1911Tuner
Moderator Emeritus
There's been a rash of discussions on recoil springs lately. The prevailing question seems to be: "What is the best/correct spring rate for ammunition X in 1911-pattern gun Y" and the concerns are with frame damage. It rarely comes up in a discussion on any other platform.
The generally accepted line of thought is that The Commanders and Officer's Models require heavier springs because the faster slides hit the frame harder...and that without the added deceleration afforded by the heavier springs, the frames will be quickly beaten into junk.
*cough*
Somewhere along the line, we were told these things, and because it made sense...we readily accepted it. The problem is that it's not based in fact. It's based either in opinion...or it's based on the "Dog in the Fight" theory from people who make money selling springs and such amenities the familiar shock buffer.
If...and this is a big "IF" for many people who can't let go of the energy mindset...if we accept that momentum is the factor that does damage in any impact event, we can take the argument apart and discover the truth. The key lies in Newtonian physics. Good ol' Isaac to the rescue again.
In Newton's 3rd Law of action and reaction, we know that there must also be equal momentums on both sides of the system. Simply put, the slide's momentum can't be greater than the bullet's...but equal momentum only exists in the absence of outside force, or in the presence of equal outside force.
The Commander slide is faster with a given ammunition than the 5-inch gun's slide...but it hits the frame no harder...because the momentums must be the same. Lower mass requires greater speed to achieve equal momentum...all else assumed to be equal.
The slide's momentum can't be greater than the bullet's. Straight up can't happen. Let that simmer a while.
The shorter barrel of the Commander produces less bullet velocity, and because momentum is a function of Mass X Velocity...less bullet momentum. Less bullet momentum means less slide momentum...because the two are equal with equal springs and equal ammunition.
And another aspect is that, the lower the mass of the moving object, the faster its deceleration rate whenever it encounters a given outside (resistive) force. So, even with equal springs and ammunition...the Commander slide doesn't hit the frame quite as hard as the 5-inch slide.
I'm fairly certain that Colt's engineers are aware of these things...yet they use heavier springs in the short pistols. It seems that's backward thinking. If the momentum is lower, and the impact stresses are less...why not use a lighter spring? The slide needs a certain level of momentum to complete the trip backward. Installing a heavier spring would seem to compromise that...yet they do it.
Why?
Because the "Recoil" spring's function is in accelerating the slide forward...not decelerating it. The less massive slide requires extra speed to achieve the momentum needed for a reliable return to battery. After all...the resistive forces on the slide when it's moving forward are pretty much identical in both guns, and those resistive forces have to be overcome.
Before the energy question comes up, take a look at energy vs momentum as the destructive force.
Compare the 5.56/M193 cartridge to the original .45-70 "Cavalry" load.
55 grains at 3250 fps vs 405 grains at 1300 fps. There is little difference in the respective muzzle energies. Yet, the .45-70 slug will drive through a bull Elk lengthwise, while the .22-caliber pill probably won't get past the heavy chest muscles. Momentum.
Consider the loaded semi at 60 mph that nearly takes an abutment out from under a bridge while the Ferarri at 150 splatters like a bug on a windshield. Momentum.
The generally accepted line of thought is that The Commanders and Officer's Models require heavier springs because the faster slides hit the frame harder...and that without the added deceleration afforded by the heavier springs, the frames will be quickly beaten into junk.
*cough*
Somewhere along the line, we were told these things, and because it made sense...we readily accepted it. The problem is that it's not based in fact. It's based either in opinion...or it's based on the "Dog in the Fight" theory from people who make money selling springs and such amenities the familiar shock buffer.
If...and this is a big "IF" for many people who can't let go of the energy mindset...if we accept that momentum is the factor that does damage in any impact event, we can take the argument apart and discover the truth. The key lies in Newtonian physics. Good ol' Isaac to the rescue again.
In Newton's 3rd Law of action and reaction, we know that there must also be equal momentums on both sides of the system. Simply put, the slide's momentum can't be greater than the bullet's...but equal momentum only exists in the absence of outside force, or in the presence of equal outside force.
The Commander slide is faster with a given ammunition than the 5-inch gun's slide...but it hits the frame no harder...because the momentums must be the same. Lower mass requires greater speed to achieve equal momentum...all else assumed to be equal.
The slide's momentum can't be greater than the bullet's. Straight up can't happen. Let that simmer a while.
The shorter barrel of the Commander produces less bullet velocity, and because momentum is a function of Mass X Velocity...less bullet momentum. Less bullet momentum means less slide momentum...because the two are equal with equal springs and equal ammunition.
And another aspect is that, the lower the mass of the moving object, the faster its deceleration rate whenever it encounters a given outside (resistive) force. So, even with equal springs and ammunition...the Commander slide doesn't hit the frame quite as hard as the 5-inch slide.
I'm fairly certain that Colt's engineers are aware of these things...yet they use heavier springs in the short pistols. It seems that's backward thinking. If the momentum is lower, and the impact stresses are less...why not use a lighter spring? The slide needs a certain level of momentum to complete the trip backward. Installing a heavier spring would seem to compromise that...yet they do it.
Why?
Because the "Recoil" spring's function is in accelerating the slide forward...not decelerating it. The less massive slide requires extra speed to achieve the momentum needed for a reliable return to battery. After all...the resistive forces on the slide when it's moving forward are pretty much identical in both guns, and those resistive forces have to be overcome.
Before the energy question comes up, take a look at energy vs momentum as the destructive force.
Compare the 5.56/M193 cartridge to the original .45-70 "Cavalry" load.
55 grains at 3250 fps vs 405 grains at 1300 fps. There is little difference in the respective muzzle energies. Yet, the .45-70 slug will drive through a bull Elk lengthwise, while the .22-caliber pill probably won't get past the heavy chest muscles. Momentum.
Consider the loaded semi at 60 mph that nearly takes an abutment out from under a bridge while the Ferarri at 150 splatters like a bug on a windshield. Momentum.
