spring rate impact on velocity?

I swapped in a 16 lb and took out the factory 18.5 lb (confirmed the outgoing with Baer and the incomming was in a sealed Wolfe package. I even miked the two and the slight differences in #coils and wire dia. reinforces these weights). My standard load, all components being the same, and even shooting conditions nearly identical, dropped in velocity 75-100 ft/sec. I made the change because I was on the hairy edge of reliability with the old spring and did not want to bump up the charge. So yes, I am no better off; now at only about 650 ft/sec I still got the same 2-3 rounds out of a 30 shot practice match that did not completely cycle the slide. What's up? Thanks.

Velocity can not be effected by a 1911 recoil spring, when a 45 shell is in the barrel and hit by the firing pin the bullet has left the barrel before the slide ever begins to move. What will effect velocity is, the case, the powder, the primer, the crimp, the bullet, the bullet seating depth, bullet diameter,Even different lots of the same powder can give different results, and also you might consider your powder measure being off and probily some other factors i omitted. So if you have changed any of
these in your present load than your tested load then imo thats where
you lost FPS.

What was the ambient temperature when you chrono'd last time? Cooler temperatures can cost you about 100 ft/sec.

Thanks guys,

I suppose there might have been a max delta of about twenty degrees between the to sessions; I just don't recall when I first chrono'd that standard load. At least I knos my spring did not cause it.

I appreciate the guidance.

Ed

Yes i knew i forgot something, certain powders are very temperature sensitive, that's one reason bullseye powder is the predominate powder used it is not very sensitive to temp changes.

If you are on the edge as far as function goes put the 18.5 lb spring back in and change out the MAIN spring for a lighter one.
This will increase your slide speed and it will still have a stout spring to chamber the next round. You may have to tweak your trigger pull as this will become lighter when you install the lighter main spring. It's all about balance! As long as you have good ignition you are OK with the lighter spring.
I shoot a 38 special with 2.8 gr of BE in a long heavy slide with a 4-dot on the slide.

Dave C.