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Discussion Starter · #1 ·
My job in the sandbox this time is as a fobbit. It is extremely boring and shared with people of little imagination. Forums like these are my only source of intellectual stimulation. So forgive me if my question sounds like one cooked up by someone with a lot of time on his hands. I've seen a lot of "FAL vs. CETME/G3" discussions on other forums. Ergonomics seems to be the most common comparison, but occasionally someone mentions reliability. Many point to the FAL's adjustable gas system as a plus for reliability and touch on the G3's lack of it as just fortunately not detracting much from reliability due to its recoil being overpowered. But the more I study it, the more I think of the roller delay as being self-adjusting. It appears to me that a low pressure cartridge will cause a longer delay in opening. But that is a good thing, since the bullet will take a little longer to exit the barrel and lower the pressure inside. Conversely, a high pressure cartridge will have less delay but still be safe due to the bullet exiting the barrel that much faster and again relieving excess pressure. Obviously, the fixed mass of the bolt and carrier are not variable so there would be a definite minimum and maximum end of the reliability/safety scale. But the lack of a need to tap gas from the barrel to unlock and open the bolt on the roller-delayed blowback would seem to make it less sensitive to the pressure-curve of the ammunition. Pressure would relate to bullet speed and bolt opening speed more closely in the G3 than it would in the FAL since port pressure in a gas system varies depending on the particular pressure curve of the powders used. Am I right, or do I just have too much time on my hands?
 

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I'm sure that there is an envelope of performance that will work just as you said.

To make a similar comparison, sometimes I load 110 grain bullets over the same charge that I use with the 155s I like to load when I have a hoser stage in 3 gun in effort to reduce recoil. The rifle cycles just fine even with the lighter bullets. Perhaps this "experiment" changes a different variable, but it stands to reason that the bolt thrust should be less when shooting a lighter bullet?
 

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There are also different locking pieces that are sometimes necessary to change out to make the roller-locked system function 100%. Such as an ammo change is made to a heavier/lighter weight bullet, or in a shorter barrel variant of the same weapon, or a suppressor is added to the weapon. This is the "variable" part of the HK roller-locked system.
 

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There are a variety of locking pieces with different mass and shoulder angles. The angles help determine unlock times and pressures. There is a variance in all ammuntion manufacturer specs, and while a locking piece may be designed for one set of variables, it will work within a certain percentage above and below spec.
 

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Discussion Starter · #5 ·
I really appreciate the replies; you're helping to cement my understanding of this system. I read the HKPRO technical page on the system, but my math skills weren't up to the task of completely comprehending it. I can see why different locking pieces would be needed to adapt the rifle to bullet weights outside the design envelope. Just how big is that envelope? And is powder selection in terms of pressure curve much of a factor? Some rifles, like the Garand, are very sensitive to pressure curves and can be damaged by powders that burn too slowly. It leads to too high a port pressure that can bend op-rods. FAL's, even though they were designed for a "standardized" NATO round, include an adjustable gas system---not to accomodate slower powders but presumably because the NATO "standard" varies too much from maker to maker. Would it be accurate to say that the roller-delayed blowback of the G3 is tolerant of a wider range of bullet weights and velocities than the FAL can adjust for, and in that way it is more reliable? Or is it just more reliable than the FAL with varying ammo types, because the FAL might have to be adjusted when making an ammo change?
 
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