I use them for elk (but also for deer and I'll even keep the same setup for pronghorn). This will sound crazy to some on here, but I use a 125 gr. Zwicky 2-blade BH glued to a 125 gr. steel adapter to bring the BH weight to 250 gr. This gives me a total bolt weight of 650 gr. with 2219s(good medicine for big elk ribs) and they fly fine. I haven't had any trouble with the flight and I don't really notice flight differences from changing spine. I have shot 100 gr. heads and 250 gr. heads with the same bolt/ crossbow and they both fly fine from my crossbow. Definitely not needed for WT deer (or the muleys I hunt here in Colorado), but for elk, I'm learning that I always want heavy and for me that means at least 600 gr. Another thing that I've noticed with heavy bolts. I did a test a while back to see how much different shooting a 400 gr. bolt and a 650 gr. bolt would be. I shot using one pin set at 20 yds. and shot at 15 and then at 30. With the 400 gr. bolt- the impactdifference between 15 yds and 30 yds was 9". With the 650 gr. bolt, the difference was 11". Adding 250 gr. only made a 2" difference at these yardages. I think maybe at longer distances (50 yds or so) it might make more difference, but for my hunting situations, the advantages of a heavy bolt far outweigh a slight disadvantage in range limitations. As far as your question, 170 gr. isn't too heavy as long as it flies good from your crossbow.