4 bore barrel balance

[44-henry]

The problem with the proofing load is that when it is done you generally have no idea of the damage that might have been done during the proof. I prefer the proofing method suggested by Brockway where the barrel is proofed four times. The first two is with a double charge of powder and one ball, the last two is with a normal charge of powder and two ball, thus duplicating the two most common mistakes made in loading. Even with this I would suggest caution, since really, it is all just a crap shoot. The barrel might withstand four such firings, but who's to say it doesn't suffer internal damage during those first four shots that will cause it to fail on the fifth. Barrels made by reputable makers and within industry standards don't cause me much concern here, because I do have faith in their construction. Yours, on the other hand, would constantly ring pipe bomb in my mind.

You have received a lot of good advice about your project by some extremely well established and respected people in this business, if I were you I would heed that advice and buy a suitable barrel for your project, there are people who will make you a safe and much more authentic 4 bore barrel if you feel you have to have one.

 

[Zonie]

Many parts that go into jet engines are proof tested. Especially those that are subjected to high pressures and high speeds.
Those parts that are pressure tested are subjected to pressures that greatly exceed their operating pressures, just like barrel proof tests however there is one big difference between what the engine manufactures do and what is done by folks who build guns for a hobby.
After the parts are tested, they are always inspected to see if any flaws have been uncovered or caused by the high pressures.

On non magnetic parts, this testing is done using Fluorescent Penetrant Inspection. If the part is magnetic the test uses Magnetic Particle Inspection. Occasionally X-ray or eddy current tests are also done.

If I were going to proof test a barrel, I would have at least one of these tests done to it after doing the proof testing. After all, subjecting a part to high stresses does weaken the part.

Magnetic Particle and Fluorescent Penetrant testing can be done by shops that rebuild car engines. Most of the really good shops have the proper equipment and will do the tests for a reasonable amount of money. Especially if the shop is owned by someone that likes guns.