Odd windage difference between 38 and 357 in lever rifle?

[kyron4]

Sighted in my 16" Rossi 92 with factory iron sights. At 25 yds the 158gr 38 FMJ's hit dead center about 1.5" high, all holes touching. Switched to 158 gr 357 mag FMJ's and the group 1/2" below center as expected but was about 1.5" to the right, again all holes touching. Drifted rear sight and got group centered, switched back to 38's and now they were 1.5" to the left. I repeated this several times with the same results. What would cause this ? Is this normal ? I'm at a lose. I ending up splitting the difference and now 38 is 3/4" left of center and 357 is 3/4" right of center. Very confused. Any thoughts ? -Thanks

 

[denton]

Not surprising.

The culprit is probably barrel whip.

When the rifle fires, the muzzle begins to vibrate. If bullets exit at different points in the cycle they will land at different points on the target. The 38 and the 357 probably have very different barrel transit times.

 

[cdb1]

It is normal. Denton nailed it.

 

[Tommygunn]

I have a Browning B-92 in .44 magnum. It is one of the most accurate long arms I own ..... in .44 mag, not so much in .44 special.
My solution?
I shoot .44 magnums in it.
At 25 yards (in OP's case) barrel whip is the culprit.

 

[loose noose]

I have the Henry Big Boy in .357/38 and at 50 yards the .38 will print directly POA POI and the .357 will print about 1.5"-2" below POA but still in line with the .38's BTW the Henry is quite a bit heavier than the Rossi, and therefore probably less barrel whip. I did have a Rossi about 10-15 years ago that was a really nifty little carbine, but was in .45 Colt, I do remember that being exceptionally light, but very accurate. Wish I still had it.