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When duplicating 9MM +P loads for a CZ 75 with a 4.7 inch barrel, how does one determine a safe load? I am working with Alliant Power pistol and 115 and 124 gr XTPs. I estimate the .7 inches of extra length are good for about 50 fps over the book loads for 4 inches.
 

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loader

Good selection, that CZ-75. I owned and shot one in IPSC competition about 15years ago and found it very forgiving of my loading follies. Like many shooter/reloaders of that vintage I was trying to make Major power levels. I did too, but every once in awhile it would blow out the case wall just in front of the rim and cause the magazine to get blown out the bottom by the escaping gases! Needless to say, not knowing when this was going to happen kind of ruined my concentration! My scores were NOT helped by shooting Major! Incidently, I credit the steel reinforced Pachmayer grips with saving me from injury. I am pretty certain the stock plastic grips would have shattered.

There was once an excellent article in Shooting Times on loading Major, years and years ago. The keys were:

Use good brass, (once and once only!);
Use enough slower powder to make the required velocity; and
Use good jacketed bullets.

You have what seems to be one of the best powders and some of the best bullets already selected so all you have to do is use new brass and load until you reach the required velocity. If Hornady loads 9mm +P loads, you can't go wrong by seeing what velocity they achieve and load up cautiously until a chronograph tells you that you have reached the required level. Don't bother re-using the brass. It will probably work for another load or maybe 5 but eventually one of those cases is going to let go!

Guessing pressure by primer appearance, case diameter, ease of extraction or number of loads before the primer goes in too easy are of little use at the pressures handguns are intended to operate at. Velocity is your best indication of pressure.

Good luck and stay safe!
 

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Kanuk -

Thanks for the fast response and good advice. If I do my math right, we are tryimg to make Major, which is bullet grains X velocity = 175000. Is that still correct?

If so, the same math requires 1412 fps with the 124 gr bullet, and that is way faster than i want to go. I am thinking 1270 to 1300 for the 124s.

Is that still one shot out of new brass for safety? Published Alliant data gives 1235 fps with Power pistol for a 125 FMJ and 6.6 grs of Power pistol in a 4 inch bbl (34,000 psi). I need 7.0 to go 1300 in the CZs 4.7 inch bbl. I should be up around 36,000 psi if I take no credit for the extra 0.7 inch bbl length.

Does this make sense?
 

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As I understand it, once we get outside the "normal" pressures/velocities for a given cartridge, the relationship between pressure and velocity isn't quite linear. That is to say that pressure can go up quite quickly while velocity doesn't seem to change all that much.

If 7.0gr of Power pistol gives you the velocity you hope to achieve, terrific. If I were you I would load up to 1,250fps with the 124gr Hornady and be happy. The extra 50 fps isn't worth the trouble. Absolute reliability and good accuracy are more important (in either competition or real life) than extra power.

As for brass and whether or not you should re-use it, I leave that to you. I was loading Major using a 160gr cast bullet sized down to .356" at 1,100 fps. It was tough on the brass but it did the CZ-75 no harm that I could see. The loads you are talking about would seem to be on the heavy side but no where near what I was running. If you are just shooting targets, reload the brass but inspect it carefully for cracks and dimples inside the case or discolouration outside the case just above the rim that suggests it is being over worked. After awhile you will get a feel for what the useful life of the brass is (3-5 reloads ideally).

If you are talking about loading ammo for serious work, in defence yourself and your family, load once into new brass and use that, or , better yet, use factory ammo.

Incidently, I'd still recommend the Pachmayer grips as the single most useful accessory for a CZ-75. The grip goes from square to nicely rounded and provides a much more secure grip, plus the added safety from a blown case.

Let me know how it works out.
 

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Kanuk -

Thanks again. I'm an old rifle loader, and even have a little ballistics lab out in the barn, but these semi-auto pistols are pretty new to me.

The powders are FAST and the cases are SMALL...kind of makes me pucker sometimes. So 1250 fps for the 124 XTPs and Pachmayer grips - I can do that.

Its funny how things work out. For my carry gun I poured a pile of money into a very nice SIG 229 with both the 357 SIG and 40 S&W barrels. This is a very nice set up with manageable recoil and good power.

When the CZ 75 BDs went on sale last spring I picked one up and never put it down. My scores went way up, as did my confidence. Next, I got the Kadet 22 upper, and ran a couple of cases of 22LR through it. Scores with the 9mm went up again.

Liked reloading the 9X19 so much, I got a Hi-Point 9 Carbine to use for load testing for $150 new. This ugly little piece of plastic took all the abuse I could throw at it and digested anything and everything. It graduated to House Gun when my non-shooting wife shot 10X with it at 25M. The 1250 fps CZ loads do 1500 fps out of the carbine so we are now a one load family.

Take care...
 
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