Cant tighten groups

[BarryL]

This rifle will shoot groups in the 5's and 6's and now I cant get it under about 15 or so. I went from Lapua brass to winchester for 6.5-284 and ladder tested a load. They are centered and fairly round. Im at 51,2gr. H4831sc, fed 210m primers and 142gr. with a .020" jam MK's. ES is good. What should a guy try now? Rifle has 800 rounds down the barrel.

 

[mikecr]

Swap out your scope just to rule it out. You never know..

 

[6Dasher]

Have any of the old brass left. Try those against the winchesters.

 

[Woodman]

Have you had it out of the stock? The wrong action screw torque spread your group.

 

[BarryL]

No old brass left and it hasnt been out of the stock. I can loosen off the screws and check the torque before the next session. Im thinking maybe back off the jam in .005" incrememts and see if that does anything.

 

[AlanPF]

Barry,

I used to jam the SMK 142s, mainly because that't what everyone does, then tried jumping them .020 and at the longs, elevation is much better.

However to me your problem sounds more like some sort of fouling or change in the barrel. I'm wondering if the first few inches past the throat may need some attention with JB paste or similar - this is often recommended to be done every 200 rounds. Dave Tooley recommends it, so nothing more needs to be said!

Alan