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.
Now, how are you testing the spring weight?
I've been playing around with the trigger weight set, but I can't get a set up designed that I'm sure is testing the spring, and I'm not sure what point I should test it at.
Fully compressed? Uncompressed?
What matters?
Interesting stuff Tuner... but... this 0.2... that is 2/10 = one fifth, yeah?!
So... 900 x .2 = 180!! So should it not be 0.02?!
Seems like a good approach for a rule of thumb.
By Jove P95... You're RIGHT! It is .02 Gettin' old is a pisser ain't it? I worked that thing out about 15 years ago...
Good eye! Keep me on my toes.
Jammer asked:
Now, how are you testing the spring weight?
With a spring tester, available from Brownells. Not a clue on how much... Mine is 20 years old.
Fully compressed? Uncompressed?
Compressed. It requires measuring slide travel, plugging in the length of the spring with all coils touching, or stacked solid. (Number of coils X wire diameter.) Then subtract to get the length of the spring as installed in the gun with the slide fully rearward. This will give you the loading for that spring in that pistol at full slide travel when you compress it to length in the tester.
Ok I've seen my gunsmith buddy do some "figgering" for spring weights, and not just for the 1911 with 45ACP (9x23, .38 Super...) so this must be what he was doing. Umm, see he does metallic, I do shotshell err, "figgering". [I know I know we each make our mess in respective corner of his shop]
Since none of mine have FLGR... then the theory of recoil spring for standard 230 gr ball launches GI Plug to lathe, and for 200 gr to band saw,and for 185 gr to fridge... is not a hard fast rule - huh ? NO matter seems to work fine for the loads I use and "figgering" - this way - seems to work... in his shop...
Oh if a shock buff is used for the range stuff... that has to be "figgered" in too it seems.
FWIW a brass case used for the plug will dent the fridge deeper than the lighter aluminum GI plug... in case you need to win a trival deal for free coffee... it is true, I have tested more than once so to add to to the scienetific community, research you know.
sm figgers that:
Oh if a shock buff is used for the range stuff...that has to be "figgered"
in too it seems
And he figgers right. The shock buff increases the preload on the spring, which would increase the compressed loading, which brings up another point of interest that slipped my mind.
Take a 32 coil spring (GM length) with a 16 pound rating. Assuming that it truly is 16 pounds at full working compression as installed, if you cut that spring down to 24 coils so that it will work in a Commander, the preload is greater than in the 5-inch gun, and the compressed loading will actually be a bit higher than 16 pounds. This opens up all sorts of avenues for spring tuning. I never order springs made specifically for a Commander any more. I order full length springs and cut to fit and function.
Note that the 24 coil specification is a MAXIMUM, and most Commanders operate best with 22-23.5 coils. Whenever trying this, be sure to check for coil bind in every pistol that you cut a spring for. For that matter, check for coil bind ANY time you change a recoil spring. If the spring goes solid before the slide reaches the impact surface in the frame, the least it will do is ruin the barrel bushing. I've seen coil bind destroy a Colt slide within 20 rounds. Not pretty. Never assume. Check it.
Now, use that formula to figger a spring rate for a 124-grain bullet at 1150fps and see how close ya get to factory specs for a 5-inch 1911 in 9mm. (10-11 pounds) and a .38 Super for a 130-grain bullet at 1250... (Industry standard for the thutty-eight Soup)
Then, just for kicks... look in the Colt section of a Brownells catalog for the Government Model recoil spring part number. You may be surprised that the same part number covers .45 ACP and .38 Super... about 14 pounds.
Note also that the two springs that used to come with the Gold Cup... one for hardball and the other for "softball" or reduced target loads are identical in every way except one. The difference? 3 coils.
Fascinatin' stuff... wot think?
Touch on the deal if one uses the buff at range and removes for carry in the same gun, with same spring, what one needs to be made aware of.
I was being a bit of 'character' but this can get serious quick, especially in a defensive situation. My thinking and concerns are simple. The 1911 style platform was designed to do a job and do it well. Deviate anything from the original, and many things built into that design WILL change. Reliability is paramount, in any defensive firearm, I get chided because being a "fuddy- duddy", I don't deviate... very little if anything on my defensive firearms... and not just the 1911 platform either.
Gun fit to shooter, reliable ammo in that gun everytime, that shoots POA/POI with the largest caliber that affords quick accurate hits for the said shooter.
I used to use the 18lb springs in my 1911s but now favor going to 14lbs. I even have one gun I'm experimenting with a 10# spring, using 200gr SWC over 4.0gr of Bullseye, and I use a CP buffer in that gun.
Since I now handload, also Tuners fault, I tend to shoot milder loads. Right now I'm stuck on 230gr LRN over 5.0gr of RedDot.
You hit on the one thing that I've tried to get across to people for years, with limited success. To wit:
Whenever anything is changed, it affects everthing else... and whenever a successful design is modified, three other things usually have to be changed to compensate for the improvement. That being said...
A shock buffer takes up space in the spring tunnel, effectively increasing the spring rate across the board. Some pistols are more sensitive to that increase than others, and in those, a buffer can bring on functional issues. The 5-inch guns are, as a whole, less prone to this than ones with shorter slides because they have a goodly amount of distance behind the magazine. Look at the distance from the breechface to the center of the disconnector on a Government Model and compare it to a Commander to see it. Another point is that a shock buffer dampens the impact between the slide and frame, and reduces any "bounce" in the steel. This can work for or against function, depending on the gun. Again, in 5-inch guns, this doesn't have the same effect as in shorter pistols.
