Need help with group analysis

[Roudy]

In fact I may need group therapy, but that's not what I mean this time! 

I was trying out a new 22 magnum Ultra Varmint rifle and things were going as expected until I shot a group at 100 yards that had about 1/2 inch vertical dispersion but 3 inches of horizontal dispersion. 

Was using CCI Maxi-Mag ammunition and there was some slight wind.  The same ammunition had previously grouped four shots in 1/2 inch at 50 yards so I was surprised to get such a wide horizontal dispersion.

This is a new rifle and new scope.  I've polished the bore with Flitz and intend to take another pass at it.  Rubber washer installed to free float the barrel, but intend to use a little JB Weld for a more solid bedding around the forarm screw.

Any comments on the cause of the horizontal dispersion would certainly be appreciated.

Roudy

[45/70fan]

Try changing the tighteness of the forend screw with and without the washer.

[Roudy]

Thanks for the feedback 45/70fan. 

I put the data into a ballistic calculator for the CCI round I was shooting and found that the bullet will drift 3.69 inches at 100 yards with only a 5 MPH wind blowing from 90 degrees.  I was really surprised that the 33 grain bullet with a 2300 fps muzzle velocity would drift that much, but it seems my target bears that out!

Roudy