different loads causing a windage change?

[milktree]

I just loaded up some of .357 Mag. for my Marlin lever gun.

I shot it at 50 yards with the new ammo and the mouse fart .38 special I usually run through it.

Both loads use the same projectiles (Montana Gold 125 gr FPRN).

The new .357 mag ammo goes 2,200 fps with a SD of 14.4; it's pretty consistent

The .38 Spl runs about 996 fps with a SD of 33.2, but groups well.

I'd expect the elevation of the two to be quite different, based on the more than 100% difference in speed, the .357 hit about 3-1/2" higher.

What's weird is that the .357 hit about 2MOA to the left.

Is it normal for a different load to hit that much different in windage?

 

[TrashcanDan]

Is it normal for a different load to hit that much different in windage?

Short answer is yes. Because I've done it in my henry and 627.
Velocity is more of the determining factor.
All loads using 160 gr, 38 spl for the whellgun landed next to 38 spl from the henry (moves a little faster out of the rifle) landed close to the .357 for the wheelgun which was close to 3" left to the .357 for the rifle.
.38 was bullseye powder. .357 was 4227.

All groups were consistent, just not near each other.
With the powder charge being the same for both .38's and both .357's, I chalked it up to a velocity difference between a 4" barrel and a 20" barrel.

Real noticeable difference with 180 gr .357 and a max charge for that gr wt head. Groups were consistent, but the landing point grew.

I've also had it happen with S&B 9mm, going from 115 gr to 124 gr. Not a huge difference in weight. Not a huge difference in velocity. Groups landed about 3" apart.

Longer answer might be velocity vs. r.p.m.'s.

 

[gerrycaruso]

This is both loads out of the same gun right? I'm guessing the barrel vibration is different between those two loads.

 

[meh]

I've seen this, too, but I haven't thought about it all that much. Just pausing for a moment to do that, it seems to me that there are two complicating factors. One is that most lever guns don't have free floating barrels, so you've got this point of contact at some point down the barrel that is probably going to prevent an "orderly" oscillation of the barrel. But it's still going to do something. Second, even with a free floating barrel, I suppose the oscillation isn't necessarily vertical. You get elevation shift downrange with different velocities, of course, but the barrel oscillation might add to or subtract from what would be there on account of bullet drop or muzzle rise before the bullet leaves the barrel. Likewise, why couldn't it be oriented at an angle to the receiver...especially with the complication of the magazine tube in the mix?

 

[milktree]

This is both loads out of the same gun right? I'm guessing the barrel vibration is different between those two loads.

Yes, same gun.

Something else that occurred to me is that I probably wasn’t totally consistent with my technique holding the rifle on the bench.

And even if I was, the different recoil would move my support hand/arm differently.

Clearly I should try again with better technique.

 

[mac1911]

Yes, same gun.

Something else that occurred to me is that I probably wasn’t totally consistent with my technique holding the rifle on the bench.

And even if I was, the different recoil would move my support hand/arm differently.

Clearly I should try again with better technique.

Any changes induce a change somewhere.
Barrel harmonics, your hold, your anticipation of more recoil.

If your looking to test the loads get a rifle rest like a lead sled. Take as much as you out of it.
I have had point of impact shifts with the “same” factory load but different lot if ammo.

Really want to have fun. Get a decent pellet gun and half dozen types of pellets. See how much it varies with just pellet changes.