Most .223 varmint rounds whether ballistic tip or soft point are 55gr. Hornady makes a good consistant round. I still have some Coyotee 55gr. sp , These were loaded into LC surplus Brass. They did a great job.
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Do you want less pelt damage or are you simply trying to put them down as humanly as possible?
If you want less pelt damage there is two schools of thought.
1. Use FMJ through the lungs and they will not go far. Small hole in and out.
2. Use a light fragile bullet which will cause an internal wound cavity and not exit.
If you don't care about the pelt I would use what ever 50 to 55 gr SP that shoots accurately in the rifle of your choice.
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I guess I'm more worried about bullet stability in the 1:7 twist (my rifle). I've heard that 55gr is as low as I should shoot.
The 1:7 is a fast twist (one turn in every 7 inches vs the slower one turn in 9 inches). It should be able to stabilize a heavier bullet, but it's kind of academic, since a 55 grain soft point should be fine for coyote.