POA - POI, related to projectile weight and load velocity?

[Steve]

I used to know a little bit about this, very little, but that was a long long time ago. So I am appealing to the vast expert experience to be found here. I know I can look this up in JT's bog bore book and I am overdue to read it again but I was hoping to speed up my education by a few days.

So here is my scenario: I have a 45 Colt Ruger mid size flattop. My front sight is a .330 fiber optic blade and my rear sight is a Bowen rough country V blade, cranked all the way down. My POI at 25 yds is 2 inches high using 225 grain silver tips at just under 900 fps. I am planning to work up a load for everyday ranch work using a 265 grain Keith hard cast bullet and would like to be in the 900 plus range but not all the way to max loads. Please remind me how velocity, bullet weight and recoil affect POI vs POA. I am at the limit for lowering my rear sight unless I do some file work or have a taller custom fiber optic or gold bead front sight made. The tallest I could find from anyone readily available was the .330 I am using. Thank you for your time and help.

Steve

[JM]

If I recall correctly, the heavier projectile has slightly longer dwell time in the barrel during the recoil phase & will generally hit a bit higher than a lighter projectile.

Does that sound accurate?

[bradshaw]

Dec 6, 2017 8:23:07 GMT -5 Steve said:

I used to know a little bit about this, very little, but that was a long long time ago. So I am appealing to the vast expert experience to be found here. I know I can look this up in JT's bog bore book and I am overdue to read it again but I was hoping to speed up my education by a few days.

So here is my scenario: I have a 45 Colt Ruger mid size flattop. My front sight is a .330 fiber optic blade and my rear sight is a Bowen rough country V blade, cranked all the way down. My POI at 25 yds is 2 inches high using 225 grain silver tips at just under 900 fps. I am planning to work up a load for everyday ranch work using a 265 grain Keith hard cast bullet and would like to be in the 900 plus range but not all the way to max loads. Please remind me how velocity, bullet weight and recoil affect POI vs POA. I am at the limit for lowering my rear sight unless I do some file work or have a taller custom fiber optic or gold bead front sight made. The tallest I could find from anyone readily available was the .330 I am using. Thank you for your time and help.

Steve

*****

Read my answer to randyb’s thread under Double Actions, Question Regarding Sight Adjustment and Heavy Bullet. A Dick Thompson (a.k.a. sixshot) fix of building up front sight with epoxy may put you in business. Don’t file down rear sight, as the shallow notch makes for a weak sight picture.

Full cure is a taller front sight. Bag the heaviest bullet you plan to use, two or three 5-shot groups nice and tight. Measure to 1/10-inch----center of group (Point of Impact) above Point of Aim.

Rest
POI is the same whether shooting from a sandbag rest, Creedmoor, prone, the various sitting positions, kneeling, or offhand. If POI differs between rest and offhand, the shooter has work to do. Rube Goldberg contraptions, plastic or metal cradles, do not qualify; unless, of course, POI is the same as from a natural position and the gun never jumps or throws a shot. Note: there is no steadier natural position than CREEDMOOR. Creedmoor----in which the handgun does not touch the ground----relies entirely on gravity. Creedmoor affords the longest sight radius possible. Those who anatomically cannot assume Creedmoor, should try the dead frog, likewise gravity-based, with Creedmoor eye relief.

Formula
Sight Radius x Error divided by Distance to Target = Correction. All measurements in inches.

Example
To use my Ruger 03 Bisley Blackhawk 5-1/2” as an example: sight radius 7.2” x error 2” = 14.4”, divided by distance 900” (25 yds) = correction .016”.

A heavier bullet prints higher. Shoot and measure. Carefully bag the revolver with both loads. You may then calculate exactly how high the front sight must be to ZERO your heavy bullet @ 25 yards. You may be able to find a suitable fiberoptic blade.
David Bradshaw

[bigbrowndog]

Whose FO is it?? And is it dovetailed into the rampl?? Is it a standard dovetail if so?? If it’s pinned in then you could go with a dovetailed front FO and just have a 3/8” dovetail cut into your ramp and then have a FO sight height range of up to .50 and taller.

Because your 225gr load is so soft, you may be out of luck in getting a significantly heavier bullet at the same velocity to impact close enough to be useful, without a maojor change in sight system.

Trapr

[Steve]

Thank you for all the great answers. It is a pinned in sight. I suspect I will be looking at custom fabricated front sight blades, maybe with a gold bead. I am gonna bet I will end up needing a .350 like the factory black ramp blade.