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CaptainSlug

Member Since 17 Feb 2006
Offline Last Active Today, 04:48 PM

Posts I've Made

In Topic: On the topic of SCAR barrels

04 December 2017 - 10:36 AM

No, the strings work better for every type of dart so long as you adjust it, test, adjust it again, test again. Until you find the setting that works for that particular dart.

 

The device without strings was to show that I can get a positive result without strings, and without any twist in the design. I managed to accomplish that with one of the designs, but not the other.

 

The spiral hole pattern that is commonly used for paintball to accomplish the same effect probably didn't work because it's not a good surface to print. It would probably work fine as a machined feature, and that reflects some testing torukmakto4 did two years ago with looooong barrels with porting near the end.


In Topic: Caliburn: Mag-fed Pump-action Springer

04 December 2017 - 08:48 AM

I have a caliburn-specific SCAR barrel up on Thingiverse now.

 

299c1cca9e05fd91820cd38392b311e8_preview

https://www.thingive...m/thing:2686643

 

Uses 0.25mm fishing line.

 

The file set includes a little nib you can glue onto the end of a 1/16" diameter weld rod in order to make a noosing wand to help string the SCAR barrel.


In Topic: Plunger tube shape significance?

01 December 2017 - 07:53 AM

1. Check out any of the "HAMP" links in the homemades directory

 

2. Correct

 

3. Spring Plunger performance is dependent upon how fast the plunger can accelerate. This acceleration gets translated into a short burst of pressure. Heavier plunger heads take more time for the spring to get moving, so you need to keep the mass of the plunger to a minimum.


In Topic: Looking for Wars to attend in WV

30 November 2017 - 11:22 PM

Everything from stock to homemades will be used.


In Topic: Plunger tube shape significance?

30 November 2017 - 02:45 PM

There is a friction, restriction, mass, and velocity issue when scaling upwards in plunger diameter.

 

1. The larger the ID of the plunger tube, the more friction the seal has. So you have to transition to atypical seal types that are much lower friction. KaneTheMediocre's solution of using yarn is clever and meets this criteria perfectly.

2. The ID of the barrel is a source of restriction with being able to pump a higher volume ratio of air quickly. The end of the plunger tube being a huge ratio of area transition can throttle plunger velocity since it starts to starve. You scale plunger diameter up more readily when the bore diameter is also scaling up.

3. The larger the plunger head gets, the more mass it has. The more mass it has, the harder it is for a spring of a certain load to accelerate it. So you end up having to scale the spring load to match.

4. There's a trade-off and a dynamic relationship between how fast you can get the plunger going, and how much volume it has to work with in the time frame in which it is accelerating. If you lower the velocity, you lower the potential peak impulse of pressure that the plunger can reach. This pressure impulse determines what pressure level the plunger can reach even in the event of there being leaks present. And you basically have to think of the dart as being a slow leak.