When I destroyed two CZ52 pistols in 2000 with experimental handloaded
overloads, and then could not harm Tokarevs with much higher overloads,
I found the weak spot, the bottom of the CZ52 chamber was very thin,
[.058" CZ52, .125" Tokarev], because the underside had been milled out
to make room for the roller blocks. I began to question the premise that
the CZ52 is stronger commonly printed in books, magazines, ammo
manufacturers etc., though out the gun culture.
http://www.thehighroad.org/attachment.php?s=&postid=249178
This is what I now believe probably happened to get this error into the
gun culture:
1) In 1970 the US army published an account of the CZ52 pistol.
Knowing that:
a) The Russians had a TT-33 pistol designed in 1933 that Russian Tokarev
ammo loaded to 31 k c.u.p.
b) The Checks had a CZ52 was designed in 1952 and that Czech 7.62x25mm
Tokarev ammo was 42 k c.u.p.
c) The CZ52 has a roller block locking system.
Fromthe U. S. Army Foreign Science and Technology Center's publication
titled"Small Arms Identification and Operation Guide - Eurasian
Communist Countries", (FSTC-CW-07-03-70), page 211, Table XI, Cartridge
Data and Color Codes, in reference to 7.62 x 25 mm pistol ball type P;
"Do not use Czechoslovak-made ammunition in TT-33 pistols."
2) In March 2000, I got a Letter [as did many others, and the letter was
handed out at the shot show] from Ted Curtis ballistician at Accurate
Arms. Ted Curtis, a very old ballistician already was bald and had jowls
in his 1966 photo in "Speer 7". All the typos are Ted's:
"7.62 X 25 Tokarev ..
Due to the large number of handguns imported into the U.S. chambered
for the 7-62 x 25 Tokarev Accurate Arms has developed the following load
data for those shooters who wish to reload the little powerhouse. In
determining the appropriate pressure limit for our load data we tested
various military ammo from China, Russia, Austria Bulgaria and the
Czech Republic. Commercial ammo produced by Sellier & Bellot was also
tested. Based on these tests we arrived at a maximum pressure for our
lad data of 42,000 C.U.P. Only the single lot of Russian ammo was
significantly below this pressure averaging 31,000 C.U.P. The consistent
pressures between all other type sand manufactures was a welcome
surprise . Indeed, the fact that CZech ammo, made for the CZ-52 pistol,
produced the same pressure as that of the other countries was perhaps
the biggest surprise of the whole project. This in spite of the "tribal
lore" regarding this particular handgun and the ammo loaded for it
claiming that shooting Czech ammo in any other firearm so chambered will
causes spontaneous disassembly. The pressure data produced by the ammo
tested certainly doesn't support this theory.
[Ted presented some loads with AA#2, AA#5, and AA#9 that were at 42 k
c.u.p. and very high velocity]
...We feel that the maximum loads shown here are suitable for the CZ-52 so
long as the firearm is in good condition. Other models of foreign
handguns of a lessor quality should probably be loaded in a more
cautious manner. "
3) What I believe happened was that:
a) 1970 the army was not aware or did not realize the implication if
China, Poland, and Bulgaria were also producing 42 k c.u.p. Tokarev ammo
and it was for their domestically produced Tokarevs. The army's
technical writer working on the paper either did not have a CZ52 sample
in 1970 or was unwilling to do destructive tests, unwilling or unable to
do a mechanical strength analysis, or was distracted by the roller
locking mechanism.
b) If Czech ammo for CZ52s is 42 k.c.u.p. and is the same as 42 k
c.u.p. ammo China, Austria, Bulgaria, and Poland make for their
Tokarevs, the ammo being used does not imply the CZ52 is stronger.
c) When Ted measured the communist block Tokarev ammo, he realized
there was an error in the 'tribal lore', but he did not realize that his
data implied that the rational [ used infer the CZ52 was stronger than
the Tokarev] was gone. He then published his loads for "the CZ52 only".
2000
1) I blew up 2 CZ52 pistols that split the barrels
2) Ken Marsh pointed out that the crack propagation seemed to start from a thin spot in the chamber chamber where there was undercutting for space for the roller blocks.
3)I notified AA in 2000 that I was blowing CZ52 up with small percentage
overloads of their 2000 data.
4) When I notified Sierra [a very good company with a very good rifle
handload book] that their "CZ52 is stronger" line in their handgun load
book was wrong, I got a typical reaction, ~ "We are impressed with your
load data, but we were just printing what WE read."
5) When I notified GUNWORLD magazine that their line, "The CZ52 is
stronger" was in error, Jan Libourel wrote me that he was just ~"
printing what HE read".
6) When I posted on the internet that "The CZ52 is not stronger" I
got many negative reactions from CZ52 owners that missed the nuance
between [that CZ52 are not as strong as the Tokarev] and [that CZ52s
will blow up with factory ammo].
2003
1) Jaque Clarke "Uncle Jaque", a CZ52 owner, makes a drawing of this thin spot.
2) I am unable to blow up any of my Tokarev pistols, with what blows up CZ52s and much more.
3) I bought a broom handle 1896 Mauser 30 Mauser to compare to CZ52 strength. It blows primers, but does not blow up at the loads that blow up CZ52s. I cannot go higher with these primers.
In 2004 AA took the CZ52 load data off their web site.
2005:
1) John Becrovitz and I buy 10 CZ52 barrels and tests them for hardness. Measurements between RC25 and RC35 were taken on intact 7.62x25mm barrels. A more modern 9mm CZ52 barrel tests at RC47. What does it all mean?
My 9mm CZ52 barrel steel might yield at 220ksi, while my 7.62x25mm Tokarev CZ52 barrel steel might yield at 120 ksi
2) Accurate Arms "revised" their hot loads for the CZ52 only. This example is for 110 gr SPR RN 1.3":
a) The hot load from 2000: 11.7 gr AA#9 41,800 c.u.p 1688 fps
b) The wimpy load from 2005 8.5 gr AA#9, 34270 psi, 1248 fps
