What's a 10 pound spring?

[garrybuck]

I've been following the various spring discussions with some interest. I'm beginning to wonder if there's a difference between what an engineer means and what a gunsmith means when they say "10 pound spring."

To an engineer, it means that every inch of compression is going to cost you 10 pounds, i.e. if you mash a 10 pound spring 3 inches, that will take 30 pounds. A 20 pound spring mashed 3 inches will take 60 pounds, etc.

I've got a get a sneaking suspicion that it's not that way for gunsmiths. I'm beginning to suspect that "10 pound spring" means, it takes 10 pounds to rack the slide.

The reason I'm beginning to think that is, it takes about 21 pounds to rack the slide on my Mak when it has a 21 pound Wolff spring, and it takes about 19 pounds with the 19 pound spring.

Is this indeed the standard convention in the gunsmith trade? Is it just a marketing thing to make things simple?

Not that there's anything wrong with that, but in my world, a spring that takes 21 pounds to mash 3.5 inches is a 6 pound spring.

Now, I'm not picking on gunsmiths in general or Wolff in particular. I have enormous respect and trust for both. All I'm saying is, if there's a fundamental difference in terminology among engineers, gunsmiths, parts suppliers etc., we need to be very careful, especially when it comes to swapping springs between different guns.

[abwehr]

garrybuck,

You make a valid point. I am an engineer and when springs are calculated I use the "inch compresssion rating"! I have never checked the weight of pulling a slide with a particular "weight" spring from someone like Wolff.

Normally, I don't change springs from the original since a particular spring should have been "engineered" for that particular pistol and a particular round. Once you change to different rounds like the ++P rounds, yes, springs do need to be changed to keep from "beating" the pistol. The way Wolff and others rate the spring tension may certainly be an easy way for the average shooter to determine which spring he needs.

Great postings; I hope someone has an answer!!

[mongo]

Wolff KNOWS springs..

Do not question them..

HAHAHA

[raypol]

The weight necessary to compress the spring to about 85% full compressed is how recoil springs have been measured and reported on the gun forums. There is a good article on building a spring weight measuring tool on one of the forums. I printed it and forgot where I saw it. I'll try to find it and post it.

[garrybuck]

Very interesting. Now I think there are three systems: spring rate, what it takes to mash it 85%, and what it takes to rack the slide. :-/

The difference in approach leads to the following situation:

Consider a spring, 10 inches long, with a spring rate of 10 pounds per inch. To an engineer, it's a 10 pound spring. Assuming an ideal spring (no mass, no thickness, no aerodynamic drag, no cholesterol, etc. etc...) it will take 85 pounds to mash it down to 85%. Hence, the forum will say it's an 85 pound spring.

Now, cut the spring in half, so you have a 5 inch long spring. To an engineer, it's STILL a 10 pound spring. However, the forum would say it's now a 42.5 pound spring. But if you go by what it takes to rack the slide, THAT would depend on what gun you put it in. It could be anything from zero to impossible.

Does any of this nerdy hairsplitting really mean anything? No, not as long as you're using wonderful Wolff springs in the EXACT gun they're intended for. But the moment you start taking springs from one gun, clipping coils off, and putting them in a different type of gun, the meaning of the numbers gets really hazy.

I'm not saying not to do it, I'm just saying be careful, measure everything yourself, be paranoid.

Sorry for being such a nerd. You know us engineers, always turning things into a bloody life or death issue. But, ya know, if you use a 10 pound spring when what you really need is a "10 pound spring," it really could turn into a bloody life or death issue.

Ok, I'll shut up now.... :-X

[abwehr]

garrybuck,

You and I think alike on the Spring Weight discussion. A spring calculation requires more factors to be considered such as max length the spring can be when collapsed, the mass of the slide with components, travel length, maximum allowable spring compressed length, force exerted on the slide from the resulting cartridge detonation, etc. This is not an easy calculation and I will wait on Wolff to provide the details and then buy. Am I a lazy engineer???

[novgarod]

Have you ever wondered what spring calculation the Polish army officers used to design a pistol with a double action trigger pull of 120 newtons? Now those folks really needed some help! You gotta laugh!

[garrybuck]

Abwehr: Lazy, no. Smart, you betcha! I'm a civil engineer, my idea of fixing something is to bury it in concrete. In my world, when things move, it's a bad thing. Moving parts make me nervous, so I'll leave it to the Wolff pack to figure this one out for me. No spring swapping for me.

Novgarod: I've got a few Polish relatives. I'll tell ya, they got some big bubbas over there. To a strapping Polish farmboy, this is probably a hair-trigger!