Listed below are some (not all) modified blowback actions
categorized with my nomenclature – makes sense to GONRA anyhow…
“gas buffered blowback” – late WW II German Volkstrum 7.92x33 rifles,
9mm HK P7 pistol, South African Vector pistol (recalled?).
Believe some poor soul tried this in a 12 ga. shotgun design too. Yikes!!!
“delayed blowback” – Remington 51 pistol and their new R-51 pistols
are only common examples in US.
Blowback starts up, stops, restarts and finishes the selfloading cycle.
“retarded blowback” – examples include a variety of foreign SMG’s,
some Italian rifles and light MG’s, H&K roller-cam rifles and pistols
(remember 1960’S era literature that leads one
to believe H&K tried this on a .50 BMG rifle and gave up),
original Thompson SMG (its NOT the “Blish effect” its RETARDED BLOWBACK fellas!)
SIG-AMT modified roller-cam, FAMAS lever amplification, various Benelli broken toggle
(all require fluted chambers) and the .276 Pederson broken toggle
(smooth chamber so VERY THIN GREASE required on cartridge cases!)
“cartridge case-chamber friction retarded blowback” –
examples include MAB Model R 9mm pistols that have spring loaded barrels
(small coil spring), various 5.7x28FN FiveseveN firearms and the Ruger-57 pistol –
with spring loaded barrels. (FiveseveN pistol spring loads barrel with a torsion spring).
5.7x28FN firearms designer had the freedom to spec / optimize a brand new cartridge.
Common cartridges cannot necessarily withstand the axial stretching force
without the cartridge case head blowing off. 5.7x28 FN obviously handles well.
Believe Ruger just copied it but never got one to eyeball….
When 5.7x28FN caliber pistol goes BANG, coefficient of STATIC friction is important first,
then once cartridge starts slipping out of the chamber,
switch to coefficient of DYNAMIC friction.
(Brave souls out there can try shooting longer cartridge case CCI Stingers
in some of the small .22 RF long rifle pocket pistols.
Have gloves and safety glasses on when the cartridge case head blows off!
Even braver souls could try to make some lathe turned 5.7x28FN cartridge cases
from high strength steel that won’t expand to “grab the chamber”,
shoot handloads and “see what happens”.
>>> NO - DO NOT DO THIS ! <<<
Wouldn’t be a HUGE deal with conventional short recoil pistols,
but could easily blowup the FiveseveN, probably Ruger-51 too!!!)
Bottom line - any math model of these FiveseveN type actions
sure needs exceptionally detailed knowledge of the friction coefficients!
Usually isn’t the BIGGEST deal in firearms math models,
but here its just as important as “inertial” and “spring loaded” terms
in the dynamic equations!
Weird – but have to admit my FiveseveN “shoots Just Fine”!
Have fun in any event, and DON’T blow yer head off!