Springs! Specifically...recoil springs. The subject of much debate and conjecture...and one of the least-understood facets of the gun.
I've never really understood how they came to be known as "recoil"
springs in handguns...and "action" springs in rifles and shotguns...but that's academic at this point...so we'll just call'em recoil springs....but technically speaking, they're action springs. The recoil function is simply
a means to transfer kinetic energy to the spring, so that the other half of the cycle...feeding and returning to battery... can be completed.
It's an auto-LOADER...not an auto extractor/ejector. The primary function
of the spring is to reload the chamber without manual assistance. All else is secondary...
The spring can also be a means to absorb recoil and spread its effects out over a longer time frame...as with the Howitzer...but weapons like these are single-shot, and the heavy recoil is controlled by these springs in order to negate having to reposition the weapon for follow-up shots.
In systems such as these...the recoil spring is truly a recoil spring.
A few things to keep in mind:
Springs work both ways. They compress to store energy, and they
un-compress to release energy.
They have to balance their function so that they'll be able to perform both tasks within the design parameters of the machine that they're assigned to. The engineers who settled on a particular spring rate had very good reasons for their choice. Changing that balance by going very far out of the window very often has adverse effects on the function of the machine that may not always be immediately apparent.
The speed of the complete cycle of an autopistol doesn't change to any real degree by changing the rate of the recoil spring. The total time difference will be within small fractions of a second, if at all. The change in speed is in one direction, and is compensated for in the reverse direction. The heavier spring slows the slide in recoil, but speeds it up on the return to battery, and vice versa.
Energy can't be destroyed. It can only be redirected.
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The recoil spring in a locked-breech weapon doesn't prevent impact damage to the frame and slide unless the spring is so heavy that it doesn't allow full travel. It only softens the blow...a little. While it's true that a heavier spring softens the blow a little more, it does so at the expense of the parts that impact on the return to battery. In the 1911, this would be the lower barrel lug...specifically the feet...and the slidestop crosspin. So...you 18 and 20 pound spring users are offering the frame and slide abutments a bit more protection while redirecting the impact forces into another area of the gun. Think about it. The frame and slide impact surfaces are engineered to absorb shock stresses. The lower lug feet aren't.
The recoil spring in a locked-breech design doesn't do anything at all to contain chamber pressures, and it has very little to do with the timing of the unlocking phase.
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In the recoil function study, we've established that the beginning of the unlocking event comes after the bullet is gone, and chamber pressures have fallen to nearly nothing. It has to. If unlocking began while the bullet was still in the barrel, a case rupture would almost surely be certain with every round fired. A couple years ago, master pistolsmith and mad scientist Ned Christiansen fired a 1911 pistol repeatedly without a recoil spring...without ill effect, and with very little change in point of impact on target as fired from a machine rest...offering proof that the unlock timing
was only affected by the spring's preload and compression during the
first 1/10th inch of slide travel. The preload of a 16-pound spring in a 5-inch gun averages about 3 pounds. An extra 1/10th inch of compression would increase that preload very little. So, the difference in the effect on unlock timing between a 16 pound spring and a 20-pound spring would be about the same as the pressure that you put on the space bar on your keyboard as you respond to this.
A heavier-than-standard recoil spring DOES have an effect on the
timing of the return to battery. While the dynamics of the event will be mechanically the same...it all happens at a faster rate. Think of the spark advance in an automobile's ignition system. As engine rpms increase, the spark must occur at an earlier point in the piston's position before TDC in order to keep up, or the engine suffers a loss of overall performance.
In the case of the autopistol, the problem is with the magazine's ability to keep up with the slide. The magazine spring has a daunting task. It not only has to lift the rounds upward in the magazine while being jerked around during the pistol's recoil cycle...it has to get the next round into position in time to meet the breechface. The faster the slide moves as it returns to battery, the less time the magazine has to put the next round into position. If the magazine spring isn't up to the task, we have classic bolt-over-base and rideover feed malfunctions. In these...the slide is outrunning the magazine.
The second part of the problem is that...if a jam does occur...the heavily sprung slide jams it harder. Think of a wedge-type doorstop. If you push it in place with thumb pressure, you can pull it out easily. If you kick it in place hard with your foot...it's tougher to remove. Often...when we have
failures to return to battery with the round part-way into the chamber...we get the advice to "Try a stronger spring." While a stronger spring may well
force the round to chamber in spite of the problem...this is usually counterproductive. Better to address the real problem than put a band-aid on it. If the gun is correctly set up, it should feed and go into battery easily with an 8 or 10 pound spring.
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