Search found 1882 matches

by D_Hall
Sun Jul 26, 2020 1:30 am
Forum: Pneumatic Cannons
Topic: Calculations related to pneumatic cannon.
Replies: 9
Views: 1970

Re: Calculations related to pneumatic cannon.

Probably the quickest/easiest hand calcs you can do for potato gun prediction.... EndPressure = StartPressure * ChamberVolume / (ChamberVolume + BarrelVolume) MuzzleEnergy = (StartPressure + EndPressure) / 2 * BarrelLength * PI/4 * BarrelBoreDiameter^2 MuzzleVelocity = sqrt (2 * MuzzleEnergy / Proje...
by D_Hall
Mon Jul 20, 2020 11:09 am
Forum: Off-Topic Hobbies
Topic: I'm not photographer but....
Replies: 4
Views: 1244

Re: I'm not photographer but....

Setup wasn't anything fancy.

Canon T-6 (about a five year old consumer level DSLR).

Comet pic was taken with a 70-300 zoom lens at...maybe 100 mm.

Milkyway pic was taken with a fixed 50 mm lens.

Decent tripod.

Not star trackers or telescopes in the normal sense of the word.
by D_Hall
Mon Jul 20, 2020 12:53 am
Forum: Off-Topic Hobbies
Topic: I'm not photographer but....
Replies: 4
Views: 1244

I'm not photographer but....

...I'm still pretty pleased with these two pics I took tonight.

Image

Image
by D_Hall
Wed Jul 01, 2020 5:50 pm
Forum: Ammo & Parts
Topic: Brass as the foundation of a projectile?
Replies: 6
Views: 863

Brass as the foundation of a projectile?

I'm sitting here looking at a piece of 38 special brass. It just happens to be on my desk (yes, really). And I'm thinking to myself, "Self, this might make a good projectile." More to the point, I could see epoxying a nail in the primer pocket to make a dart. But a dart that is reasonably cheap/easy...
by D_Hall
Mon Jun 15, 2020 5:17 pm
Forum: Hybrid Cannons
Topic: Port size vs performance
Replies: 8
Views: 1047

Re: Port size vs performance

Some more thoughts on the thought experiment.... It assumes constant density, but this is obviously incorrect. But what DOES density do? In the first moments after the valve opens, not much. Constant density probably isn't a bad approximation. But as the projectile accelerates we know that pressure ...
by D_Hall
Fri Jun 12, 2020 2:36 pm
Forum: Hybrid Cannons
Topic: Port size vs performance
Replies: 8
Views: 1047

Re: Port size vs performance

The purist in me loves the idea of a port that is actually larger than the bore, with the breech tapering down such that flow into the bore is smoooooth and maximized. But yeah, the realist in me realizes that for the vast majority of cases this is beyond overkill. Hmmm... Let's see if I can come up...
by D_Hall
Sat May 30, 2020 5:26 pm
Forum: Off-Topic Hobbies
Topic: My current hobby: Cowboy Action Shooting
Replies: 12
Views: 3723

Re: My current hobby: Cowboy Action Shooting

Gun shot great. Had a lot of fun. Was stunned to NOT have the oldest gun at the range. One of the guys was shooting a .40-70 Trapdoor!

For all you folks who don't know old guns (not that I'm an expert)... Custard's men were using Trapdoors at Little Big Horn.
by D_Hall
Sat May 30, 2020 1:25 am
Forum: Off-Topic Hobbies
Topic: My current hobby: Cowboy Action Shooting
Replies: 12
Views: 3723

Re: My current hobby: Cowboy Action Shooting

Turns out that the same guys who run the Cowboy Shoots also do what they refer to as BAM shoots.... Bolt Action Military. Basically the idea is to use a bolt action military rifle in as-issued condition that dates to 1945 or earlier. It also turns out that my Mom once bought an 1895 Mauser on a whim...
by D_Hall
Sat May 02, 2020 10:01 pm
Forum: SpudFiles Discussion
Topic: GGDT and HGDT
Replies: 17
Views: 5368

Re: GGDT and HGDT

D_Hall, do you have any of the old documentation that went along with these? Or perhaps you or someone else is willing to help create some? Simple things about usage, running as an admin, the files that may need to be added, etc. I can certainly help here but don't want to reinvent the wheel if unn...
by D_Hall
Mon Apr 27, 2020 12:48 pm
Forum: Combustion Cannons
Topic: New member... my baby, Big Red
Replies: 15
Views: 2334

Re: New member... my baby, Big Red

KannonKing wrote:
Sat Apr 25, 2020 10:46 am
"pure oxygen" and fuel? Maybe you noticed the vacuum pump hidden in the battery box that evacuates the chamber before filling it with "pure oxygen and fuel".
If you're pulling a vacuum before injection, what *else* would you be using?
by D_Hall
Fri Mar 06, 2020 4:29 pm
Forum: Miniature Guns
Topic: Dual Camera System to enhance combustion weapons.
Replies: 13
Views: 4519

Re: Dual Camera System to enhance combustion weapons.

Yes, I found this topic a couple years late and it took me a bit to digest it.... ...But I don't think there's much to the "piling" phenom. It allows you to boost pressure, yes, but for a significantly smaller available volume in the combustion chamber. The result would be higher pressures, but decr...
by D_Hall
Thu Mar 05, 2020 10:55 pm
Forum: Miniature Guns
Topic: Dual Camera System to enhance combustion weapons.
Replies: 13
Views: 4519

Re: Dual Camera System to enhance combustion weapons.

[nevermind... hmmm... how does one delete a post with the new forum software?]
by D_Hall
Thu Feb 13, 2020 11:59 pm
Forum: Ammo & Parts
Topic: Low-friction/Specialty Ball Valves?
Replies: 11
Views: 2973

Re: Low-friction/Specialty Ball Valves?

You're not going to get much lower friction than teflon seals, but they can still be a bear to turn. Ball valves simply aren't designed for quick/easy motion.
by D_Hall
Mon Feb 10, 2020 1:40 am
Forum: Ammo & Parts
Topic: 3D printed golf ball dart tails (image attached)
Replies: 1
Views: 990

Re: 3D printed golf ball dart tails (image attached)

It will probably work, yes. But I think it's also a lot tougher than required. Put it this way... I've had decent luck with nothing more than a 2" deck screw. Drill a small hole into the ball. Screw the deck screw in. Done. Doesn't look nearly as cool, but it works.
by D_Hall
Sun Jan 26, 2020 1:09 pm
Forum: Ammo & Parts
Topic: They aren't cheap but...
Replies: 2
Views: 1296

Re: They aren't cheap but...

You'd need to build a sabot for them. At that point, you might as well build your own projectile (for less money).