Help with encore 204

[long range engineer]

I have a encore with a thompson center 204 barrel. I was trying to sight it in today and at 25 yards and the bullets were tumbeling. The holes in the paper were very keyholed. I am shooting factory hornady 40 grain loads. I have not done anything to the rifle other than mount my scope. Any help would be greatly appreciated.

 

[MachV]

Give the barrel a good cleaning with a carbon remover is the standard answer but it don't sound like you got enough rounds down the barrel for that to be a problem......Still worth a try! Another thing to check is the crown?
You may also wan to give the 32 grainers a try?
I like the 204 but its a fussy devil sometimes!!

 

[Gunpoor]

LRE, the Encore barrels chambered in 204 have a 1/12" rate of twist and sometimes they won't stabilize the 40 grain bullets. Bullets making keyholes in the target means the barrel is not sufficiently stabilizing the bullets. I have the Encore Prohunter barrel in 204 and it will shoot the 40 grain Hornady V-max very well from my handloads, though I don't know if it the extra 2" of barrel length or what that makes this possible. As posted by MachV, maybe you should try a bullet with less mass/length and see if that will remedy this.