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Thread: Bullet drop lighter-heavier bullets

  1. #1

    Bullet drop lighter-heavier bullets

    Question for you, folks.

    I have my .22 wmr zeroed at about 75 yds, and was using 40 gr. ammo at the time, as well as ever since. The other day I was in my RFD asking for wmr ammo, and he handed me a box of 30 gr. Curious to try something different, I shot a group of 5 earlier today and was surprised to see it grouping about 1" low, the opposite of what I would have expected (i.e. that lighter ammo would drop less and therefore group high, if anything). The group was also slightly to the right, but there was a slight crosswind blowing that way.

    Now, admittedly it was only 5 shots, so maybe not enough to go on, and I was shooting without any sticks/bipod or anything, from a sitting position, with legs splayed and elbows resting on my thighs, so my aim probably wasn't optimal, but all 5 holes were in the same 1" group to the lower right. Is there any general rule about shifting elevation when switching to lighter grained bullets, and vice versa?

  2. #2
    When I alternate between 60gn and 100gn in my .243 the height of the group doesn't alter but it moves a couple of inches left. Like you, I would've expected the heavier ammo to drop further, but clearly there's more science behind it than sheer weight! Barrel harmonics, probably. It's all a bit mysterious...

  3. #3
    If one changes the make or bullet weight of a cartridge on should re-zero the rifle. Say at your 75 yards and then see how much the bullets drop at say 100yds. This drop difference can then be compared to the same procedure with your old 40gr ammo.
    So many variables, say your 30gr bullet has less recoil, less muzzle rise before the bullet exits and shoots therefore lower than the 40gr with more recoil, more muzzle rise.
    edi

  4. #4
    Thanks very much for the replies.

    My knowledge of ballistics is very low still, with simplistic assumptions the result! And as you both point out, there are a fair few variables involved...

  5. #5
    Quote Originally Posted by VSS View Post
    When I alternate between 60gn and 100gn in my .243 the height of the group doesn't alter but it moves a couple of inches left. Like you, I would've expected the heavier ammo to drop further, but clearly there's more science behind it than sheer weight! Barrel harmonics, probably. It's all a bit mysterious...
    VSS, out of curiosity would the 2 types of ammo be identical, other than weight?

  6. #6
    So, you have made the classic mistake of thinking the bullet is dropping! the lighter bullet has not reached the peek of its trajectory and so is lower.
    Hypothetically; Lets say you have a rifle and held it so it cannot move and fire a 50 grain bullet, it will go through the sight line at about 25 yards reach its peek at about 90 and then start dropping.
    Change that bullet for a 40gn and it will still go through the sightline at about 25 yards, reach its peek at 100 and then start to drop.
    Therefore the 40gn will be lower at 75yards.
    My 243 has the following trajectory, 47 yards bang on with all bullets, peek at various ranges, 100gn= 150yards, 85gn=185yards, dead on at 200 with 85gn and 100gn then drops of rapidly 2" low at 250yards with 85gn and 5" low at the same distance with 100gn.
    I used to enjoy loading and finding out what the trajectories were.

  7. #7
    You can play around with this for theory and try it out on the range.I've found it to be a good guide.

    The best advice comes from experience like levigsp

    Ballistics Calculator - Hornady Manufacturing, Inc

  8. #8
    nothing to do with "drop"

    trajectory is only comparable with a fixed zero
    your zero for each bullet weight and charge is dependent on the position of the muzzle in its harmonic cycle as the bullet exits

    think load testing with a fixed bullet weight
    charge weight can move the bullet around the target (I find it is usually an anticlockwise shift with increasing charge)

    My 60gr 40gr and 53gr .222 loads have all been tuned to hit within 1/2" at 100 yds but their comparable trajectory over say 300-400yds is different

  9. #9
    Quote Originally Posted by levigsp View Post
    So, you have made the classic mistake of thinking the bullet is dropping! the lighter bullet has not reached the peek of its trajectory and so is lower.
    Hypothetically; Lets say you have a rifle and held it so it cannot move and fire a 50 grain bullet, it will go through the sight line at about 25 yards reach its peek at about 90 and then start dropping.
    Change that bullet for a 40gn and it will still go through the sightline at about 25 yards, reach its peek at 100 and then start to drop.
    Therefore the 40gn will be lower at 75yards.
    My 243 has the following trajectory, 47 yards bang on with all bullets, peek at various ranges, 100gn= 150yards, 85gn=185yards, dead on at 200 with 85gn and 100gn then drops of rapidly 2" low at 250yards with 85gn and 5" low at the same distance with 100gn.
    I used to enjoy loading and finding out what the trajectories were.
    This response really helps clarify what's going on for me. Many thanks.

    When you say that the bullet reaches the sightline at about 25 yds, I presume that with the discrepancy between barrel height and scope height it takes that long for the bullet to reach that line, then it carries on gaining height until peak trajectory?

  10. #10
    Quote Originally Posted by levigsp View Post
    So, you have made the classic mistake of thinking the bullet is dropping! the lighter bullet has not reached the peek of its trajectory and so is lower.
    Hypothetically; Lets say you have a rifle and held it so it cannot move and fire a 50 grain bullet, it will go through the sight line at about 25 yards reach its peek at about 90 and then start dropping.
    Change that bullet for a 40gn and it will still go through the sightline at about 25 yards, reach its peek at 100 and then start to drop.
    Therefore the 40gn will be lower at 75yards.
    My 243 has the following trajectory, 47 yards bang on with all bullets, peek at various ranges, 100gn= 150yards, 85gn=185yards, dead on at 200 with 85gn and 100gn then drops of rapidly 2" low at 250yards with 85gn and 5" low at the same distance with 100gn.
    I used to enjoy loading and finding out what the trajectories were.
    Sorry in this case you have it all wrong. Firstly the bullet starts dropping the moment it leaves the barrel. Every bullet does. The moment the lighter bullet leaves the barrel (at higher speed) it should at any distance and at any time be higher. Logic. (if we presume the same BC)
    edi

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