Bullet drop lighter-heavier bullets

Sako75Hunter

Well-Known Member
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?
 
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...
 
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
 
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...
 
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?
 
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.
 
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
 
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?
 
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
 
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?


that above is a hypothetical scenario
in practice any of the bullets in your rifle could land above or below any other bullet at 25 75 or 100yds

its the same reason your POI shifts with a mod with the same load
 
Yes that's it.
However that 25 yards is Hypothetical.
Each calibre and rifle is different due to bullet speed, height of scope etc. with a .22 I normally think about 15-20 yards, .243 45yards, etc.
I normally aim to get rabbit, fox and roe rifles no more than 2" above the line of sight, bigger deer rifles 3" etc. hope that helps.
 
VSS, out of curiosity would the 2 types of ammo be identical, other than weight?

No.
The 60grn are home loaded Sierra HP over 45.2grns of N150.
The 100grn are factory rounds (T Mantel), just because I wanted a few heavier ones in my cupboard just in case I ever get the opportunity to shoot anything bigger than a fox :rolleyes:. I couldn't justify the time and trouble working up a handload for such occasional use.

To alternate between the two I just need to adjust the windage turret the appropriate number of clicks. No need to re-zero each time.
 
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And let's not forget that heavier bullets tend to be longer bullets with a better ballistic coefficient - in effect have less drag to their momentum and thus maintain there velocity and hence a flatter trajectory over longer ranges, even if they start a bit slower than lighter bullets.
 
And let's not forget that heavier bullets tend to be longer bullets with a better ballistic coefficient - in effect have less drag to their momentum and thus maintain there velocity and hence a flatter trajectory over longer ranges, even if they start a bit slower than lighter bullets.

Interesting point there Heym, thanks
 
In most cases it's a very simple bit of physics. The heavier bullet has a longer barrel time (slower velocity) and therefor the angle of departure of the bore as the rifle recoils will be higher. The faster bullet has a lower angle of departure as it is in the barrel less time during the (often lighter) recoil cycle. Anyone who has spent time regulating a bullet to a set of iron sights will be very familiar with this.~Muir
 
In most cases it's a very simple bit of physics. The heavier bullet has a longer barrel time (slower velocity) and therefor the angle of departure of the bore as the rifle recoils will be higher. The faster bullet has a lower angle of departure as it is in the barrel less time during the (often lighter) recoil cycle. Anyone who has spent time regulating a bullet to a set of iron sights will be very familiar with this.~Muir

Right, so the heavier bullet produces more recoil, resulting in a steeper trajectory, but reaches peak trajectory sooner than the lighter bullet due to its lower velocity?
 
Right, so the heavier bullet produces more recoil, resulting in a steeper trajectory, but reaches peak trajectory sooner than the lighter bullet due to its lower velocity?

No
Velocity and time in barrel is important but ONLY as a factor of barrel harmonics (the flexible whip as the rifle goes off)

your barrel is doing this:


308mode1.gif

http://www.varmintal.com/308mode1.gif

the POI at a fixed distance is related only related to where on the cycle it exits the muzzle.
you can adjust your zero to whatever you like
fire a lighter bullet and you will get a different poi based on the muzzle position in a harmonic cycle (not recoil or aim related)

some heavier bullets will land high, some low
my 208gr load lands lower than my 180gr load in my 300wm for example


peak trajectory is not relevant unless you are comparing Bullets zeroed at the same range.
zero your war at 300 and the peak will be higher.
zero a slower bullet and a faster one at 100 and the slower one will probably need a higher peak to hit zero at the same distance.

you are asking why two bullets of different weight hit a target at different points when ONE of them is zeroed at 100yd
 
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