Why must gun springs suck?

[OlongJohnson]

Consider the lowly econobox with a biggish four-cylinder motor. Suppose it's geared to do about 2500 rpm at about 60 miles per hour. With proper maintenance, that engine should easily last 15-20 years in service and cover 240,000 miles. If we take 60 mph as an average, that's ~300 million cycles of its valve springs, at a typical rate of ~21 cycles per second. Lots of time will be slower, lots will also be faster. Typical temperature will be in the realm of 250 F. At the end of that time, the valve springs will still be serviceable. If we pull the engine apart to restore valve seats and piston ring/cylinder wall surfaces, we'll replace the valve springs so the new ones can go another 300 million cycles. Furthermore, I can usually buy those springs for about what a typical gun spring costs, when the gun spring contains far less material and is generally manufactured to much more variable standards.

In contrast, we're told to change many gun springs at 3000-5000 cycles. H&K USPs are dramatic outliers with a recommendation of the main recoil spring at 25k cycles, if I remember correctly.

(This semi-rant was inspired by contemplating the Manurhin MR73, considered by many to be at least among the finest revolvers ever made, where the most credible reports of serious operating problems seem frequently to be tied to poorly performing springs.)

From a 100,000 times difference in service life, a reasonable person might conclude that the vast majority of gun springs are either poorly designed applications, or the parts are made from crummy materials using crummy processes.

Any spring engineers in the house?

[Doc_Glock]

Could it have something to do the mass of the material in the spring? Valve springs are pretty beefy.

Possibly also how highly stressed the springs are? Maybe guns would have to be significantly bigger and heavier to accommodate million cycle springs?

Your question is a good one.

[Jim Watson]

Valve springs are short pitch, short stroke springs.
Fiorearm recoil springs are long pitch, long stroke. I think they are stressed more per shot than the valve spring is per rev.

[MickAK]

They do and they don't. There are plenty of people with very high round count Glocks for example, that go 'You're supposed to change that? Huh.'.

Guns cost more than they should because people are willing to pay for them. If every part on your mentioned econobox was marked up like gun parts are it would lose the econo label and nobody would buy the piece of shit. Correspondingly lower quality materials are able to be used because people that are into guns like messing with them and putting better parts on. People that aren't see a gun that either works or doesn't and probably won't get to the round count mentioned to change the recoil spring.

As far as the difference between gun springs and other applications of springs like automobile engines, reciprocating mass and energy available has a lot to do with it. Look at the difference in energy between even a tiny econobox engine and a 9mm round. I've never changed a recoil spring on a Bofors 40mm but I imagine they last longer.

[LOKNLOD]

Everything is a tradeoff. This is especially true for mechanical components in mass production items.

99% of guns will never see round count to wear off the new gun smell, let alone any springs. Of the remaining 1%, half of them are going to tinker and swap springs around anyway. The remaining 0.5% don't really mind swapping a $5 spring every X # of rounds and would probably do it anyway even if you told them they didn't need to.

[whomever]

I suspect Mr. Watson is on the right course - valve and recoil springs involve different design tradeoffs.


If you really want an outrageous example, 16 inch battleship barrels probably cost a zillion dollars and have a service life of a couple of hundred rounds. A $100 Jennings will outdo that by a couple of orders of magnitude (if tthe crappy springs don't fail first :-) ). Maybe the Navy should contract with Glock to build the barrels :-).

[JAD]

Recoil springs are abusively over stressed to produce slide lengths that folks want. That’s ok, since a) it’s a replaceable part, b) fatigue has a non-immediate penalty, and c) most people don’t put $10,000 of consumables through a $500 unit and think it’s a bad deal when the unit wears out.

[mmc45414]

As has been mentioned, a valve spring is probably 0.020 diameter and probably has to move 0.400 or less.

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[Clusterfrack]

I got over 100k cycles on a CGW CZ trigger return spring, and the sear spring on one of my guns has way more than that.