a formula for determining start loads, pretty sure it is derived from Powley’s work.
It is too complex to write here, but you can look it up on the interweb.
It helped me immensely with my 338-416 Rigby Improved, as even 338-378 Weatherby data was off.
Gordon’s Reloading Tool is free to download, I haven’t played with it yet. My computer is being used for other more important stuff.

Cheers.
 

Jud96

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I really like Gordon’s Reloading Tool (GRT). It’s free to download and has been very close when the data put in is accurate.
 

Joe Bishop

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Aug 21, 2015
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That sounds interesting and I will have to look that up. Some of my hunting partners were involved in wildcat cartridges.
 

Ken61

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Nov 6, 2008
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I'm simple. I find a factory round that is smaller than what I am working on. Look up the starting load with my preferred powder, set my Harrells powder measure to that load, size and prime some cases, go to the range with my bullet seater, and start with my low starting load and work up until I get where I think I want to be then start refining.
Be smart.
 

Ardon

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Oct 28, 2013
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Here's a link to the Powley Computer site. Please bear in mind that I haven't tried this site, just found it. Perhaps you could post your results from it to let us know how good/bad it is.

Here's a site for the Gordon's Reloading Tool. Same disclosure as above
Good luck and have fun with it all
 

nksmfamjp

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Jan 5, 2004
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QL has a function where you can design the cartridge then run the program to spit out pressure.

Cheers.
Isn’t that an add on software?

on the other side, it seems to get you close if you pick a cartridge of the same caliber and adjust the case volume and that ratio of overbore….
 

Equalizer

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Sep 19, 2019
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Gods country
Reading up on all the links. Thanks for the info. Extrapolating data from 358 Win start loads. I’m about half way through reading the powley site. Good stuff!!!
 

Hugnot

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Sep 26, 2020
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Montana
My wildcat's are AI types or have similar factory rounds. I go to the range with at least 60 primed, charged & sized cases, no bullets, each ID'd with charge weight using felt tip pen. I also have 24 plastic vials containing measured & ID'd charges. Start charges are at somewhat above above middle factory cartridge level for AI rounds & at start for similar rounds. Bullets, Lee Hand Press, Magnetospeed & other stuff go to the range.. Powder charges are weighed out in .5 grain increments having 3 to 6 of each. With luck I get it done in 1 session - almost always in 2. Lots of literature search before filling cases vials. Hoping that it won't be real windy or snow/rain at range.
 
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