An excellent thread from another forum by someone who appears to be quite knowledgeable. I'd be happy to introduce the poster, but I don't know him, I only found the site today. Since we've been tossing around spring rates recently, I thought this article would be appropriate
http://www.thehighroad.org/showthread.php?s=&threadid=57241"A question that often comes up is: "How heavy should my recoil spring be for X bullet weight at Y velocity?
The usual advice is to step up the spring loading as pressure and velocity
increase. For example, the common advice when using a 185-grain +P+
scorcher is to move up to a higher level on the recoil spring. The catch is
that cartridge pressure has little to do with it.
Ned Christiansen conducted a test in which he fired a 1911 pistol without a recoil spring in the gun. There was little, if any, effect on the timing of the barrel unlocking from the slide...so the loading of the recoil spring doesn't play much of a role in containing pressure. Therefore, we can accept that the difference between a 16 and a 20 pound rating is pretty much insignifigant when the slide is in battery, and the effect that either have in keeping the barrel and slide locked together is virtually nil.
Now, most of us know that the standard recoil spring for the 5-inch
pistols is 16 pounds, and 18 for the Commanders. Shorter pistols are
in a class to themselves, and come with their own set of nuances,
so I'll keep this confined to the two variations mentioned above.
The problem with increasing the spring rate beyond certain limits is that it
can bring on certain issues related to the slide timing. The spring works both ways. Slow backward means fast forward, and vice-versa. For the record, I have never found a new Colt Commander or Combat Commander with a factory spring that tested at 18 pounds, and the bigest majority of 5-inch Colt springs don't test at 16...and I've made a nuisance of myself at local shops by going around testing them. The Commander springs generally fall between 16 and 17, while the GM class rarely go over 15 pounds at full compression....just shy of coil bind. Another thing that I've noticed is that very often, two springs in identical pistols will vary a little on the coil count...one-half to one full coil. Why? Are they being tuned to the gun on an individual basis? Colt isn't talking, so I have to assume so, and the reason is...again assumed...to make the pistol less dependent on the magazine spring tension. The slower the slide moves forward, the more time the magazine has to get the round in position.
I've often tuned springs to guns by clipping coils. Rule of thumb is if I can't
get what I want with a maximum of two coils removed, time to drop to the
next level and start over. It's worked well for me. Again, my main concern is reliability, and not 100,000 rounds downrange.
This is all easy enough when using hardball ammo, or the equivalent in
terms of velocity and bullet weight...but where do we start when trying
something different? Where do we start? One approach is to buy several
springs in various loadings and try them all. Not very cost effective, and
we wind up with a few unused springs lying around. What to do?
By working some numbers in reverse, I've come up with a formula that
works...Not always with all pistol/ammo combinations, but it will get you
very close 99% of the time. It works thus:
Multiply the velocity by .02 (Point Zero 2) and that is your spring rate for a
230 grain bullet at hardball-spec velocity in a 5-inch gun. If we take
230 at 830fps +/- 25 fps(Ordnance hardball spec) we find that the
spring rate will work out at somewhere between 16 and 17 pounds.
Browning split the difference at 16.5 for his pistol. Coincidence?
Now, a 200 grain bullet at 900 fps. 900X.02 gives us an 18-pound spring,
but the bullet mass is reduced. To account for that reduction, figure the
percentage difference between the 230 and the 200 grain bullets. It
works out to about 11% difference. 11% of 18 is 1.88...round up to
1.9 and subtract. We're back to the 16 pound spring, or very close.
Using a 230 at 900 fps? An 18-pound spring should do nicely. A 200 at
1,000? 1,000X.2=20-1.9=18.1...An 18-pound spring will get you very close to optimum without going too high unnecessarily.
Commander? Again, we're dealing with mass and velocity. Plug in the
percentage difference in slide weight...In this case, the Commander slide is
about 10% lighter than the GM slide, on average. This time, ADD the difference. A 230-grain bullet at 830 fps takes a 16-pound spring in a
5-inch gun plus 10%, works out to be...well, whaddaya know...17.6
pounds, or very close to the accepted standard for Commanders.
Dropping down to a 200 grain bullet in a Commander? Add the difference in the slide weight, then subtract the difference in bullet weight, both from
the 16-pound constant.
Some few like to use a heavier bullet...say 250 grains at 750 fps. Now
we ADD the percentage difference in the bullets. Here, VelocityX.2 gives
us a 15-pound spring. Adding the percentage difference of the bullets
results in an adjustment of about 8%, and we have a 16.2-pound spring.
A variable 16.5 pound Wolff should do nicely here.
One thing to keep in mind is that springs, like any mass-produced item,
have tolerances. They vary. Just because the package says 16 pounds doesn't mean that it will TEST at a true 16 pounds. It may test at 16.5.
Clipping a half-coil off a 32 coil spring will reduce it roughly one-half-pound.
These figures and calculations won't be exact in any given pistol because
every pistol has its own characteristics. Of two identical guns, one will
do fine with a heavy spring, and the other won't. These formulas will give you a good starting point, and nothing more. Most of the time, it works.
Once in a while, the pistol will defy all logic, and go in the opposite direction. All this assumes that the magazine springs are up to the task of
reliable feeding, and that the barrel and throat are good.
Luck to ya!
Tuner"
