This was sent to me by a friend down in Texas. Take it for what its worth.
Now is the point where those of you who really understand 1911-type pistols may want to go elsewhere, as what I write will be old hat to you.
As you all know, the 1911 was designed around a load running a 230 gr. bullet at about 850 fps., with a 5" barrel and slide to match. Originally, it had a 23 lb. mainspring and a 16lb. recoil spring, and the result was that it was extremely forgiving. Once we started trying to fool Mother Nature and Father Browning, things got interesting. First, there were wimpy target loads. Lightening the recoil spring and mainspring were about all it took to keep reliability. Then, there were .38 Supers, running a 130 gr. bullet at 1200 fps. or so, and again, not much was needed. Then, along came hot .45 loads, shorter, lighter guns, starting with Commanders with 4 1/4" barrels and matching slides with lightening cuts, and later, IPSC, and then, the 3 1/2", 3 1/4" and 3" guns, and 10mms, .45 Supers, .45 WinMags, .460 Rowlands, and lions and tigers and bears, Oh My! "Old Reliable" suddenly started having reliability issues.
It's all about the basic physics of inertia, momentum, levers and springs, and their interaction with each other. Lest anyone be overly concerned, there will be no formulae here, nor any quiz at the end. While I took 12 hours of university physics, it was only because my major required it, and I despised almost every minute, mostly because most physics professors just ain't right somehow. So, we'll stay qualitative and basically Newtonian. Much of what I've learned about the subject has come from trial and error, with lots of the "error" part, and other important information came from Dane Burns and other 1911 gurus.
For function to be reliable in a 1911-type, dwell time is critical. Dwell time is the time period between the primer igniting the powder and the slide slamming closed on the next live round. If the dwell time is a little slow, it is usually not a big deal, unless it is accompanied by short-cycling. With long dwell times, really good speed shooters start to complain, because they feel like they are waiting on the gun to finish, but function of the gun rarely suffers. I clearly and fondly recall when I was that good. Sigh... It is when dwell times get too short that problems start happening, and shorter, lighter slides and lighter springs shorten dwell times.
Heavier slides have more inertia, so it takes more recoil force to get the slide moving rearward. They also have more momentum when moving forward, helping chamber the next round, once the recoil spring gets the slide moving. The hammer resting (briefly) on the firing pin stop delays unlocking, so the heavier the mainspring, the less force reaches the slide when unlocking starts. It is the mainspring, far more than the recoil spring, that affects dwell time, especially on the recoil stroke. Heavier mainspring=slower unlocking=longer dwell time.
As regards unlocking, another major factor involves levers. In 1911A1 and later guns, nearly all of them have a smooth, rounded bevel on the bottom of the firing pin stop, where it contacts the hammer during recoil. I believe (correct me if I'm wrong--been too long since I actually held an original 1911) that the original 1911 design had a square bottom on the firing pin stop. This seemingly small difference is significant, because the square bottom fp stop significantly shortens the length of the lever portion of the hammer, where the hammer pin is the fulcrum. Shorter lever=slower unlocking=longer dwell time. I suspect, without knowing, that the switch to the beveled firing pin stop was to make it easier to rack the slide to charge from Condition 3 for limp-wristed GIs, and to help function of dirty guns.
Lighter mainsprings make it easier to get a light trigger on 1911-types. One can go down to a 17 lb. or lower mainspring and still get good ignition, but unless the loads are light to moderate and the slide is a full 5-incher, the dwell time may be too fast for the magazine spring to catch up, and at a minimum, last or next-to-last round jams will occur. Increasing recoil spring weight, an often-suggested remedy, only helps a little if at all, and is somewhat self-defeating, since it speeds up the return-to-battery stroke of the slide. Get the recoil spring too heavy, and the gun will be converted from controlled round feed to "push feed," and the extractor snapping over the case rims will soon break the extractor.
Now is the point where those of you who really understand 1911-type pistols may want to go elsewhere, as what I write will be old hat to you.
As you all know, the 1911 was designed around a load running a 230 gr. bullet at about 850 fps., with a 5" barrel and slide to match. Originally, it had a 23 lb. mainspring and a 16lb. recoil spring, and the result was that it was extremely forgiving. Once we started trying to fool Mother Nature and Father Browning, things got interesting. First, there were wimpy target loads. Lightening the recoil spring and mainspring were about all it took to keep reliability. Then, there were .38 Supers, running a 130 gr. bullet at 1200 fps. or so, and again, not much was needed. Then, along came hot .45 loads, shorter, lighter guns, starting with Commanders with 4 1/4" barrels and matching slides with lightening cuts, and later, IPSC, and then, the 3 1/2", 3 1/4" and 3" guns, and 10mms, .45 Supers, .45 WinMags, .460 Rowlands, and lions and tigers and bears, Oh My! "Old Reliable" suddenly started having reliability issues.
It's all about the basic physics of inertia, momentum, levers and springs, and their interaction with each other. Lest anyone be overly concerned, there will be no formulae here, nor any quiz at the end. While I took 12 hours of university physics, it was only because my major required it, and I despised almost every minute, mostly because most physics professors just ain't right somehow. So, we'll stay qualitative and basically Newtonian. Much of what I've learned about the subject has come from trial and error, with lots of the "error" part, and other important information came from Dane Burns and other 1911 gurus.
For function to be reliable in a 1911-type, dwell time is critical. Dwell time is the time period between the primer igniting the powder and the slide slamming closed on the next live round. If the dwell time is a little slow, it is usually not a big deal, unless it is accompanied by short-cycling. With long dwell times, really good speed shooters start to complain, because they feel like they are waiting on the gun to finish, but function of the gun rarely suffers. I clearly and fondly recall when I was that good. Sigh... It is when dwell times get too short that problems start happening, and shorter, lighter slides and lighter springs shorten dwell times.
Heavier slides have more inertia, so it takes more recoil force to get the slide moving rearward. They also have more momentum when moving forward, helping chamber the next round, once the recoil spring gets the slide moving. The hammer resting (briefly) on the firing pin stop delays unlocking, so the heavier the mainspring, the less force reaches the slide when unlocking starts. It is the mainspring, far more than the recoil spring, that affects dwell time, especially on the recoil stroke. Heavier mainspring=slower unlocking=longer dwell time.
As regards unlocking, another major factor involves levers. In 1911A1 and later guns, nearly all of them have a smooth, rounded bevel on the bottom of the firing pin stop, where it contacts the hammer during recoil. I believe (correct me if I'm wrong--been too long since I actually held an original 1911) that the original 1911 design had a square bottom on the firing pin stop. This seemingly small difference is significant, because the square bottom fp stop significantly shortens the length of the lever portion of the hammer, where the hammer pin is the fulcrum. Shorter lever=slower unlocking=longer dwell time. I suspect, without knowing, that the switch to the beveled firing pin stop was to make it easier to rack the slide to charge from Condition 3 for limp-wristed GIs, and to help function of dirty guns.
Lighter mainsprings make it easier to get a light trigger on 1911-types. One can go down to a 17 lb. or lower mainspring and still get good ignition, but unless the loads are light to moderate and the slide is a full 5-incher, the dwell time may be too fast for the magazine spring to catch up, and at a minimum, last or next-to-last round jams will occur. Increasing recoil spring weight, an often-suggested remedy, only helps a little if at all, and is somewhat self-defeating, since it speeds up the return-to-battery stroke of the slide. Get the recoil spring too heavy, and the gun will be converted from controlled round feed to "push feed," and the extractor snapping over the case rims will soon break the extractor.
