Saturday, July 26, 2014

Shhhhhhhhhh !

A few months ago, I started a project to build a device that would allow me to test fire loads in the back yard without the neighbors thinking I was blasting stumps or something.  Like most of my projects, I shelved it for work or other projects that caught my fancy.   I picked it up again today and boy am I pleased with the results!

I read somewhere that people were using gas bottles for this purpose.   Whatever I read didn't give any details.  It just sounded like they'd unscrew the valve, stick the gun's muzzle in the hole and blast away.  I wasn't really comfortable with that because I've seen what a 30-06 can do to a piece of steel even when its angled at 45 degrees and I just couldn't see how the bottom end of the bottle could take rifle fire for very long.  Its probably an inch thick but even that would give way pretty quickly if it had to stop rifle bullets.

By comparison to just unscrewing the valve,  my solution was overly complex and much more difficult and costly to manufacture.  I simplified it quite a bit today.

The first concept was something that I would shoot through.   To manage that, I cut about three inches off the  bottom end of the bottle to give me access to the cylinder's interior so I could install my ingenious muffler and baffle system.   I  bored a hole in the center of the piece that I cut off to allow the bullets to pass through.   The idea was to install the innards and then reattach the bottom using a thick gasket and a series of turnbuckles to snug it all up. 

I finally ditched the whole idea of keeping the bottom piece in the plans and decided to just let it go commando because I just couldn't see how I'd be able to line up the gun barrel consistently enough to get the bullet through the hole in the far end every time. 

The resulting components looked like this.

The innards were selected via strict scientific parameters for performance and durability, and because I already had them lying around in the shed.  The baffles are made of poplar and the muffler is a Thrush glass pack that spent about one weekend on Ruth, the Jeep.

 The baffles go on each end of the muffler and the whole works goes inside the cylinder.  Then the open end of the bottle gets slammed into the dirt mound.  The shootin' end is supported by an old transmission housing - again courtesy of good old Ruth.  I did say I simplified it.

This was a temporary setup to test whether the concept would work so I didn't spend a lot of time building a permanent version just to find out that it didn't.  The shootin' hole is still threaded for the valve too so I had to be extra careful with the rifle barrel during testing.

The rifle is a Cooper Model 38 in 22 Cooper Centerfire Magnum.  Less than a 22 Hornet but more than a 22 Winchester Magnum Rimfire.  I chose it for the testing because I didn't see any sense in starting out with something huge in case the project would work on a small cartridge but be overtaxed by a big one.  I also chose it because its barrel would fit the opening in the bottle and it's the rifle that drove me to building this whole setup in the first place.

I have a problem loading the ammo.   Even with a starting load and the exact bullets called for in the data, when I seat the bullet it compresses the heck out of the powder.  Several things happen.  Since the brass is incredibly thin, the brass expands and lets go of the bullet.  Sometimes the bullet cocks to one side and the round won't chamber.  The bullet also creeps out far enough to interfere with feeding from the magazine and with chambering the round. 

22 CCM loading data is rather sparse and I want to go with a powder that is a tad quicker than the WW 296 that I love so dearly so I need to be able to work up a load on my own.  Can't work up a load without test firing.   Don't want to frighten the neighbors either so its drive 30 minutes to the river,  drive an hour to the range or build something to contain the sound.

I put electrical tape on the barrel to protect the finish.  The fatter portion with the tape on it has a thin slice of cork under the tape to act as a gasket.  The barrel slides into the shootin' hole far enough that the muzzle is actually inside the cherry bomb muffler and the cork protects the barrel and makes a seal.

I said I was pleased with the results.   When I fired the rifle, the sound was barely audible.  My feet crushing the damp leaves made more noise than the shot did.   It was more of a "poof" than a "pop" or a "bang."  I couldn't believe it.

I opened the bolt and out came the empty case.  I held the muzzle upright and shook the rifle expecting unburnt powder to come out.  Nothing did.  I looked down the barrel and saw light.  I still couldn't reconcile the lack of sound with the thing actually having fired so I ran a cleaning rod through the barrel just to make extra sure.  Sure enough, it came out the breech without having to push anything out of the way.    I tested it again and got the same results. 

This could be as big or even bigger than my portable reloading setup.

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