The DPM springs finally arrived from Greece. Substantially stiffer to rack. The DPM RAMI springpack is a
two-spring solution (like comes stock),
not triple springs as described on the webpage
https://dpmsystems.com/cz-2075-rami-b-db-30-barrel-9mm-40sw :
"MECHANICAL RECOIL REDUCTION SYSTEM
This system works due to the multi spring intricate rod (three springs) and controls the functionality of the gun. The third spring which is contained within the rod controls the movement of the slide so it never rams on the frame. Also three separate external springs accompany this system. The springs are different in length with the longest being heaviest when the slide is on the battery, so the shooter can fine-tune the weapon for his/her personal standards."
April 21, 2018 Update:
Digging in a bit with measurements, the stock RAMI outer spring is #18 AWG spring wire (1.024mm; 0.0403"), 11mm OD, 33mm Free Length, 6.5 coils with closed and ground ends. The DPM Systems Technologies outer springs are exactly the same diameters, but 51mm, 58mm, and 62mm free lengths, and appear to be music wire (better stuff, hey, they
ought to be for the price!).
I was going to calculate the rates of the three DPM Systems Technologies for comparison with the factory stock spring using something like
https://www.thespringstore.com/spring-calculator.html when it dawned on me to simply use my Rapala digital fish scale and measure them directly. Doing so, with the slide gripped in the 3X5" card padded jaws (high spot dusted, but unnecessary) of my
massive YORK 150* vise, I came up with the following data:
SPRING PRELOAD, lbs MAX LOAD, lbs AVG. LOAD, lbs % INCREASE RAMI 33 2.0 17.8 9.9 0
DPM 51 4.0 23.0 13.5 36.4
DPM 58 7.5 23.5 15.5 56.6
DPM 62 7.6 24.0 15.8 59.6
So it appears that the series-coupled little inner spring compensates for the bulk of the differences between the three outer spring options in the DPM kit.
Hopefully the higher racking energy will suffice to properly absorb the increased kick of my "short barrel" duty ammo
https://underwoodammo.com/product/handgun-ammo/9mm-luger-p-90-grain-xtreme-defender/ per the reality of physics that higher-power ammo needs to be paired with stiffer recoil springs
http://www.czforum.com/forum/index.php?topic=5424.msg22926#msg22926 in order to not abuse the hardware.
For now I'm carrying with the 51mm spring until I have opportunity to verify that the higher preload DPM options aren't
too beefy for the (short barrel limited) kick of the Underwood ammo, i.e., won't prevent full slide travel and thus rechambering.
I've advised DPM that I'm grateful that they have provided the springs I need to carry safely in absence of factory support (in terms of recoil spring inventories). For the record I'm also grateful for (industry-highest quality, imho) Underwood Ammo for offering product that enables my 2.93" barrel length invisible Subcompact carry pistol to punch above its weight!
Stay tuned...
*(http://www.york.cz/en/workshop-bench-vices-york-text) as scored in my youth (for $35.00; now retailing for $462.64!) while working at a Jawa-CZ motorcycle dealership...