A rifle action's strength -- what's the current test method?

[Dave DeLaurant]

NOTE: the title should read 'soundness' instead of 'strength' -- my bad!

Recent threads on known problems with 03 Springfield and US Krag receivers have been very informative. It is useful to know that some rifles are stronger than others, that certain actions have inherent weaknesses and known production defects.

That still leaves a related question unanswered: what is the best test method for finding critical weakness in a specific old rifle?

To this day, the proof house method of firing a deliberately overloaded charge is a standard test for soundness in many countries: https://www.gunmakers.org.uk/the-proof-house/

I suppose this process has some merit, especially with new-production arms. However, a flawed bolt or receiver might survive a dozen overcharges before exhibiting a hidden defect that can result in a catastrophic failure sometime later in the course of regular shooting. Read Bob Bell's piece in the 1997 Gun Digest, When a Rifle Blows.

When I was a kid in high school, I used to get a lift with my dad and arrived about an hour early for my first class. I would kill time by going to the school library and reading old issues of American Rifleman from the 1960s and 70s; back then, the Magnaflux NDT process was SOP for detecting flaws in rifle bolts and actions. Here is a description of the process by a present-day user: https://atrona.com/mpi-testing.html

You don't hear Magnaflux mentioned around the shooting campfire much these days, or at least I haven't. Any of you know whether it is still considered state of the art for evaluating old guns for flaws? Who offers the service to the gun collecting/shooting community? Is there something better available today?

Fire damage to heat treatment is invisible after refinishing. Anyone know of a reliable test for this? A few proof loads, maybe?


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FWIW, when it comes to old MilSurps I'll admit to being a cowardly wuss. I prefer to shoot all of my bolt action MilSurps at reduced ranges with reduced pressure handloads and cast lead or plated bullets. It's easier on the gun and makes service rifles much more pleasant to shoot -- the Steyr M95 Stuzen, in particular, is a delight to shoot when downloaded.

 

[Nature Boy]

If you have access to P.O. Ackley’s books, he did a lot of testing on various action strengths by overloading them and observing what failed first.

it’s an interesting read

 

[entropy]

I don't claim to speak for gun manufacturers, but I'd suspect there are formulae backed by over 100 years of testing for the various types metals used for receivers. I. E. 4140 can take x0,000 cup or psi, 7076T3 can take x0,000, etc. This gives them direction to start from, I would HOPE they physically proof test them also.

 

[ApacheCoTodd]

Two simple and cheap ways I use from time to time are brake cleaner and/or an electrolysis setup.

NOTE: I am NOT saying this is fool-proof!!!!!!!!!!!!

For the brake cleaner, I soak the suspected item in clean, warmed motor oil. Wipe it down for the excess surface oil but I don't worry too much about it. Spray the item with brake cleaner and watch closely for any oil that might have been soaked into an imperfection to wick out well after the rest of the surface has dried of brake cleaner. If you do this with carburetor cleaner the oil will sometimes push a white line of the dried carb-cleaner along as it wicks out - further outlining a potential flaw.

The downside with carb cleaner is it contains residual ingredients and evaporates considerably more slowly than brake cleaner but it's the residue that helps highlight flaws in some cases.

Ironically, I always clean off the carb cleaner with brake cleaner.

The other is to use a very clean solution in an electrolysis bucket and with good lighting, watch the part for signs of the gas-bubbles inexplicably forming on an otherwise smooth - not corroded - area and then examine that area more closely.

As far as Maganflux/MPI(Magnetic Particle Inspection) and NDT (Non-Destructive Testing), they are still common and in many cases mandatory in both wet and dry procedures.

Todd.

 

[Llama Bob]

There have been some good suggestions (especially reading the PO Ackley books as they answer correctly what many on the internet like to speculate incorrectly about) but I would also add to get an accurate diagram for the parts in question, and measure things. While cracks/imperfections have doomed some rifles, bolt setback and resulting excess head space has doomed MANY more. For a rifle you have any concerns about a no-go gauge at about $30 well worth the investment. That way you can check for excessive headspace after every session if desired.

 

[MZ5]

Let me make sure I understand the question, because I see two divergent lines of thought in the responses thus far.

Are you asking:

A) How to determine whether a _model_ of gun, or at least a _production lot_, is defective (or just weak) in design or manufacturing?

or

B) How to determine whether a specific _individual_ rifle has a hidden flaw?

The answer to A is clearly destructive testing on many individual examples, such as what the Army did (see Hatcher’s Notebook). That answer is obviously not helpful if you’re asking B.

 

[Dave DeLaurant]

B) How to determine whether a specific _individual_ rifle has a hidden flaw?

