View Single Post
Old 11-14-2005, 16:59   #47
racine
Senior Member
 
Join Date: Jun 1999
Location: Deep South
Posts: 609
Thanks for sharing your thoughts. My question now is then why do factory ParaOrdnance 45, factory HK USP 45, Glock 22 mag springs shorten when kept loaded for 6 months or more? Most of my CCW mags are usually the pick of the litter, fired a few times to test their reliability with factory ball and defense ammo, cleaned then relegated to CCW or home defense duty. But I've noticed that in the process of bi-annually cycling them into an IDPA/USPSA match I invariably end up with cycling problems, specifically stove pipes or FTF the last 1 or 2 rounds. Examining the mags yields springs a full inch shorter than new factory or wolff springs. You will notice that these are all double stack mags in question. On the other hand I never saw these with my single stack mags whatsoever?! I saved these deformed and shortened springs for a few years until I decided I really had no use for them save being a reminder. So now I read your post and references to the Am.HG mag and now I'm perplexed. I happen upon a posting from an engineer on the 1911 forums who comments;

"...My other post follows:

I am a Mechanical Engineer. I cringe every time Am Handgunner treads into the field of engineering. Journalists who don't know what they are talking about should consult someone who has actual technical training.

Creep does happen in ferritic materials.

Plastic deformation does happen in over compressed or over extended springs. The question is one of proper spring design and choice of the correct metallurgy. All of the generalizations in the Am Handgunner article have extremely common exceptions. All of those generalizations reflect "invincible ignorance" on the part of the writer.

Whenever I read this nonsense in Am Handgunner I think I should write a letter. Then I think why waste my time?

Ever wonder why your recoil spring gets shorter with use? It is because the spring design is such that whatever steel Wolff uses creeps or even yields under the cyclic compression loading. The metal MUST move for the spring to become shorter at rest. There's no other way it can happen. BTW that's ferritic material.

Ever wonder why this happens faster with a Wolff spring than it does with an IMSI spring? Because IMSI (or Nowlin) uses Cr-Si alloyed steel, which (as heat treated) has a higher yield strength than the Wolff metallurgy, so the Yield Strength of the material is much higher, and the creep process is much slower.

This is not a subject for simpletons looking for a one size fits all answer. In some mags the spring may be very lightly loaded, or overengineered. In others, the opposite may be the case. The ultimate answer is tied up in the interplay of spring loading and design criteria, combined with choice of metallurgy.

You would have to understand the design criteria for the mag (some are really hard on the spring because of how many rounds they're trying to jam in there with a really short follower). You will have to understand the metallurgy of the string. Was it heat treated right? How do you know? If strain hardened, did the spring maker draw the material right? How do you know? Do you even know that the material is certified at the claimed composition?

Notice how one poster said some springs have done fine, and others failed quickly? Probably a QC problem with spring metallurgy or heat treat. Inconsistent from batch to batch.

This is why aerospace and military manufacturers require "certifications" for metallurgy and heat treat. The answer changes completely based on little details.

That AH blurb was typical of the type of uninformed drivel that they've been printing lately. Ever since they went to the format that has several blurbs on a page, their reporting has gotten less and less in-depth, and more and more generalized. And in technical subjects, generalizations are for fools. It is a technical subject BECAUSE THE LITTLE THINGS MAKE A DIFFERENCE. But these guys are too ignorant to even know what the little things are. That stupid writer may get someone killed.

In the meantime I'll be sure there are fresh springs in my carry mags.

BTW the ultimate strength of metal in a spring is irrelevant. Ultimate strength is the loading where the metal comes apart. In a spring design you don't want to go over the yield strength (another concept that Am Handgunner got garbled up). The definition of yield strength is a bit complicated, but suffice it to say that it is the point where the metal begins to plastically deform. "Plastically deform" is engineer-talk for "bend"

For those interested in actual knowledge on the subject, find a copy of "Mechanical Engineering Design" by Shigley and Mitchell. In my 4th ed (1983), Chapter 10 is devoted to spring design. Chapter 4 includes a section on Creep, and section 4-5 details creep effects of time and temperature on ferritic materials.

Here's an idea. How about we take all of our questionable springs and send them to that writer so he can install them in his carry gun's mags? Maybe we should make the offer!.."


Though I profess NOT to be an engineer, I do come from a scientific background and I am more inclined to depend on quantitative data and experience together rather than unsubstantiated claims, assumptions and experience alone.
Racine
racine is offline   Reply With Quote