7x57 in the CZ 550--various test loads


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Cosmoline
January 19, 2003, 11:47 PM
Took my new CZ 550 out for a test run through some 7x57 handloads. I've detailed the results below. In general, it appears the CZ 550 has been given a different twist rate than old military 7x57's. Where those rifles tend to do better with heavier bullets in the 175 grain range, the CZ 550 seems to be doing much better with bullets of 150 or 140 grain. I'm going to be working up a handload for the 139 Grain Horandy to about 2,800 fps--the one O'Conner used so much. That should be ideal. Here are some details:

195 Gr Barnes originals with 43 Grains IMR 4350, Winchester Brass and CCI standard large rifle primers.
Somewhat disappointing load. These bullets are AWESOME, with .345 SD and .570 BC. However, they came in 4 inches low and in a 2 1/2 inch group at 100 meters. Not too good. I may switch powders to try to pick up some speed and elevation. May switch to 4064 as that always seems to be giving me more power.

175 Gr. Barnes XFB with 42 grains of IMR 4064. Win. Brass and CCI standard large rifle primers.
The reverse problem. Too high. This one grouped better than the 44 grain hot loads I'd done before. 2" group at 100 meters coming in about 3" high. I suspect they may still be running too hot with that 4064 to be consistent with the other loads. I'm going to back the pressure off a bit more and switch over to 4350 for my next batch. Then these should drop down and, with the 195 gr. on the hotter 4064 they should rise up. Ideally they'll all meet in the middle and shake hands.

150 Gr. Winchester cheapos with 42 grains 4064. Win. Brass and CCI large rifle primers.
Great load, getting 1 1/2" groups at 100 meters. I suspect with better bullets it would be 1". A lot of these Winchesters came with their lead tips squashed. But they were real cheap at Midway, so who's complaining? Not me.

100 Grain Barnes solids with 40 grains of IMR 3031. Win Brass and CCI large rifle primers.
My squirrel load. These are real small bullets for the cartridge, but they shot just fine. Five shots inside a 2" group at 100 meters. Most small game shots will be well within fifty yards, so that's fine accuracy.

Next up--duplicating Jack O'Conner's famous 139 Western loads. I think this is the perfect rifle for them.

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xtarheel
May 3, 2003, 04:15 PM
Cosmoline: Any update? I'm about to embark on a similar quest.

Cosmoline
May 3, 2003, 05:03 PM
Wow! That's an old thread. As near as I could figure, CZ had decided (probably rightly) that most modern shooters would not be shooting heavy bullets out of a 7x57. I can't remember if I tested the twist rate on the 550 or not, but it did seem to be geared for smaller bullets, under 140 grains. That's what the rifle shot best, anyway. It did super well with very high velocity loads firing very small bullets. Due to these problems, I sold the rifle and have now turned my attention to very heavy 220 grain loads out of an old '91 Argie. I've got some detailed posts on that over on Paralax's reloading forum.

What I've learned from all this is--match the load to the rifle. Don't expect a modern rifle, no matter how well made, to like the same loads its forebears preferred.

xtarheel
May 3, 2003, 05:18 PM
Good points. That is why we have to continually reinvent the wheel as new powders and bullets are intorduced. My "new" 7X57 has a 23" 1 in 9 barrel with a tight chamber. The action is a very good 1942 Brno (DOT) Model 98 with lapped lugs and tight headspace. Using bullets in the 140 - 160 range, I'm wondering If I can safely work up to the neighborhood of .280 Remington loads. I know published loads are loaded down in deference to the many 100 year-old rifles in this chambering. It also seems to be common knowledge that Europeans commercially load this round to significantly higher pressures than their American counterparts.

Cosmoline
May 4, 2003, 12:42 AM
I've never feared putting my face behind any '98 action in good condition. To my knowledge, they are able to handle quite a bit more pressure than a 7x57 can generate. This assumes it's in good condition with good headspace, of course.

db4
May 6, 2003, 04:39 PM
I used to load for a Ruger M77 in 7x57; it had a fairly tight chamber but a long throat and a long magazine. Bullets could be seated quite long and still be short of the rifling and fit the magazine. 139-140 gr max tended to be lightly compressed IMR-4320 loads for nearly 3000 fps. 154 hornady's went 2900 with IMR4350, and my hunting load was the 160 Nosler Partition with a compressed load of IMR4350 for 2850 fps. All these shot about 1.5 MOA, as good as the Ruger would do with anything, and gave no scary pressure signs and good case life. Most .280's are hard pressed to do as well.

These loads are well above book maximums and were carefully worked up to in this rifle and chronographed; I would not use them in any other rifle without the same care. They do give an indication of the potential of this fine cartridge.

Have fun with your load development db4

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