Two identical pistols can exhibit completely characteristics with a buffer. I have two older M-1991 A1 Colts. One can't tell the difference, and runs fine with a buffer in place while the other one goes into spastic fits. Both are equipped with a 16-pound Wolff spring, and swapping the springs doesn't make a hill of difference. The "bad" pistol will even lock the slide with ammo in the magazine about every third round... or sometimes more often. Take the buff out, and it goes back to dead nuts reliable. Both these pistols will run with springs ranging from 14 to 18 pounds with nary a hitch as long as the buffer stays out of the one. Go figger.
Using a buffer with the same spring as for carry MIGHT cause the spring to take a little more set than it would without it, depending on how heavy the use and how long it's in the gun. I normally use a buffer in guns that are range-use only, and let the springs completely relax between sessions.
A recoil spring is a multi-tasked machine, and many people don't understand the difference between Load and Rate. The load rating of the spring tells only half the story. It specifies the spring's resistance at full working compression. The RATE is a different set of numbers. Rate determines how quickly the spring unloads its stored energy. It's possible to take two lengths of the same tempered wire and wind one with more space between coils than the other, and completely change the operating characteristics of the spring. Not only will the maximum loading be higher, but the spring will be "faster" too. Therefore, if a spring takes a little more set due to a solid spacer in the tunnel, the spring will be made a bit weaker than one with normal set. Whether a .120 inch thick shock buffer will have enough effect to make a practical difference is unknown... but probably not. On the other hand, EVERYthing means SOMEthing, and nothing can be discounted. In this instance, the only likely difference will be that the spring's life will be a little shorter, but in a pistol that is finicky about what spring load and rate that it likes, it could make a difference.
My advice on a dual-use pistol is to have one recoil system for the range and one for carry... both tuned/tested in the gun, especially if a buffer is used on the range. Letting a spring relax at its free length is also a good thing to do to extend the life of the spring. Spring tempered steel has a strong memory, and the spring will "unset" a little if allowed to relax, preserving its strength. It won't return to its pre-set length, but it will regain some of it.
Think of a coil spring as a torsion bar that's been wrapped around a mandrel into a helical shape. Its energy and resistance to twisting is related to its length, preload, diameter, and distance of applied force... and in the case of a coiled torsion bar... the distance between coils. Also consider that the spring is nothing more than a straight length of steel formed into a helix. If a length of steel is cut shorter, it gets stiffer. If the distance between coils gets wider, the length between any two points is shorter. Study that for a minute and it'll come to you... There's something in there that Hooke's Law will explain better than I can, but it's related to the shear modulus of the spring.
Coming next: How to slow the slide down in recoil without speeding it up in the return to battery... Some already know. Shhhhh.
I give up, how does one slow the slide down in recoil without speeding it up in the return to battery?
Here is a calculation I did 4 years ago, but it is still ok:
CAUTION: The following post includes loading data beyond currently published maximums for this cartridge. USE AT YOUR OWN RISK. Neither the writer, The High Road, nor the staff of THR assume any liability for any damage or injury resulting from use of this information.
Example:
Patriot 45acp {now Cobra} LINK 404
15 pound to start and 42 pound spring at the rear [home made spring assembly], is just right for 10.3 gr of AA#5. That is, it is just enough powder to keep the Patriot from jamming with that spring.
The bullet leaves the gun at 1100 fps.
The bullet weighs 185gr = 185/7000 = .026 Lb.
The slide weighs .5 Lb.
The barrel weighs .1 Lb.
The spring is 15 Lb to start.
The spring is 42 lb at back.
The momentum of the bullet equals the momentum of the slide and barrel.
[1100][.026]=V[.5+.1}
V=47.7 feet per sec
Velocity of slide and barrel = velocity of slide
Energy of slide = .5mVV= one half mass velocity squared
Es=.5[mass of .5 pounds][47.7][47.7]
Mass = [wieght]/gravity= .5/32.2=.0155
Es=.5[.0155][47.7][47.7]=17.64 foot pounds of energy
The energy required to pull back the slide = [force][ distance]
Force = average force = [15+42]/2 = 28.5 pounds force
distance = 1.656"=1.656/12=.138 feet of slide stroke
Eslide = [28.5][.138]=3.93 foot pounds
BUT WAIT A MINUTE! 17.64 DOES NOT EQUAL 3.93!
Not all of the bullet momentum went into the slide and barrel.
Some of it accelerated the hand.
Only 3.933/17.64= 22% went into the slide and barrel.
What does this mean to someone who wants to calculate the spring needed for a semi auto pistol?
Heavy firm hands need stiffer springs than soft light hands and there is no good way to measure how light and soft one's hand is.
So, you cannot accurately calculate the spring you need.
Clark said:
and there is no good way to measure how light and soft one's hand is. So,
you cannot accurately calculate the spring you need.
That's why I used the 16-pound spring as the constant instead of going with the standard advice of using the heaviest spring that will allow the slide to lock on empty. Most of them will do that, even when badly oversprung. Using these calculations will let the gun function through full magazines cradled on the hand with just the thumb and index finger gripping it lightly and the wrist bent on two planes.
Every gun will differ to some extent as to which spring rate and load that it will run its best with... but these figures will get you real close, and in most cases will work just fine for the average shooter, regardless of the grip.