Let’s discuss some of the factors affecting the functioning of pistols in general, and short 45’s in particular. To contribute to this discussion, head over to SigForum and join in.
Let’s imagine a theoretical pistol, say a .45 caliber firing a given load, in which magazine timing efficiency and lockup were basically constant values. This means that the magazine requires a minimum period in which to present rounds before the breechface, and that the barrel and slide remained mechanically locked together for a set travel.
Let’s say that the variables at play are barrel length and spring tunnel length in proportion; slide mass; breechface over-run (it’s rearward travel past the magazine that, in part, dictates how much time the magazine is given to do it’s job); and recoil spring rate / weight.
Shortening the barrel length reduces total reciprocating mass, while increasing bore pressure at the muzzle which drives slide velocity as a function of the jet effect of expanding gas behind the bullet.
Thus, if we make our theoretical .45 shorter, we get faster unlocking and higher slide velocity due to reduced mass, AND even more slide velocity driven by higher residual bore pressure. Besides rendering our theoretical pistol unpleasant to shoot, excessive slide velocity has obvious consequences in the form of increased wear and breakages, plus the possibility of recoil-induced magazine malfunctions like double feeds and the like. We’ve agreed that in this pistol we can’t decrease slide velocity by increasing lockup travel to (partially) compensate for reduced slide mass.
Yet, our shorter pistol has room for an even shorter recoil spring that is taxed to do even more work in less travel and with fewer coils in a shorter space. So, an obvious answer is to use a heavier-rated spring to slow that slide down. It makes sense.
There are some problems and limitations at work against us here, however. First, our shorter spring needs to exert even more pressure in battery to attenuate the increased speed of unlocking from our lighter slide; to accomplish this, we can open up the coil spacing but at the expense of significantly reduced service life as we see with the various small 1911-style guns. One workaround: the multui-strand spring that SIG has pioneered already. However, that spring’s large net wire diameter limits how short it can go. Another? The flat-wound spring type.
So, let’s say we can engineer a trick 26-pound spring that gives us all the closing pressure against that light slide in battery we want, and slows down that gnarly slide velocity like a champ. Great!
The problem is that we’re up against another variable and one of our constants: we’ve had to shorten slide stroke considerably to arrive at this small package, and thus have reduced breechface over-run. Along with our ultra-strong recoil spring, we now aren’t giving the magazine enough time to function reliably.
Our choice of .45 ACP, being heavier and with a less-optimal transfer factor compared to other rounds like, say, 9X19, makes this timing even more critical.
So, we decide to lose the garage-door spring and back off the tension / rate just enough to allow the mags to feed, without permitting excessive wear and breakages from too much slide speed. Great! Our theoretical test gun survives a torture test in fine form on our test range, fed by a stack of new mags loaded by assistants.
Why, then, do our imaginary customers complain that their pistols start in with FTF’s after a few hundred rounds or so? That likely has to do with the difference in fatigue rates between magazine and recoil springs. The same physics are at play when we shorten the magazines, and magazine springs, as well. Unlike our torture-testers, our customers have only a few mags to work with, and as these mags take a set they no longer can keep up.
Yet another factor needs to be considered: extractor tension. Our imaginary light slide, short barreled pistol unlocks quickly with higher residual bore pressure, and thus requires more positive extractor tension as a hedge to overcome increased case adhesion forces during extraction.
Yet, that light slide carries with it much less momentum during the feeding cycle, and we can’t get as much closing pressure from that short spring to overcome the resistance that our increased extractor tension exerts upon the case rim as it tries to slide up the breechface, much less from a marginally-timed, short magazine with a less-than-adequate mag spring. Thus, the classic 3-point FTF jam we see all the time in short .45’s.
So, we can try another workaround to deal with feeding issues caused by both higher extractor tension and a reduced magazine timing window: we increase magazine spring tension to compensate. That, however, also has consequences as the slide has to overcome more resistance as it strips rounds out of the feedlips.
That, in brief, is an explanation of some of the fundamental problems that make shortened pistols so problematic. The tension between these factors is difficult to balance. If some of these factors seem familiar to your experience with various short .45’s, I hope it will help explain why I generally try to steer folks away from them.
I hope to lend some technical perspective to the subject of short pistols, and hopefully help explain my preference for at least somewhat longer guns. In a world of highly critical, perhaps over-engineered handgun designs, I believe a few extra coils of recoil spring, a bit more slide mass or a little bit longer slide travel can make all the difference.
I look forward to reading your informed input and alternative viewpoints. Head over to SigForum for the discussion.