CZ Scorpion and the quest for the perfect load.

[Geeman]

I bought a CZ Scorpion and I've been working with some 9mm loads to find what I'm going to fill an ammo can. 

I'm running a LabRadar (Doppler Radar) to read speeds and I'm really liking this thing.  I ran 13 strings of different loadings with a total of 75 shots, and if failed to read just one of those shots.  The unit sits a foot to the side if the muzzle and all that is necessary is lining it up to the target and your good to go.  Absolutely nothing in front of the firing line.  A big thumbs up from me!!!

Now something odd I found with the Scorpion.  Its a stationary barrel (7.75") blow-back design.  It ate absolutely everything with out a hick-up.  The odd thing is the velocity of the first shot of the string was the lowest of the string on 11 of the 13 strings I fired today.  I suppose the force of the massive breech block differs when manually closed than that of returning after a shot.  Something I wasn't expecting, and certainly something I need to pay attention to when developing loads.  An example is my two AA7 (8.2g) strings ...

Stats - Average   1371.44   fps
Stats - Highest   1394.8   fps
Stats - Lowest   1303.94   fps
Stats - Spread   90.85   fps
Stats - Std. Dev   38.16   fps

The string
Shot V0
1    1304
2    1379
3    1388
4    1391
5    1395

And the identical load repeated...

Stats - Average    1371.44   fps
Stats - Highest   1393.29   fps
Stats - Lowest    1310.87   fps
Stats - Spread    82.42   fps
Stats - Std. Dev    34.09   fps

The string...
Shot V0
1   1311
2   1385
3   1385
4   1383
5   1393

It seems to be something that is happening with almost all strings, but AA7 seems to be worse than most.  The extreme spread is horrible, but take away the first shot and its EXTREMELY uniform.

Learn something new every day...

Greg

[The_Shadow]

That is a little odd, could it be the barrel is cooling off more than it is between shots?