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Spudder's Design Tool
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Version:0.2aReleased:10/17/2025
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BackgroundTwentyish years ago I created the GGDT/HGDT codes to model pneumatic and hybrid spud guns respectively. The codes were well received and worked reasonably well but there was a problem: The codes were written in VB6; a language that was obsolete almost as soon as the codes were completed. While a dedicated nerd can figure out how to make the old codes run on a modern Windows machine, this does not help IOS or Linux users. And yeah, it takes more work than it should even on Windows machines. Thus I endeavored to create a spreadsheet to replace the old GGDT/HGDT codes in a (comparatively) portable format.
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My understanding of compressible fluid flow has improved in the years since GGDT/HGDT were written and this spreadsheet should reflect my better understanding of the topic. In the same breath, some features of the old code - while technically more accurate - didn't seem to make much difference on overall gun performance. These features were omitted from the spreadsheet.
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On the topic of omitted features, the list of valve options in the new code is greatly reduced. This was done due to my understanding that very few people were using valves other than burst disks or pilot/piston valves. If this is incorrect, I would appreciate the feedback. Additional valves can be added back in, I just didn't see the point if nobody uses the other valves (but maybe I'm wrong on that front). Similarly, the modeling of pilot valves was greatly simplified. For a properly designed valve, this shouldn't make much difference but not all valves are properly designed. Should I fix this? Again... Feedback is appreciated.
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DescriptionThe spreadsheet consists of four pages (five, if you want to include this page).
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Main - This is the primary user interface for the gun design and performance. All unit systems and gun design are defined on this page and basic performance is summarized.
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Mix - This page is a quick and easy to use fueling calculator for hybrid and simple combustion guns.
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Exterior - A very crude exterior ballistics predictor. Emphasis on the word "crude".
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Interior - The sheet that does the interior ballistics (performance prediction). Most users will never need to open this page but it is available for the gun geek with questions.
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UseageUseage of the spreadsheet should be largely self explanatory, but just in case….
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1 - FIRST selected the Main page and select the units you prefer working in. From there, it is as simple as filling in all the required parameters. The Main page includes a brief description of each required input.
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2 - If desired, external ballistics can be studied on the Exterior page. There is an option to use muzzle conditions defined by the Main page (automatic), or to enter the parameters in by hand (manual). Beyond that, the inputs should be largely self explanatory.
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3 - A loading calculator for combustion and hybrid guns. It produces data for both manometric loading and metering pipe loading.
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That's it! The only catch that may not be obvious are my box formatting choices. Orange with a black background…
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LIKE THIS
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…indicates that this is a block for user input. A gray background with orange letters…
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LIKE THIS
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…indicates that this is a block for spreadsheet output of significant interest.
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Changes Since 0.1d
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* Added support for CO2 and helium powered cold-gas guns
* Added support for MAPP powered hot-gas guns
* Small changes to user interface due to the above changes
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