MTMilitiaman, yes, differences can just be differences, but in many cases differences can also make one thing better than another. If differences never made any difference, we would not make any progress. Flintlocks are different than current rifles, but by no means are they on equal ground.
Do you really think the differences being discussed here resemble in magnitude the differences between a modern rifle and a flintlock? Differences can be improvements, and indeed, we find that all improvements generally occur as differences from contemporary. So all improvements are differences, but not all differences are improvements. Most of the time, as is the case here, we find that changes made to solve some problems create problems of their own. Despite their differences, the FAL, M14, and the G3 all demonstrated very good reliability, and exhibited excellent durability. The designs might not have identical reliability and durability, but they are close enough in that regard that the differences don't matter. They have no practical applicability to the individual rifleman in the field. Any advantage one design has over another is minute enough to be nearly impossible to quantify. If something can not be measured or proven, and has no literal effect in practice, it's theoretical.
The force that acts on the case in roller-delayed blowback occurs in the chamber, and on the case itself, not in the rifle action. It also only occurs after pressure has dropped to a safe level and the bullet has already fired from the barrel.
SO, by your logic, there is no forces acting on the bolt group, receiver, or locking surfaces of the rifle until the bullet has exited the muzzle? And this is accomplished in your little mind, how, I wonder? A secret application of German Pixie Dust? The Germans can just defy physics now? Cause making forces just disappear...that is a neat trick.
In truth, energy in a system does not just disappear. Conservation of Energy is a well accepted physical property.
Indeed, as these images from HKPro demonstrate, forces are clearly at work on the bolt and locking rollers. From: http://www.hkpro.com/technical.htm
F1 = Bolt Head Face Force
F2 = Receiver Force
F3 = Bolt Force
F4 = Bullet Force
F5 = Cartridge Shoulder Force
F6 = Resulting Maximum Force
It should follow, logically, that since this is a closed system, the forces that act on the case are then transferred to the bolt head, and from there, into the rest of the system.
Look, the G3 is a fine rifle. It is. It's durable, it's reliable, and it's more accurate than it needs to be. But all the rifles being discussed are durable, reliable, combat proven platforms. While I am not discounting that each design may have advantages in either over the other systems, I am strongly supporting the notion that these advantages are semantic until quantified, and that all are at least adequate in each of these areas. So any theoretical advantage the differences in your design give it compared to the M14, FAL, AK, M16, ect., is irrelevant until it can be applied appreciably and measurably in use. When dealing with designs so closely matched in practical performance, i.e reliability, accuracy, durability/service life, it becomes prudent to consider other smaller factors that may tip the advantage to one design or another. And when you consider things like sights, trigger, recoil impulse, control placement, ergonomics, and so on, the G3 doesn't compare to most of these designs in many of these factors. The AR and the M14 both have much better stock triggers than the average roller lock, as well as better sights. The AR, FAL, and M14 all have better control placement than the G3, and most find the G3's ergonomics inferior to all but the AK in the designs being discussed.
Now many, if not most of these things can be fixed, at least to a degree, with aftermarket support available for the roller locks. But the question still then becomes, why? What advantage does the G3/HK91/clones offer over an M14, a FAL, or an AR? Why buy a PTR-91 and then pay to have a trigger job done to it, a paddle style mag release, an ambi safety, and a port buffer installed on it, and still be stuck with a stamped receiver rifle that produces felt recoil many find excessive for a rifle of its caliber, an inconveniently placed cocking lever, and no bolt-hold open? By the time the modifications are done to it, hundreds of dollars are likely to be invested, which largely eliminates the initial advantage in cost the roller lock might have. I can spend a few hundred dollars more than the initial price of the PTR-91 and get an M1A (or a ________) that is going to be functionally at least as reliable, durable, and accurate, with better placed controls, a BHO, and is what is universally regarded as among the softest shooting rifles of its caliber.
Individual civilian riflemen don't normally bust down doors or clear rooms. Many, in fact, shoot relatively little at all, and when they do are content to sit their butts down on a bench and turn money into noise sending rounds at a controlled rate down what it in reality a tragically short 100 to 200 yard range. Then they pack it up, clean it up, and put it away. With the reputations any of these rifles have established under much more adverse conditions in the field, it is foolish to assume any of these rifles is going to have much of an advantage in reliability. All are going to run fine. Likewise, most riflemen, myself included, are unable to practice enough to maintain a level of competence capable of shooting most of these designs to their potential in terms of accuracy. This is especially true of those who fail to practice shooting field positions. The AK is the least accurate of these designs, but most are still capable of 3 to 4 MOA and easily capable of 200+ yards from field positions, even if most shooters are barely capable of blasting a 10 inch pattern on a target less than half that range. The AR and the Big Three can all probably hold 2 MOA or less with most ball rounds and much better with match ammo. That is enough to take the operator out to 500+ yards if he/she is able, as I've confirmed with my factory stock M1A Loaded. And of course, with proper maintenance, none of these rifle will normally see enough use by its original owner to not be passed down for several generations in good working order. I just don't see where the PTR-91 has many advantages. Mags are cheaper. But, ahhhh that's about i-no wait...yep. That's it. Mags are cheaper. I'll take $25 to $30 mags and second-to-none iron sights as an acceptable trade...