Absolutely yes, ammo can easily have that much effect on your accuracy. As a rule of thumb, core locts are great for hunting, terrible for shooting...they're a good bullet construction, they'll kill what they hit, and you don't really need any better than 3" at 100yrds to kill a deer, but for targets, they suck. They're certainly the most inaccurate popular selling non-surplus round available.

2.5" grouping isn't bad, and that size of change in POI isn't really that surprising...Without even changing brand or model series, simply changing bullet weight or bullet type you might notice much worse changes. Take my Ruger M77 for example, two Winchester Supreme 150grn bullets, one the Balistic Silvertip, the other the power point plus...the BST's shoot amazingly well, cloverleaf groups at 100yrds off a bipod, while the power point plus' are spread out to about 3" at 100yrds, and the POI is shifted down about 3" (same horizontal luckily), while Winchester Super-X soft points shoot about 5" groups and are 3" low and 6" left of the Supreme BST group...and that's just with Winchester ammo. Changing from Win Supreme BST 150grn to 165grn opens my groups up from a clover to about 1.5-2", and drops me about 2" (heavier bullet, makes sense at least).

I shot some FMJ surplus ammo (comes 8rnds to a CLIP for M-1 Garand for $2-I just want the CLIPS) out of that rifle one time, TERRIBLE groups, and that's only after I found out where they were hitting!!! I wasted two clips worth before I moved the target up to 25yrds and found out I was about 12" off of my normal POI AT 25yrds!!! Of course, out of my Garand, they give 12" groups at 600yrds!!

What load/bullet your gun likes can be extremely specific. Don't be surprised if you notice much worse changes in the future...but that certainly is a testimate to the quality of Core lokts, decent at best.