Cooper rifles

Have you chronographed the loads yet?
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I chronographed the 79gr loads at 3300fps. In my other 7mmstw rifles, 79gr produces from 3400fps to 3450fps. This rifle has a lot of freebore, which I am attributing some of that to. I loaded to 3.7" to fit the magazine, and all bullets that I tested were at least .1" from the lands. As well, it was only 5 degrees C out this morning, which could also be a bit of a factor. Based on my other rifles, each grain adds about 50fps, so I am estimating the 82gr load at somewhere around 3450fps. Given that the Barnes data lists 3360fps out of a 24" barrel for 82 gr, and I have a 26" barrel, that matches up quite close. I will find out for sure next weekend if the weather is cooperative.
 
I chrongraphed again today, with better light conditions, and the 82gr load was producing 3595fps, or way too hot. I backed off to 80gr, and the 80gr loads chronographed 3434fps at +4 degrees C. I fired four groups at 200 yards to sight in the rifle, and the average of the four groups was a bit under .900". Sub 1/2moa at 200 yards is good enough for me with a hunting rifle shooting the TTSX. It should be noted that IMR 7828 is somewhat temperature sensitive, so that velocity will increase noticeably in warmer weather. I expect to see in the 3460 fps to 3470fps range at 20degrees C.
 
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