re: A rule of thumb on changing point of impact on fixed sighted guns

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To clarify more, the slower moving trajectories show higher impact before the 100 yard zero solely because the different velocities are shown at a 100 yard zero.

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Correct, this is because of compensation in bullet drop. (Aiming/angled higher)

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AlxTgr

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Why be a troll on the OB? The rest of the forum offers plenty of opportunities.

I won't discount the chart above, but the Mod 60 vid I posted clearly shows the gun moving upwards before the bullet exits. I think it fair to say there could be a combination of factors.

I may have messed up on my physics equations but it's been a little while since I have used them. All numbers are made to be easier in equations and not representative of actual numbers.

I am using a .223 size bullet with approximate speeds and a 16" barrel vs a 6" barrel.

16" rifle will be 4lbs and 6" handgun will be 2lbs.

@ 3000 ft/s @ 16" it takes approx. .00044 seconds at terminal and .00088 at average.
@2750 ft/s @ 16" it takes approx. .00048 seconds at terminal and .00096 at average.
@3000 ft/s @ 6" it takes approx. .00017 seconds at terminal and .00034 at average.
@2750 ft/s @ 6" it takes approx. .00018 seconds at terminal and .00036 at average.

difference between 3000ft/s and 2750ft/s at 16" is 8.7%

difference between 3000ft/s and 2750ft/s at 6" is 5.7%

recoil energy calculations were done with 55gr and 62 gr bullets with 30gr of powder.

55gr 3000ft/s 30gr with 4lb rifle = 7.87 ft/lbs
55gr 3000ft/s 30gr with 2lb handgun = 15.73ft/lbs
62gr 3000ft/s 30gr with 4lb rifle = 8.95 ft/lbs
62gr 3000ft/s 30gr with 2lb handgun = 17.9 ft/lbs

difference in 55gr and 62gr with 4lb = 12.84% (1.08 ft/lbs)
difference in 55gr and 62gr with 2lb = 12.9% (2.17 ft/lbs)

assuming all numbers are correct, recoil is negligible but more pronounced between bullet sizes on a smaller gun. However, the difference in time in the smaller barrel is also miniscule and doesn't change enough to warrant a significant difference in time in barrel for recoil to set in IMO. Please correct if needed.

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I may misunderstood the op. Might have meant bullet shoots higher (lands on paper higher) at same aiming point not you have to aim higher.

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Rule of thumb is for identical sight pictures at sub 100yd targets.

You did calculations for a .223.
How about a pistol round like a .45 LC.

I've heard that heavier rounds will impact high on targets several times.
I didn't believe it, but in my model 10 .38, it proved true.

I agree with the op.

You gave math to my reasoning.

You already proved it wrong once, do the math again and prove them wrong again!

All numbers are made to be easier in equations and not representative of actual numbers.

I am using a 45LC size bullet with approximate speeds and a 2" barrel vs a 3"" barrel from a Judge.

2" handgun will be 2lbs and 3" handgun will be 2.5lbs.

@1032 ft/s @ 2" it takes approx. .00016 seconds at terminal and .00032 at average.
@929 ft/s @ 2" it takes approx. .000179 seconds at terminal and .000358 at average.
@1032 ft/s @ 3" it takes approx. .00024 seconds at terminal and .00048 at average.
@929 ft/s @ 3" it takes approx. .000269 seconds at terminal and .000538 at average.

difference between 1032ft/s and 929ft/s at 2" is 11.2%

difference between 1032ft/s and 929ft/s at 3" is 11.39%

recoil energy calculations were done with 200gr and 250 gr bullets with 41gr of powder.

200gr 1032ft/s 41gr with 2lb 2" Judge = 26.84 ft/lbs
250gr 929ft/s 41gr with 2lb 2" Judge = 30.32 ft/lbs
200gr 1032ft/s 41gr with 2.5lb 3" Judge = 21.47 ft/lbs
250gr 929ft/s 41gr with 2.5lb 3" Judge = 24.25 ft/lbs

difference in 200gr and 250gr with 2lb 2" Judge = 12.17% (3.48 ft/lbs)
difference in 200gr and 250gr with 2.5lb 3" = 12.16% (2.78 ft/lbs)

assuming all numbers are correct, recoil is negligible but more pronounced between bullet sizes on a smaller gun. However, the difference in time in the smaller barrel is also miniscule and doesn't change enough to warrant a significant difference in time in barrel for recoil to set in IMO. Please correct if needed.

Slight interesting on the numbers for the much lighter gun though.