Bingo! Again, I made the mistake of writing 'strength' in the title when what I meant was 'soundness'.

 

[mshootnit]

I think many rifles are still proofed, I get a lot of dirty NIB barrels. They are at least test fired.

 

[lysanderxiii]

Bingo! Again, I made the mistake of writing 'strength' in the title when what I meant was 'soundness'.

NDI

Either FPI or MPI.

Inspection under 10X magnification will sometimes reveal flaws.

(You can go into gimbal-lock if you start worrying about subsurface flaws.)

 

[Slamfire]

I have examined books of Non destructive inspection techniques and come to the conclusion, I don't know. I don't know a non destructive test to determine quality of metal, heat treatment, and fatigue life remaining in carbon steel structures. The tests I have found require metal to be sectioned, micro-structure examined, and specimens to be tested on Charpy impact machines. These are destructive techniques.

The non destructive techniques that use the electromagnetic spectrum require a perfect specimen as a base line, but I don't know the location of that shelf full of verified perfect vintage actions.

With historical military service rifles, it is my opinion all you can do is examine structures for cracks or metal displacement. If the lugs or receiver seats are setting back, that is a good indication of materials that have been stressed beyond yield. If cracks develop, depending on where those cracks are, the structure is dangerous.

However, I am just a dabbler in NDI technology, and maybe a real NDI expert can provide a good answer.

In so far as systemic design issues, go read Vol 1 and Vol 2 The Bolt Action by Stuart Otteson.

While I find the Ackley blow up tests fun, what they show is the amateurism and sensationalism of P.O Ackley. His test are slightly more informative than strapping explosives to stuffed animals and blowing them apart. To Ackely, and Ackleyites, the single most important characteristic of a rifle action is the amount of powder it takes to blow it up. They ignore vital functions such as feed and extraction, parts durability, ease of repair, cost of manufacture, weight, gas venting, etc, etc. Nope, to P.O Ackley, how good an action is, is determined solely by the amount of explosives it takes to turn the thing into shrapnel.

All military service rifles were issued with military service rifle ammunition which was made, inspected, to pressure specs to ensure safe and reliable function. Ordnance Departments did not encourage, nor promote, wildcatting by enlisted men. Soldiers were expected to use their service arms as is, with the ammunition issued to them. Therefore, all the over pressure conditions that Ackley created with his wild cats, was not a concern in the design and build of the things.

Anything created by man can be unmade by idiots.

 

[redneck2]

Anything created by man can be unmade by idiots

That’s good

 

[lysanderxiii]

I have examined books of Non destructive inspection techniques and come to the conclusion, I don't know. I don't know a non destructive test to determine quality of metal, heat treatment, and fatigue life remaining in carbon steel structures. The tests I have found require metal to be sectioned, micro-structure examined, and specimens to be tested on Charpy impact machines. These are destructive techniques.

The non destructive techniques that use the electromagnetic spectrum require a perfect specimen as a base line, but I don't know the location of that shelf full of verified perfect vintage actions.

With historical military service rifles, it is my opinion all you can do is examine structures for cracks or metal displacement. If the lugs or receiver seats are setting back, that is a good indication of materials that have been stressed beyond yield. If cracks develop, depending on where those cracks are, the structure is dangerous.

However, I am just a dabbler in NDI technology, and maybe a real NDI expert can provide a good answer.

In so far as systemic design issues, go read Vol 1 and Vol 2 The Bolt Action by Stuart Otteson.

While I find the Ackley blow up tests fun, what they show is the amateurism and sensationalism of P.O Ackley. His test are slightly more informative than strapping explosives to stuffed animals and blowing them apart. To Ackely, and Ackleyites, the single most important characteristic of a rifle action is the amount of powder it takes to blow it up. They ignore vital functions such as feed and extraction, parts durability, ease of repair, cost of manufacture, weight, gas venting, etc, etc. Nope, to P.O Ackley, how good an action is, is determined solely by the amount of explosives it takes to turn the thing into shrapnel.

All military service rifles were issued with military service rifle ammunition which was made, inspected, to pressure specs to ensure safe and reliable function. Ordnance Departments did not encourage, nor promote, wildcatting by enlisted men. Soldiers were expected to use their service arms as is, with the ammunition issued to them. Therefore, all the over pressure conditions that Ackley created with his wild cats, was not a concern in the design and build of the things.

Anything created by man can be unmade by idiots.

You can through magnetic field strength measurements get a rough idea of case depth, and the approximate authensite, martinite, pearlite, etc, percentages. But, it is not something that is easily done.