barrel

[John Taylor]

So I was thinking I might like to build an air rifle and I have an extra .58 cal. barrel on the shelf. Need to see some drawings on the valve system. Also I would like to let everyone know that T.J.'s is making barrels for the air gun crowd.

[NoZombies]

John, based on the examples I've seen of your work, I'm sure it would be quite a nice piece. I look forward to seeing how this develops!

[Pakprotector]

Maybe somebody can take on a 750 yard pop can shot with this one... you're looking at what, 600 gr ammo?

Some interesting stuff on hammer weight: http://www.gatewaytoairguns.org/GTA/...?topic=53185.0
cheers,
Douglas

[W.R.Buchanan]

John; We all want to see drawings of the valves. I have seen some of the old simple ones which are nothing but a poppet valve that gets hit by a hammer.

The new ones for these big caliber guns are closely guarded secrets. If they weren't there would be a lot of big guns on the market and as you know there aren't a lot of big guns on the market.

As caliber goes up air usage goes up exponentially. The Quackenbush .50 cal. guns get 2 shots per fill. If the valve doesn't work right you only get one.

Randy

[MT Chambers]

The op certainly knows his stuff, but the limitation of 1 or 2 shots between fills, makes it a benchgun only, I know some will say "well I only need 1 shot" but when your first or even second shot wounds an animal, what then? let the animal/bird suffer? Sorry but an airgun that can't be used in town, or in the back yard, or out in the bush is a non starter for me. Don't get me wrong, I'd love to see anything that the esteemed op comes up with!!!

[John Taylor]

There are lots of thought on air guns and I have talked about a few with customers. One idea is using OX and a drop of diesel. This one would need to be tested from a distance, I have seen the damage a drop of oil can make when OX is applied.
I had a Crossman air pistol with a total release air chamber, no hammer. Was thinking along these line and adding another large chamber with a valve between the large and small chamber. I'm in the proses of making a pellet mold for a .62 caliber for a customer , might be fun in his muzzle loader.
All I need is more hours in a day so I can put some of my thoughts to work.

[W.R.Buchanan]

John: the diesel idea was done by Weihrauch 40 years ago. The gun, which was a .22 caliber HW35, had an attachment that dropped a drop of Ether into the compression chamber. The heat generated by the compression that takes place as the piston drops caused the ether to ignite and velocities were in the low 1400 fps range with normal 16gr .22 cal. pellets. Breech seals were a problem due to the higher pressures generated.

The gun was known as the Barracuda and is one of the most sought after German Air Rifles ever made. Nobody with a brain gives one away they are worth a bunch.

Unfortunately this same concept will not work on a PCP since the air is already compressed and when released cools instead of heating, so the fuel can't be ignited.

Randy

[John Taylor]

John:


Unfortunately this same concept will not work on a PCP since the air is already compressed and when released cools instead of heating, so the fuel can't be ignited.

Randy

If I remember my diesel training, the 6-71 GM has 425 PSI compression that generates about 450 degrees. If 1,000 psi or more is dumped into a small chamber with a little diesel at the same time it most likely will ignite. If it is OX it will have a complete burn. Saw what happens when a pressure gauge was changed on an OX bottle and the rebuilt gauged had been calibrated with oil. The man who changed it out is no longer with us. That would be the reason for test firing from a safe distance.

[Pakprotector]

build a shock tube, and then a wee bit of graphite behind the boolit( or packed in the tail ) will get lit. So to say a small, tuned, intermediate chamber.
cheers,
Douglas

[W.R.Buchanan]

John: the air must be hotter than the flash point of the fuel to ignite it.

Compressed air when released is cold.

Go let some air out of a tire, and see if it is hot or cold. If you need more pressure go crack the valve on and oxygen cylinder and see if is hot or cold.

I assure you it will be cold, and the higher the pressure the colder it will get when released.

Not speculating here, been around this stuff my entire life, wouldn't lie to you..

Air gets hot when compressed, and compressed air gets cold when released.

Early Benjamin and Sheridan Air Rifles had brass barrels so that the condensation on the inside and outside of the barrels from the released air wouldn't rust them.

A Blower on an engine is compressing the air, and it is also heating the air. Mickey Thompson had a dragster that was banned from competition because it used compressed air in bottles instead of a supercharger. The engine made over 3000 hp. in the 60's due to the fact that the cold air did not induce detonation like the hot air from a blower does.

They are over 8000hp now and still fighting the same problem with Detonation. The engines are just stronger and can take more of it now. They still blow up, and when they do it gets pretty spectacular.

Randy

[John Taylor]

John: the air must be hotter than the flash point of the fuel to ignite it.

Compressed air when released is cold.

