The Craftmans Shop > Backyard Ballistics

Building a PCP airgun.

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David Jupp:
One thing to be very much aware of if using Aluminium and its alloys - no matter how low the stresses are, fatigue will be an issue so the item will have a finite life (determining what that might be may not be simple).  Unlike steel which shows a 'knee' in the S-N curve, Aluminium does not have a limiting stress below which fatigue will not occur.

Jonny:
Quite right David and why Airstream above wont use aluminium for pressure vessels.
I have returned and now on my third complaint to a well known German manufacturer using aluminium for the cylinders. Thats 6 i have come across, two brand new and one recall with visual cracks. Think they are listening this time, but has took then 5 years to do so with their typical we know better attitude.

Its not entirely the strength of the tube, its the end plugs and how they are fitted that seems to go amiss.
There are plenty of very iffy production rifles around that have 232 bar slapped in them, i wouldnt put 70bar in.

David Jupp:
Aluminium Dive Cylinders have additional checks on the threads where the valve screws in at each routine inspection.  For steel cylinders a visual on the threads and check with go/no-go gauge is adequate, for Aluminium this is supplemented by Magnaflux examination to pick up cracking which is a known issue.

tjensen:
Nice work.
2 questions:
1. Book about it?
2. Bulgarian barrels?
Thanks :)

NeoTech:
There was a book in circulation that is hard to get hold off these days. The author published it by himself, its basicly a guide to build PCP airrifles.

And yeah, now adays bulgaria is not the prime source slovenia is.. check royal.si for cheap rifles that can be stripped for necessary hard to find items you can't make your self.
Pay attention to your local laws beforehand tho. Might be illegal where you live.

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