Cosmoline
Member
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.
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.