30-30 model 94 question

[atr]

shooting a 30-30 model 94 short barrel (carbine)
with J's 170 gr FN pretty much dead on for windage (about 2000 fps)
But
with cast 180 gr RN they are shooting 3" LEFT of center (again about 2000 fps)

I don't understand the 3" windage difference.
any thoughts?
thanks
atr

[Zingger]

Crazy thought- hear me out. What is the powder you are using? Fast vs slow and the amount of complete burn before it leaves the barrel. The pressure seems to screw with the harmonics of the barrel (whip). I have a trapper 94 and have experienced what you have. Also the meplat of the bullet will cause some differences in poi/poa. I scrapped the old trusty Lyman altogether when I bought the RD 165 mold. And I run it plenty warm, but it will perform next to a jacketed. Hope this helps.

[Der Gebirgsjager]

This isn't meant to be a simpleton answer, although it may seem like one. It is not uncommon for jacketed bullets and cast bullets to shoot to different points of impact. Could be the higher velocity of the jacketed load exiting the barrel faster. But, you seemingly have two options: Chose the load you want to shoot the most and adjust the sights for that load, then compensate for the load used less often. 3" is just the width of the bullseye on many targets, so hold center for the jacketed and at the right edge of the bull for the cast. Or, the second alternative is to get into load development, using different powders and charges until the desired result is obtained. Different weights of bullets should also be in the mix.

[kungfustyle]

I think Zingger is onto something. I have a 30-06 that shoots a Hornady bulk 150 spitzer bullet about two inches left, while the Sierra Pro hunters will hit dead center. Something to do with harmonics and BC. The wind will also funk with the flight, ie if the wind is blowing left to right, it will have one effect verses right to left. I've seen a chart that looks like an S showing impact zone of different length bullets vs wind direction. I guess the spin/bc of the bullet will "drift" one way or another.

[MT Gianni]

The bearing surface of the bullets are different, and it isn't an unusual occurrence.

[dverna]

I do not understand how bearing surface affects POI. My bet would be barrel harmonics.

Mounting a receiver peep sight or tang sight would allow you to adjust for each load. Trying to find an accurate load with two different bullets that will shoot to same POI might prove challenging.

[Bird]

Heavier bullet= more torque effect on barrel. R/H twist in barrel causes opposing torque to the left. A possibility maybe?

[atr]

Hi guys,
the powder I am burning is Win748 and gives very accurate loads with both cast and J's.
I use the same load(s) in a Savage 340 (30-30) and the POI does not show that same amount of windage variation.
The idea of barrel harmonics IS an interesting thought.
thanks guys.

[Bazoo]

Did you ever make any further determination on this?

[Wag]

Barrel harmonics.

--Wag--