In the Hi-Point thread
www.sksboards.com/smf/index.php?topic=55436.0 I made reference to the Hi-Point using a straight blowback method of operation. Many shooters may not understand the differences between straight blowback and locked-breech pistol operation (as typified by the 1911, SIG, Glock etc.) Coincidentally in the June 2009 issue of
Handloader magazine, there is an article on the subject by Charles E. Petty. Seeing as he can explain it better than me, I will mainly use his technical description of both methods of operation.
STRAIGHT or SIMPLE BLOWBACKThe simplest autoloader works on the principle of straight or simple blowback where, after firing, the case pushes back against the slide, and the energy overcomes the inertia due to the mass of the slide causing the slide to retract. The extractor brings the fired case along for the ride until a point where it hits the ejector and is thrown out of the way. At the same time the magazine spring is using some of its stored energy to push a fresh round up in time so the slide - now closing under mainspring tension - can strip it from the magazine into the chamber. Of course this all happens in mere fractions of a second.
The bottom line issue in the function of all automatic pistols is
the management of the forces generated by a cartridge when it fires. In a blowback system, the WEIGHT of the slide and/or PRESSURE of the mainspring must be great enough to keep the breech closed until the bullet exits. It is not mechanically locked in place except for the weight of the slide and pressure of the mainspring. With higher intensity cartridges the weight needed can become a problem. The beauty of this system is its stark simplicity and low cost. The barrel is fixed in place at all times and thus eliminates an accuracy variable as well.
The straight or simple blowback system is the standard type in .22 rimfire pistols where it has excelled. The normally accepted maximum for straight blowback actions is the .380 ACP. The Russians wanted a straight blowback type pistol similar to the Walther PP .380 for their post-WWII service pistol and in experiment they decided that the 9x18mm Makarov was as far as they could push the design and still retain a reasonable slide weight and spring force. To be sure there have been some blowback 9mms or even a .45 ACP, but those have had massive slides or springs that defy mere mortal men. Here I'm thinking [
Charles Petty talking] of the old Astra 400 that was one of the most unpleasant 9s I've ever shot. You better eat your Wheaties, too, if you try to compress that spring. Another example is the AMT Backup in 9mm that also used the power of the mainspring against the hammer to help hold things down. There have been some other blowback 9mms and even a .45 or two that probably were better boat anchors.
Although we all know and love Bond's PPk, the fact is, it isn't a great joy to shoot, and the locked-breech .380s, such as the new Ruger LCPs, give the shooter a light, compact pistol with very manageable recoil and quicker shot-to-shot recovery times. Economy-priced blowback .380s are larger and heavier than locked-breech .380s which could be considered a negative if concealed carry is the purchase purpose.
This system has also worked exceptionally well in non-pistol sub-machine gun applications like the STEN, Uzi, and even guns we can buy like the Hi-Point 995, and most others of this type where a heavy bolt is totally acceptable. It allowed the manufacture of subguns for an incredibly low cost per unit and with a rapidity that was sorely needed in wartime.
LOCKED-BREECHVirtually all of today's automatics of 9mm or larger caliber [Hi-Point excepted] use John M. Browning's tilting barrel, locked-breech mechanism. The importance of this arrangement is that it INCREASES THE RECOILING MASS to include both the slide and barrel, so everything is slowed down a little to give the bullet time to get out of the barrel and allow the pressure to drop before the slide continues backward by itself and ejects the fired case.
There are variations in this theme among many designs, and the barrel doesn't have to tilt to fit the general "locked-breech" category. One of the best known examples would be the locking mechanism used on the Beretta Model 92 or U.S. M9 service pistol. The mechanism doesn't really matter nearly as much as the principle that keeps the slide and barrel locked together. Once the bullet has left the barrel, the lockup releases, and there is more than enough momentum to carry the slide back for the rest of the cycle.
By far the most common locked-breech design used today is some variation of Browning's tilting barrel. Most pistols slides today are simply drilled at the front to provide the same function as the bushing, and barrels can be easily removed from the rear. Unlocking is done by cam surfaces on the barrel that mate with areas in the frame or, now with the modular construction of polymer frame pistols, the barrel seat section. Very often the forward edge of the ejector port also serves as an upper barrel locking surface.
The essential element is that there is some mechanical means of keeping the barrel up and locked and then pulling it down to unlock. The most obvious is the 1911 barrel lug/barrel link arrangement where the slide stop pin rides along the flat of the barrel lug for around 0.15 inch before the barrel link can pull it down and unlock. Many of today's polymer guns compliment flat surfaces on the barrel seat in the frame and barrel with an angled cut that pulls the barrel down an the right time. The barrel only has to drop 0.009 to 0.010 inch to unlock.
The beauty of the locked-breech system is that you end up with a much lighter slide and/or mainspring which in turn makes the whole pistol lighter and reduces felt recoil as well, even with larger, higher pressure rounds like 9mm Luger, .40 S&W and .45 Auto. While the tilting (or other type) of barrel system introduces a non-fixed barrel into the accuracy and reliability picture, as well as increasing machining costs, in actuality these are non-issues as modern locked-breech guns are the mainstay of target shooting and have overcome all the ills that plagued them through their first century, and today it is so rare as to be newsworthy to get a new gun that
doesn't work well right out of the box. This type of autopistol rides in almost every cop's holster and is standard issue to virtually all Western armed forces.
And lastly, we all certainly owe a debt of gratitude to an unassuming self-taught kid that grew up in frontier Ogden Utah that went on to develop the system that most autoloaders use a century later - John Moses Browning.
