Grouping advice

[BluGrass]

So I took my new to me 110FP out for the second time today trying out different factory ammo. Haven't started reloading yet. This is 10 shots at 100 yards with Winchester Match 168gr. which it really seems to like. My question is why did my group string horizontally like that? Opinions and advice would be appreciated.
http://tapatalk.imageshack.com/v2/14/09/01/8a8b9ae00d897a87c2b9a94c2bcae90a.jpg

[Texas Solo]

Barrel heat? POI shift after some fouling rounds?

[justdave]

Action screws/ scope mount still tight?

[BluGrass]

Checked all my screws last night before I took it out. I'm thinking its barrel heat like Texas Solo said. I didn't really let it cool down during. And it was about 90 degrees in the shade. Gotta love this Southeast Texas weather.

[foxx]

my '06 A-Bolt will walk right off the paper at 100 yrds if I shoot 5 consecutive shots like that. Cold bore, it's easily .5 inch shooter.

[Digduggy]

My 111 in 30'06 walked up and left with heat...

Also, clean would be the exact opposite...

Something I have to see with my new cbi barrel... Not seeing the heat walk so much with it... Im sure barrel nut and recoil lug may have something to do with that as well