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Buy a brick, at least 500 rounds of fairly good 22 ammo. It doesn't need to be expensive target ammo, just something that the velocity will be pretty consistent on. On each range trip fire 5 rounds or so of the 22 ammo and record the average velocity. Use the same 22 rifle for this each time BTW.
Even with expensive chronographs the velocities they record will vary quite a bit because of differences in the sun's angle, and intensity. Temperature and other atmospheric conditions can effect velocity as well.
If you get readings with the 22's that are higher or lower than normal then you should expect to get the same with the centerfire ammo you are testing that day. Sometimes even at different times on the same day as temperature and the suns angle changes. If you are using the chronograph for more than an hour I'd recheck with the 22's occasionally.
If you get normal speeds with the 22's but your centerfire ammo is shooting faster than expected then you know the load may be a little too hot. If you are getting faster than normal speeds with both the 22's and your centerfire ammo it may just be that your chronograph is recording speeds a little fast in those conditions. This helps give you a better idea as to whether your loads need tweaking or not.
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