Go let some air out of a tire, and see if it is hot or cold. If you need more pressure go crack the valve on and oxygen cylinder and see if is hot or cold.

I assure you it will be cold, and the higher the pressure the colder it will get when released.

Not speculating here, been around this stuff my entire life, wouldn't lie to you..

Air gets hot when compressed, and compressed air gets cold when released.

Early Benjamin and Sheridan Air Rifles had brass barrels so that the condensation on the inside and outside of the barrels from the released air wouldn't rust them.

A Blower on an engine is compressing the air, and it is also heating the air. Mickey Thompson had a dragster that was banned from competition because it used compressed air in bottles instead of a supercharger. The engine made over 3000 hp. in the 60's due to the fact that the cold air did not induce detonation like the hot air from a blower does.

They are over 8000hp now and still fighting the same problem with Detonation. The engines are just stronger and can take more of it now. They still blow up, and when they do it gets pretty spectacular.

Randy

For the same reason the OX gauge blew up when the valve was opened. You are letting compressed air into a sealed area which builds up the pressure in that area very quickly until the bullet starts to move. You are correct about the temp going down when pressure is released ( think air conditioner) but this is not releasing the pressure until the bullet starts to move. It is raising the pressure in a small confined area. I worked on a diesel engine that used compressed air to start, if the air was cooling when it went into the cylinders the engine would never start.

[Multigunner]

John: the diesel idea was done by Weihrauch 40 years ago. The gun, which was a .22 caliber HW35, had an attachment that dropped a drop of Ether into the compression chamber. The heat generated by the compression that takes place as the piston drops caused the ether to ignite and velocities were in the low 1400 fps range with normal 16gr .22 cal. pellets. Breech seals were a problem due to the higher pressures generated.

The gun was known as the Barracuda and is one of the most sought after German Air Rifles ever made. Nobody with a brain gives one away they are worth a bunch.

Unfortunately this same concept will not work on a PCP since the air is already compressed and when released cools instead of heating, so the fuel can't be ignited.

Randy

First I heard of a piston airgun altered specifically for dieseling was that after WW2 Germans who needed small game to supplement their groceries and weren't allowed cartridge arms for whatever reason would alter the rifle to squirt a spitz of wood alcohol into the cylinder just as the trigger was pulled. Apparently some gunsmith figured this out and did the alterations on the sly.

I've used a squirt of cigarette lighter fluid down the bore of a Crosman M1 carbine piston BB gun before cocking. These are push in barrel cockers. Their was a small but sharp report and greatly increased velocity. with a bit of smoke curling out of the muzzle.

As for barrels, I wonder if the Lancaster Oval Bore has ever been adapted to air guns. Seems to me it would be near friction free with only the skirt of a waisted pellet expanding to take the spin. Much easier to keep clean as well. The skirt would suffer no mutilation from contact with lands and sealing should be more effective.
If a tighter fitting bullet were used a bolt with good seating leverage could be used to pre engrave the bullet.

[W.R.Buchanan]

John: first, it is only equalizing the pressure between the tank and the space provided it is not compressing anything, and as the pellet travels down the bore the pressure drops.

Second the OX Reg blew up due to a hole in the diaphragm just like a balloon pops. However good regulators (Victor) are made to take this. Seen many do this since I worked construction for many years. They were taken to the Welding Supply Store and rebuilt. No one with a brain puts oil on an O2 regulator especially if they can read where it says to "use no oil" on the regulator itself.

Third: that diesel engine that used compressed air to start was directing the air to the cylinder that was on the power stroke. The next cylinder that was on the compression stroke was the one that fired and started the engine. Other diesels engines like Detroit Diesels, use an Air Powered Starter motor.


Go ahead and try your theory out. If it actually works I will be happy to eat my words. All you have to do to test this theory is to put a drop of diesel or whatever on a small pill of cotton and place it behind the pellet in a Sheridan or Benjamin pump up gun or a PCP gun if you have access to one. If it is going to work you will know as soon as you pull the trigger.

However if it was going to work don't you think some airgun smith would have tried it by now? Especially with the proliferation of big bore air guns made with the intention of hunting big game.

Do Chrono the results before and after. And like I said, I WILL eat my words if you are successful.

Definition of success: A significant increase in velocity, like doubling it.

Even the Weihrauch Barracuda used "ether" instead of oil and the reason was the low flash point. There wasn't enough heat to reliabily ignite Diesel or any kind of heavier oil. If there had been, the results would have been much more dramatic due to the higher BTU content of the oils over the ether.

WE also would have seen a completely different type of firearm on the market.

Please do not take any of this as any kind of insult. We are having a friendly discussion, and nothing more..

Randy

My Cummins powered Jeep.