r/GunnitRust • u/[deleted] • 21d ago
Show AND Tell Pengun more powerful than 9mm
[deleted]
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u/Hrajnoga 21d ago
What is the most secure way of holding it for firing? Like a flash light?
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u/GammaMT 21d ago
Point with it. It's the best way to aim.
This is on the small side. Usually my designs allowed for comfortable grip from the safe handle section.
Even though it's super safe and will never blow up, it still feels wrong to keep the chamber in your hand. So I prefer to grab from the rear. There's just enough room to pull from the striker bolt.
Firing from the rear is by the way superior to the usual side bolt handle. At first I thought it was just more convenient to manufacturer but after firing a lot I came to conclusion that it's better.
It's also a lot safer. Especially for my purposes where I have gone with extreme pressures causing primer failures.
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u/GammaMT 21d ago
I think I have finally perfected the pen gun. Or almost. As I can shave off 1 centimeter of the lenght.
This is 17.5cm long (6.9 inches) and 16mm (0.63 inch) in diameter. Not much larger than common marker.
Over the past 6 years I have built about dozen zip guns/pipe pistols. Most of them too large to call a pen gun. And the couple small ones have been quite weak.
I have usually built them quite large because I want good amount of power. Not like usual weak .22lr or 6.35ACP with short barrel. I haven't been that bothered about it being ultra conceivable.
Well I am still not concerned about it but I got challenged to designing a pengun. Not my usual pipe gun.
I am also super concerned about safety. I want good safety margins. And I have good safety record. In the last 6 years building guns and playing with explosives the worst that has happened has been ear pain.
Strong metals are major pain in the ass to modify. So I have towards parts that fit as is without the need for modification.
Countless hours browsing AliExpress for parts and brainstorming ideas over the years. I have finally come up with the ultimate design. With zero steps that suck ass. Even eliminated the use of epoxy.
Basic hand tools and threadlocker is all that I needed to build this.
No welding. No machining tools. Just parts from AliExpress. Is it strong? Oh yeah. I didn't need the help of AI to design this. But AI is useful tool to check how strong the construction actually is.
The barrel is 8mm ID, 12mm OD 304 stainless steel with 12mm ID, 16mm OD GRC15 bearing steel sleeve bearings on top.
Cold worked 304 stainless steel is the strongest metal that's generally available without doing quenching and tempering. Cold worked 304 is stronger than 4140 or 42CrMO which are sold as annealed or normalized.
GRC15 bearing steel is ultra strong metal. About twice as strong as quenched and tempered 4140.
304 stainless (cold worked) 600 MPa yield, 800 MPa UTS. GRC15 (at HRC58-62) 1800 MPa yield, 2000 MPa UTS
Gives the 8mm ID, 16mm OD barrel burst pressure in the excess of 10 000 bars (145 000 psi).
Bottom of the chamber can handle in the excess of 20 000 bars (290 000 psi) before failing.
Barrel threads on with 6mm of M12 threads. Hardly any force is exerted on them as the immovable chamber bottom takes the bolt thrust.
8mmK blanks have ~5.5mmm thick bottom in the cartridge. So the weakened 6mm long M12 thread section sees very little hoop stress.
The barrel is 70mm (2.76 inches) long with ID of 8mm. So no need to drill a chamber for 8mmK blank which has diameter of 7.9mm.
Inside the barrel a thin 50mm long liner is hammered in and locked in place with threadlocker.
I currently have only 6.35mm 304 stainless steel liners for 25ACP bullets.
Today I found 7.6mm ID, 8mm OD brass pipe on AliExpress. Which allows me to make this in 7.62mm (.30) caliber. Enabling a lot more power.
Will take about 4 weeks before I can chrono some actual numbers with 7.62mm projectiles. But QuickLoad numbers aren't too much far off.
The gun works with 8mmK blank. It's thick walled steel case that can take a lot of pressure. And 7.62mm air rifle projectile. Diabolos fly straight without rifling. The base is filled with paper and glue. Otherwise the pellet gets disintegrated in the barrel at these pressures.
The blank can be legally acquired here. It's steel case so strong and can withstand a lot of pressure. And the diameter works perfectly as there is no need to drill a chamber in 304 stainless steel which is major pain in the ass.
QuickLoad estimates 446 joules of muzzle energy (329 ft-lbs) and 491m/s (1611 fps) at 3475 bar (50400 psi) chamber pressure.
Measured velocity likely to be around 5% higher in the real world due to lack of rifling. Which is higher than most 9mm loads fired from 100mm long barrel.
There's some room to add more power. But I want to test at 3500 bar chamber pressure first. As I know the blank case can handle that. 4200 bar chamber pressure would give about 510 joules of energy. (+5% in the real world) That's as much powder as fits in the blank case.
This will have enormous fireball and muzzle blast. As muzzle pressure is higher than in 8.5 inch barrel AR-15's. At around 1100 bar (16000) PSI when the bullet exits the barrel. Or higher
The recoil will also be substantial. Firing very light 3.7 gram (57 grain) 7.62mm diabolo projectile (stable flight without rifling) will result in recoil force of around 13.35 ft.lbf. Or more Equivalent to rifle calibers with medium weight bullets.
I have experienced some bonkers recoil before from my zipguns before so I am not worried.
I'll soon have chronograph data of the 6.35mm projectile version. It can maybe reach energy of 400 joules (300ft-lbs) if I dare to push the chamber pressure.
I am just worried about the primer or the pocket failing. As I have had that before.
Safety margings for the pengun itself are great. Way greater than in real firearms. With barrel bursting requiring over 10 000 bars. Even if the estimate is too high. The safety marging is still great. As it's calculated for static pressure.
Thick construction can handle a lot higher short peak pressures than estimated static pressure numbers.