Light recoil springs bind up?

[ropati]

I've got a 75B SAO that has the factory length (short) guide rod.  I know that it is normal for the rod/spring to not be perfectly straight in normal operation.

I'm currently shooting very mild 9mm practice loads and want to try a lighter recoil spring (11lb)  But, when I do, the spring really bows a lot and it seems like it wants to bind as the slide runs.  Anybody have any experience/comments on this?

Thx

[painter]

Lighter springs are in fact longer.

I have a 13 lb spring in my 85C, and while it will bow out the slide never binds.

Have you fired your pistol with the 11 yet?

[ropati]

I haven't tried the 11lb spring yet. It just seems like it wants to catch when I'm just racking the slide.

[Radom]

They will all take a set and shorten a bit, regardless of weight. 

I actually use my 75B SA to set the springs for my other 75/85 pistols, as it always seemed to do a little better with a new spring.  There's no real objective reason for it, but at least it makes me feel better...

[1SOW]

I once ordered an 11# spring from CZC for my 75B 9mm.  The spring did exactly as yours is doing.  It would actually prevent the slide from being retracted unless it was put in as absolutely straight as possible by rotating the guide rod and spring until very close to being straight.
I asked CZC about this problem and the response was "cut off two or three coils"
 

As Radom said,  if you install it as straight as possible and lock the slide back for a while,  it'll take a set in that condition that will function.
Cutting off two coils also worked. 

[ropati]

Any thoughts on what cutting off two coils does to the poundage of the spring?

[1SOW]

Your question was identical to mine when this happened to me.  The answer is "lighter" mostly.    My posts are here back in the last century section somewhere.

If it throws the cases 4-8 feet it's good-to-go whatever weight it actually has.  If it throws them too far, it's NOT.

I'd try giving the spring a set first.

[Radom]

Any thoughts on what cutting off two coils does to the poundage of the spring?

My understanding is that if you remove 20% of a spring's length (just as an example), the resulting spring is NOT 80% as strong as before.  It's somewhat weaker.  IIRC, it has to do with altering the temper of the steel, and the nature of coil springs (i.e. "pure physics").  The resulting spring also wears faster than one that was never cut. 

I've seen major problems occur when this was taken to an extreme, but I am also aware of people who have done it with no problems.  I've never done it, but I once bought a used Ruger Security Six that had some problems for this reason.  Replacing the mainspring cleared it up, but it caused me a lot of undue stress in the meantime.