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Flatland Crusoe
Jan 12, 2011

Great White Hunter
Master Race

Let me explain why I'm better than you


Doctor Grape Ape posted:

Could just make a second gas block with a large threaded hole on the top to give you access to the port. Once you find the right size hole then swap in the final GB.

Yeah this definitely independently came to mind for me.

I would approach it as doing simple proportional calculations. Running a computer simulation with CFD software if I had access to a student computer lab. And ultimately just using those numbers to start small and open it up on the prototype. I'm not super familiar with AK's but I am a MechE PE and that's how I would do it. I have a friend from school who is an engineer in the firearms industry and a lot of what they do with designing on existing platforms involves a lot trial and error plus mag dumping for reliability statistics.

Flatland Crusoe fucked around with this message at 14:36 on Dec 24, 2016

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Flatland Crusoe
Jan 12, 2011

Great White Hunter
Master Race

Let me explain why I'm better than you


shalafi4 posted:

Check out the effort post towards the bottom of the last page. There's a bunch of handwaving involved but that's what I walk through. Honestly as simple as the proportion calculations are I should just setup a spreadsheet to calculate ranges of them.

No I saw those calcs but I'm saying that my experience is that hand calcs are going to get you an order or magnitude calculation compared to needing a 3mm vs 4mm hole and that any sort of more complex modeling is both easier and more accurate. Hand calcs tend to minimize variables a lot of little variables that add up to mattering a lot when talking about expanding gases and varying combustion rates that need to then expand around (2) 90 degree corners. The surface of the barrel and the clean of the gas hole are going to net different results that saying clean 4140 steel into a hole that has a less that perfect radius (or lack there of) because those things affect pressure and flow of gases which will be dynamic during the acceleration of the gas piston.

A great example would the physics of motion used in classical physics vs control systems where acceleration includes the inertia of rotation and acceleration rate and air resistance or large multiple variable equations.

Fluid dynamics which you are dealing with combustion of powder really are much better at a small level using computer simulations than hand calcs.

At the end of the day you are going to play around with the hole size unless you pour the resources of nasa at the issue.

It's one of those issues where I calculate the spring size I think I need and then order 2 sizes harder and weaker to try in addition to exactly what I think I need.

Flatland Crusoe
Jan 12, 2011

Great White Hunter
Master Race

Let me explain why I'm better than you


As much as anything I'm telling you applied engineering largely revolves around adapting known or similar solutions (often in unrelated applications) rather that what engineering professors drill into your head in trying to learn to derive everything from scratch basic equations. Quick load or similar software would probably be the most useful if you are using different powders or situations.

People spend whole careers learning the nuances of specific systems and tapping that knowledge versus deriving the theory of everything is much more efficient and also has more simplified ratios and assumptions. I'm usually going to make machine design decisions based on manufacturers literature instead of rereading Shigley's machine design.

In the case of a drilled hole it's easier to make a hole bigger than smaller. So start on the side of undergassed and work up. Cartridge pressure, powder volume and barrel cross sectional area are the only variables I would consider not to be held constant.

Flatland Crusoe
Jan 12, 2011

Great White Hunter
Master Race

Let me explain why I'm better than you


Shaocaholica posted:

Why not just make the hole towards the big end of hole sizes and make your gas block adjustable? If you're going to be loving around with different loads and barrel lengths and suppressors anyway.

Because in the long run over gassed semiautos break stocks and batter receivers.

If you are going to sell the barrels optimizing the gas port should be a thing you have figured out at least to some extent.

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