Developing a 50 Cal. Airgun Barrel

50 Cal. Airgun Barrel - Why 50 Caliber

(edited for content, Nov. 20, 2009)
I have been fascinated with big bore airguns for awhile. Trouble with airgun barrels are that
to get a commercial pipe close to the size of a commercially available caliber diameter is
near impossible. Over the course of the last two years I have been in contact with Clarkarms.
Mr. Clark provided me with a manufacturer and size of pipe that was perfect. Well I found a
supplier but I didn't get what I specified and was sent a different manufacturer of pipe. The size
tolerance wasn't near where it should have been, so I was stuck with two lengths of pipe that
I couldn't use for 50 Cal barrel. Bore was .499" and would have have been much to loose for the
inside bore. On top of this I had spend $300+ dollars for something I couldn't use.

I left the project for awhile as I didn't have time. Plus no real place to work. Had some family
issues early this year which forced me to find work elsewhere, but things have since improved and
I can now continue on some projects related to airguns.

Experiments - Creating 50 Cal. Airgun Barrel

November 14, 2009

As mentioned above the pipe came in the correct outside diameter, but inside bore
was .498, .499". As the pictures below will show, I was able to bring the pipe down
to .492, 493" inside bore diameter which will now allow it to be sized to the
bore to .495, .496".

I created a tool that allows me to shrink the pipe.

Having the swagging (shrinking) tool complete, my dad suggested I try on a short length
of stainless pipe, before I setup to do a full barrel length pipe. I pushed the stainless
pipe through the tool opening. I checked the size and firstly, I was amazed at
how smooth and uniform the size had become on the stainless pipe. The smoothness shows
up a little on the pictures. I think a buffing wheel is all that would be required
after to brighten the stainless.

Having success, my dad and I setup to do a full length. I didn't bother setting
up for straightness but simply wanted to try shrinking the pipe. We mounted the
pipe and shrunk it. The process worked so well and stays very uniform if you do
not stop the process. Now because the pipe wasn't supported some rings
were developing as it was swinging about while the pipe was being shrunk. You will
see the rings that developed in some of the photos.

Also, you will see the before and after sizes of the pipe. My next step is going to
be to improve the system to ensure better support, level, straightness. This will
allow the pipe to be as straight as possible to hopefully keep it straight. Before I left
my dad's shop I checked the hardness. A pipe not "swagged" didn't show up on the
rockwell C scale on the hardness tester. A pipe that I had swagged showed 10
rockwell C. The stainless barrel had work harden some.

From here I can now size the inside bore and finally button rifle. Timing is just
before December and will see how much I get done before year is over.

Pictures of 50 Cal Stainless Pipe Sizing

Stainless pipe as received from supplier.

Stainless pipe after sizing compared to rough finish.

Finish compared, rough, emery cloth, and sized. Sizes ID before.

Long pipe ID ends sizes compared. Very uniform with size.

Longer pipe rib marks occured causing pipe to curve.

~ thanks for reading, comments, questions?
Email me: ~ Pedro

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